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The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, is a network of
controlled-access highway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms i ...
s that forms part of the National Highway System in the United States. The system extends throughout the
contiguous United States The contiguous United States (officially the conterminous United States) consists of the 48 adjoining U.S. states and the Federal District of the United States of America. The term excludes the only two non-contiguous states, Alaska and Hawaii ...
and has routes in
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
,
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...
, and
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and unincorporated ...
. The U.S. federal government first funded roadways through the Federal Aid Road Act of 1916, and began an effort to construct a national road grid with the passage of the Federal Aid Highway Act of 1921. In 1926, the
United States Numbered Highway System The United States Numbered Highway System (often called U.S. Routes or U.S. Highways) is an integrated network of roads and highways numbered within a nationwide grid in the contiguous United States. As the designation and numbering of these h ...
was established, creating the first national road numbering system for cross-country travel. The roads were still state-funded and maintained, however, and there was little in the way of national standards for road design. U.S. Highways could be anything from a two-lane country road to a major multi-lane freeway. After Dwight D. Eisenhower became president in 1953, his administration developed a proposal for an interstate highway system, eventually resulting in the passage of the Federal Aid Highway Act of 1956. Unlike the earlier U.S. Highway System, the Interstates were designed to be an all-freeway system, with nationally unified standards for construction and signage. While some older freeways were adopted into the system, most of the routes were completely new construction, greatly expanding the freeway network in the U.S. Especially in densely populated urban areas, these new freeways were often controversial as their building necessitated the destruction of many older, well-established neighborhoods; as a result of the many
freeway revolts Highway revolts (also freeway revolts, expressway revolts, or road protests) are organized protests against the planning or construction of highways, freeways, expressways, and other civil engineering projects that favor vehicles. Many freew ...
during the 1960s and 1970s, several planned Interstates were abandoned or re-routed to avoid urban cores. Construction of the original Interstate Highway System was proclaimed complete in 1992, despite deviations from the original 1956 plan and several stretches that did not fully conform with federal standards. The cost of construction of the Interstate Highway System was approximately $114 billion (equivalent to $ in ). The system has continued to expand and grow as additional federal funding has provided for new routes to be added, and the system will grow into the future. Though much of their construction was funded by the federal government, Interstate Highways are owned by the state in which they were built. All Interstates must meet specific standards, such as having
controlled access A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms ...
, physical barriers or
median strip The median strip, central reservation, roadway median, or traffic median is the reserved area that separates opposing lanes of traffic on divided roadways such as divided highways, dual carriageways, freeways, and motorways. The term also a ...
s between lanes of oncoming traffic,
breakdown lane A shoulder, hard shoulder (British) or breakdown lane, is an emergency stopping lane by the verge of a road or motorway, on the right side in countries which drive on the right, and on the left side in countries which drive on the left. Many wi ...
s, avoiding
at-grade intersections An intersection or an at-grade junction is a junction where two or more roads converge, diverge, meet or cross at the same height, as opposed to an interchange, which uses bridges or tunnels to separate different roads. Major intersections ...
, no
traffic light Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control flows of traffic. Traffic light ...
s and complying with federal
traffic sign Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest signs were simple wooden or stone milestones. Later, signs with directional arms were introduce ...
specifications. Interstate Highways use a numbering scheme in which primary Interstates are assigned one- or two-digit numbers, and shorter routes which branch off of longer ones are assigned three-digit numbers where the last two digits match the parent route. The Interstate Highway System is partially financed through the
Highway Trust Fund The Highway Trust Fund is a transportation fund in the United States which receives money from a federal fuel tax of 18.4 cents per gallon on gasoline and 24.4 cents per gallon of diesel fuel and related excise taxes. It currently has two account ...
, which itself is funded by a federal
fuel tax A fuel tax (also known as a petrol, gasoline or gas tax, or as a fuel duty) is an excise tax imposed on the sale of fuel. In most countries the fuel tax is imposed on fuels which are intended for transportation. Fuels used to power agricultural v ...
. Though federal legislation initially banned the collection of tolls, some Interstate routes are
toll road A toll road, also known as a turnpike or tollway, is a public or private road (almost always a controlled-access highway in the present day) for which a fee (or '' toll'') is assessed for passage. It is a form of road pricing typically implement ...
s, either because they were grandfathered into the system or because subsequent legislation has allowed for tolling of Interstates in some cases. , about one-quarter of all vehicle miles driven in the country used the Interstate Highway System, which had a total length of .


History


Planning

The United States government's efforts to construct a national network of highways began on an ''ad hoc'' basis with the passage of the Federal Aid Road Act of 1916, which provided $75 million over a five-year period for
matching funds Matching funds are funds that are set to be paid in proportion to funds available from other sources. Matching fund payments usually arise in situations of charity or public good. The terms cost sharing, in-kind, and matching can be used interc ...
to the states for the construction and improvement of highways. The nation's revenue needs associated with
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
prevented any significant implementation of this policy, which expired in 1921. In December 1918, E. J. Mehren, a civil engineer and the editor of ''
Engineering News-Record ''Engineering News-Record'' (widely known as ''ENR'') is an American weekly magazine that provides news, analysis, data and opinion for the construction industry worldwide. It is widely regarded as one of the construction industry's most authorita ...
'', presented his "A Suggested National Highway Policy and Plan" during a gathering of the State Highway Officials and Highway Industries Association at the Congress Hotel in Chicago. In the plan, Mehren proposed a system, consisting of five east–west routes and 10 north–south routes. The system would include two percent of all roads and would pass through every state at a cost of , providing commercial as well as military transport benefits. In 1919, the U.S. Army sent an expedition across the U.S. to determine the difficulties that military vehicles would have on a cross-country trip. Leaving from the Ellipse near the
White House The White House is the official residence and workplace of the president of the United States. It is located at 1600 Pennsylvania Avenue NW in Washington, D.C., and has been the residence of every U.S. president since John Adams in ...
on July 7, the Motor Transport Corps convoy needed 62 days to drive on the
Lincoln Highway The Lincoln Highway is the first transcontinental highway in the United States and one of the first highways designed expressly for automobiles. Conceived in 1912 by Indiana entrepreneur Carl G. Fisher, and formally dedicated October 31, 191 ...
to the Presidio army base on San Francisco Bay. The convoy suffered many setbacks and problems on the route, such as poor-quality bridges, broken crankshafts, and engines clogged with desert sand.
Dwight Eisenhower Dwight David "Ike" Eisenhower (born David Dwight Eisenhower; ; October 14, 1890 – March 28, 1969) was an American military officer and statesman who served as the 34th president of the United States from 1953 to 1961. During World War I ...
, then a 28-year-old brevet lieutenant colonel, accompanied the trip "through darkest America with truck and tank," as he later described it. Some roads in the West were a "succession of dust, ruts, pits, and holes." As the landmark 1916 law expired, new legislation was passed—the Federal Aid Highway Act of 1921 (Phipps Act). This new road construction initiative once again provided for federal matching funds for road construction and improvement, $75 million allocated annually. Moreover, this new legislation for the first time sought to target these funds to the construction of a national road grid of interconnected "primary highways", setting up cooperation among the various state highway planning boards. The
Bureau of Public Roads The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program a ...
asked the
Army An army (from Old French ''armee'', itself derived from the Latin verb ''armāre'', meaning "to arm", and related to the Latin noun ''arma'', meaning "arms" or "weapons"), ground force or land force is a fighting force that fights primarily on ...
to provide a list of roads that it considered necessary for national defense. In 1922, General John J. Pershing, former head of the
American Expeditionary Force The American Expeditionary Forces (A. E. F.) was a formation of the United States Army on the Western Front of World War I. The A. E. F. was established on July 5, 1917, in France under the command of General John J. Pershing. It fought along ...
in Europe during the war, complied by submitting a detailed network of of interconnected primary highways—the so-called Pershing Map. A boom in road construction followed throughout the decade of the 1920s, with such projects as the New York parkway system constructed as part of a new national highway system. As automobile traffic increased, planners saw a need for such an interconnected national system to supplement the existing, largely non-freeway,
United States Numbered Highways The United States Numbered Highway System (often called U.S. Routes or U.S. Highways) is an integrated network of roads and highways numbered within a nationwide grid in the contiguous United States. As the designation and numbering of these ...
system. By the late 1930s, planning had expanded to a system of new superhighways. In 1938, President Franklin D. Roosevelt gave Thomas MacDonald, chief at the Bureau of Public Roads, a hand-drawn map of the United States marked with eight superhighway corridors for study. In 1939, Bureau of Public Roads Division of Information chief Herbert S. Fairbank wrote a report called ''Toll Roads and Free Roads'', "the first formal description of what became the Interstate Highway System" and, in 1944, the similarly themed ''Interregional Highways''.


Federal Aid Highway Act of 1956

The Interstate Highway System gained a champion in President Dwight D. Eisenhower, who was influenced by his experiences as a young Army officer crossing the country in the 1919 Motor Transport Corps convoy that drove in part on the
Lincoln Highway The Lincoln Highway is the first transcontinental highway in the United States and one of the first highways designed expressly for automobiles. Conceived in 1912 by Indiana entrepreneur Carl G. Fisher, and formally dedicated October 31, 191 ...
, the first road across America. He recalled that, "The old convoy had started me thinking about good two-lane highways... the wisdom of broader ribbons across our land." Eisenhower also gained an appreciation of the Reichsautobahn system, the first "national" implementation of modern Germany's
Autobahn The (; German plural ) is the federal controlled-access highway system in Germany. The official German term is (abbreviated ''BAB''), which translates as 'federal motorway'. The literal meaning of the word is 'Federal Auto(mobile) Track' ...
network, as a necessary component of a national defense system while he was serving as Supreme Commander of Allied Forces in Europe during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
. In 1954, Eisenhower appointed General Lucius D. Clay to head a committee charged with proposing an interstate highway system plan. Summing up motivations for the construction of such a system, Clay stated, Clay's committee proposed a 10-year, $100 billion program, which would build of
divided highways A dual carriageway ( BE) or divided highway ( AE) is a class of highway with carriageways for traffic travelling in opposite directions separated by a central reservation (BrE) or median (AmE). Roads with two or more carriageways which are ...
linking all American cities with a population of greater than 50,000. Eisenhower initially preferred a system consisting of
toll road A toll road, also known as a turnpike or tollway, is a public or private road (almost always a controlled-access highway in the present day) for which a fee (or '' toll'') is assessed for passage. It is a form of road pricing typically implement ...
s, but Clay convinced Eisenhower that toll roads were not feasible outside of the highly populated coastal regions. In February 1955, Eisenhower forwarded Clay's proposal to Congress. The bill quickly won approval in the Senate, but House Democrats objected to the use of public bonds as the means to finance construction. Eisenhower and the House Democrats agreed to instead finance the system through the
Highway Trust Fund The Highway Trust Fund is a transportation fund in the United States which receives money from a federal fuel tax of 18.4 cents per gallon on gasoline and 24.4 cents per gallon of diesel fuel and related excise taxes. It currently has two account ...
, which itself would be funded by a
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...
tax. In June 1956, Eisenhower signed the
Federal Aid Highway Act of 1956 The Federal-Aid Highway Act of 1956, also known as the National Interstate and Defense Highways Act, was enacted on June 29, 1956, when President Dwight D. Eisenhower signed the bill into law. With an original authorization of $25 billion for ...
into law. Under the act, the federal government would pay for 90 percent of the cost of construction of Interstate Highways. Each Interstate Highway was required to be a
freeway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms ...
with at least four lanes and no at-grade crossings. The publication in 1955 of the ''General Location of National System of Interstate Highways'', informally known as the ''Yellow Book'', mapped out what became the Interstate Highway System. Assisting in the planning was
Charles Erwin Wilson Charles Erwin Wilson (July 18, 1890 – September 26, 1961) was an American engineer and businessman who served as United States Secretary of Defense from 1953 to 1957 under President Dwight D. Eisenhower. Known as "Engine Charlie", he was pre ...
, who was still head of
General Motors The General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. It is the largest automaker in the United States and ...
when President Eisenhower selected him as Secretary of Defense in January 1953.


Construction

Some sections of highways that became part of the Interstate Highway System actually began construction earlier. Three states have claimed the title of first Interstate Highway. Missouri claims that the first three contracts under the new program were signed in Missouri on August 2, 1956. The first contract signed was for upgrading a section of
US Route 66 U.S. Route 66 or U.S. Highway 66 (US 66 or Route 66) was one of the original highways in the United States Numbered Highway System. It was established on November 11, 1926, with road signs erected the following year. The h ...
to what is now designated
Interstate 44 Interstate 44 (I-44) is a major Interstate Highway in the central United States. Although it is nominally an east–west road as it is even-numbered, it follows a more southwest–northeast alignment. Its western terminus is in Wichita Fal ...
. On August 13, 1956, work began on
US 40 U.S. Route 40 or U.S. Highway 40 (US 40), also known as the Main Street of America, is a major east–west United States Highway traveling across the United States from the Mountain States to the Mid-Atlantic States. As with most routes ...
(now I-70) in St. Charles County. Kansas claims that it was the first to start paving after the act was signed. Preliminary construction had taken place before the act was signed, and paving started September 26, 1956. The state marked its portion of
I-70 Interstate 70 (I-70) is a major east–west Interstate Highway in the United States that runs from I-15 near Cove Fort, Utah, to a park and ride lot just east of I-695 in Baltimore, Maryland, and is the fifth-longest Interstate in the c ...
as the first project in the United States completed under the provisions of the new Federal-Aid Highway Act of 1956. The
Pennsylvania Turnpike The Pennsylvania Turnpike (Penna Turnpike or PA Turnpike) is a toll highway operated by the Pennsylvania Turnpike Commission (PTC) in the U.S. state of Pennsylvania. A controlled-access highway, it runs for across the state. The turnpike's we ...
could also be considered one of the first Interstate Highways, and is nicknamed "Grandfather of the Interstate System". On October 1, 1940, of the highway now designated I‑70 and I‑76 opened between
Irwin Irwin may refer to: Places ;United States * Irwin, California * Irwin, Idaho * Irwin, Illinois * Irwin, Iowa * Irwin, Nebraska * Irwin, Ohio * Irwin, Pennsylvania * Irwin, South Carolina * Irwin County, Georgia * Irwin Township, Venango County ...
and
Carlisle Carlisle ( , ; from xcb, Caer Luel) is a city that lies within the Northern English county of Cumbria, south of the Scottish border at the confluence of the rivers Eden, Caldew and Petteril. It is the administrative centre of the City ...
. The
Commonwealth of Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, Ma ...
refers to the turnpike as the Granddaddy of the Pikes (referring to
turnpike Turnpike often refers to: * A type of gate, another word for a turnstile * In the United States, a toll road Turnpike may also refer to: Roads United Kingdom * A turnpike road, a principal road maintained by a turnpike trust, a body with powe ...
s). Milestones in the construction of the Interstate Highway System include: * October 17, 1974:
Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the sout ...
becomes the first state to complete all of its mainline Interstate Highways with the dedication of its final piece of
I-80 Interstate 80 (I-80) is an east–west transcontinental freeway that crosses the United States from downtown San Francisco, California, to Teaneck, New Jersey, in the New York metropolitan area. The highway was designated in 1956 as one o ...
. * October 12, 1979: The final section of the Canada to Mexico freeway
Interstate 5 Interstate 5 (I-5) is the main north–south Interstate Highway on the West Coast of the United States, running largely parallel to the Pacific coast of the contiguous U.S. from Mexico to Canada. It travels through the states of Californi ...
is dedicated near
Stockton, California Stockton is a city in and the county seat of San Joaquin County in the Central Valley of the U.S. state of California. Stockton was founded by Carlos Maria Weber in 1849 after he acquired Rancho Campo de los Franceses. The city is named after R ...
. Representatives of the two neighboring nations attended the dedication to commemorate the first contiguous freeway connecting the North American countries. * August 22, 1986: The final section of the coast-to-coast
I-80 Interstate 80 (I-80) is an east–west transcontinental freeway that crosses the United States from downtown San Francisco, California, to Teaneck, New Jersey, in the New York metropolitan area. The highway was designated in 1956 as one o ...
(
San Francisco, California San Francisco (; Spanish for " Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the fourth most populous in California and 17t ...
, to
Teaneck, New Jersey Teaneck () is a township in Bergen County, in the U.S. state of New Jersey. It is a bedroom community in the New York metropolitan area. As of the 2010 U.S. census, the township's population was 39,776, reflecting an increase of 516 (+1.3%) f ...
) is dedicated on the western edge of
Salt Lake City, Utah Salt Lake City (often shortened to Salt Lake and abbreviated as SLC) is the capital and most populous city of Utah, United States. It is the seat of Salt Lake County, the most populous county in Utah. With a population of 200,133 in 2020, t ...
, making I-80 the world's first contiguous freeway to span from the Atlantic to Pacific Ocean and, at the time, the longest contiguous freeway in the world. The section spanned from
Redwood Road State Route 68 (SR-68) is a state highway in the U.S. state of Utah. It is a major thoroughfare throughout the Wasatch Front as it runs north–south for , linking US-6 near Elberta to US-89 in Woods Cross. The route intersects several m ...
to just west of the
Salt Lake City International Airport Salt Lake City International Airport is a civil-military airport located about west of Downtown Salt Lake City, Utah, in the United States. The airport is the closest commercial airport for more than 2.5 million people and is within a 30-min ...
. At the dedication it was noted that coincidentally this was only from
Promontory Summit Promontory is an area of high ground in Box Elder County, Utah, United States, 32 mi (51 km) west of Brigham City and 66 mi (106 km) northwest of Salt Lake City. Rising to an elevation of 4,902 feet (1,494 m) above sea ...
, where a similar feat was accomplished nearly 120 years prior, the driving of the
golden spike The golden spike (also known as The Last Spike) is the ceremonial 17.6- karat gold final spike driven by Leland Stanford to join the rails of the first transcontinental railroad across the United States connecting the Central Pacific Railroad ...
of the United States'
First transcontinental railroad North America's first transcontinental railroad (known originally as the "Pacific Railroad" and later as the " Overland Route") was a continuous railroad line constructed between 1863 and 1869 that connected the existing eastern U.S. rail netwo ...
. * August 10, 1990: The final section of coast-to-coast
I-10 Interstate 10 (I-10) is the southernmost cross-country highway in the American Interstate Highway System. I-10 is the fourth-longest Interstate in the United States at , following I-90, I-80, and I-40. This freeway is part of the originally p ...
(
Santa Monica, California Santa Monica (; Spanish: ''Santa Mónica'') is a city in Los Angeles County, situated along Santa Monica Bay on California's South Coast. Santa Monica's 2020 U.S. Census population was 93,076. Santa Monica is a popular resort town, owing to ...
, to
Jacksonville, Florida Jacksonville is a city located on the Atlantic coast of northeast Florida, the most populous city proper in the state and is the largest city by area in the contiguous United States as of 2020. It is the seat of Duval County, with which th ...
) is dedicated, the
Papago Freeway Tunnel The Papago Freeway Tunnel, better known to Phoenix residents as the Deck Park Tunnel, is a vehicular underpass built underneath Downtown Phoenix. It was built as part of Interstate Highway 10 in Phoenix, Arizona. Route The underpass extends fr ...
under downtown
Phoenix, Arizona Phoenix ( ; nv, Hoozdo; es, Fénix or , yuf-x-wal, Banyà:nyuwá) is the List of capitals in the United States, capital and List of cities and towns in Arizona#List of cities and towns, most populous city of the U.S. state of Arizona, with 1 ...
. Completion of this section was delayed due to a
freeway revolt Highway revolts (also freeway revolts, expressway revolts, or road protests) are organized protests against the planning or construction of highways, freeways, expressways, and other civil engineering projects that favor vehicles. Many freeway r ...
that forced the cancellation of an originally planned elevated routing. * September 12, 1991:
I-90 Interstate 90 (I-90) is an east–west transcontinental freeway and the longest Interstate Highway in the United States at . It begins in Seattle, Washington, and travels through the Pacific Northwest, Mountain West, Great Plains, Midwest, an ...
becomes the final coast-to-coast Interstate Highway (
Seattle, Washington Seattle ( ) is a seaport city on the West Coast of the United States. It is the seat of King County, Washington. With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest region ...
to Boston, Massachusetts) to be completed with the dedication of an elevated
viaduct A viaduct is a specific type of bridge that consists of a series of arches, piers or columns supporting a long elevated railway or road. Typically a viaduct connects two points of roughly equal elevation, allowing direct overpass across a wide v ...
bypassing
Wallace, Idaho Wallace, Idaho is a city in and the county seat of Shoshone County, Idaho, in the Silver Valley mining district of the Idaho Panhandle. Founded in 1884, Wallace sits alongside the South Fork of the Coeur d'Alene River (and Interstate 90), app ...
. This section was delayed after residents forced the cancellation of the originally planned at-grade alignment that would have demolished much of downtown Wallace. The residents accomplished this feat by arranging for most of the downtown area to be declared a
historic district A historic district or heritage district is a section of a city which contains older buildings considered valuable for historical or architectural reasons. In some countries or jurisdictions, historic districts receive legal protection from cer ...
and listed on the
National Register of Historic Places The National Register of Historic Places (NRHP) is the United States federal government's official list of districts, sites, buildings, structures and objects deemed worthy of preservation for their historical significance or "great artistic ...
; this succeeded in blocking the path of the original alignment. After the dedication residents held a mock funeral celebrating the removal of the last stoplight on a transcontinental Interstate Highway. * October 14, 1992: The original Interstate Highway System is proclaimed to be complete with the opening of
I-70 Interstate 70 (I-70) is a major east–west Interstate Highway in the United States that runs from I-15 near Cove Fort, Utah, to a park and ride lot just east of I-695 in Baltimore, Maryland, and is the fifth-longest Interstate in the c ...
through
Glenwood Canyon Glenwood Canyon is a rugged scenic canyon in western Colorado in the United States. Its walls climb as high as above the Colorado River. It is the largest such canyon on the Upper Colorado. The canyon, which has historically provided the route ...
in
Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the ...
. This section is considered an engineering marvel with a span featuring 40 bridges and numerous tunnels and is one of the most expensive rural highways per mile built in the United States. The initial cost estimate for the system was $25 billion over 12 years; it ended up costing $114 billion (equivalent to $425 billion in 2006 or $ in ) and took 35 years.


1992–present


Discontinuities

The system was proclaimed complete in 1992, but two of the original Interstates—
I-95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from US Route 1 (US 1) in Miami, Florida, to the Houlton–Woodstock Border Crossing between Maine and the Canadia ...
and
I-70 Interstate 70 (I-70) is a major east–west Interstate Highway in the United States that runs from I-15 near Cove Fort, Utah, to a park and ride lot just east of I-695 in Baltimore, Maryland, and is the fifth-longest Interstate in the c ...
—were not continuous: both of these discontinuities were due to local opposition, which blocked efforts to build the necessary connections to fully complete the system. I-95 was made a continuous freeway in 2018, and thus I-70 remains the only original Interstate with a discontinuity. I-95 was discontinuous in New Jersey because of the cancellation of the
Somerset Freeway Interstate 95 (I-95) is a major Interstate Highway that traverses nearly the full extent of the East Coast of the United States, from Florida to Maine. In the state of New Jersey, it runs along much of the mainline of the New Jersey Turnpike ( ...
. This situation was remedied when the construction of the
Pennsylvania Turnpike/Interstate 95 Interchange Project The Pennsylvania Turnpike/Interstate 95 Interchange Project is an ongoing road construction project to build an interchange where Interstate 95 (I-95) crosses the Pennsylvania Turnpike in Bristol Township, Bucks County, Pennsylvania, in the U ...
started in 2010 and partially opened on September 22, 2018, which was already enough to fill the gap. However, I-70 remains discontinuous in
Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
, because of the lack of a direct interchange with the
Pennsylvania Turnpike The Pennsylvania Turnpike (Penna Turnpike or PA Turnpike) is a toll highway operated by the Pennsylvania Turnpike Commission (PTC) in the U.S. state of Pennsylvania. A controlled-access highway, it runs for across the state. The turnpike's we ...
at the eastern end of the concurrency near Breezewood. Traveling in either direction, I-70 traffic must exit the freeway and use a short stretch of US-30 (which includes a number of roadside services) to rejoin I-70. The interchange was not originally built because of a legacy federal funding rule, since relaxed, which restricted the use of federal funds to improve roads financed with tolls. Solutions have been proposed to eliminate the discontinuity, but they have been blocked by local opposition, fearing a loss of business.


Expansion

The Interstate Highway System has been expanded numerous times. The expansions have both created new designations and extended existing designations. For example,
I-49 Interstate 49 (I-49) is a north–south Interstate Highway that exists in multiple segments: the original portion entirely within the state of Louisiana with an additional signed portion extending from I-220 in Shreveport to the Arkansas s ...
, added to the system in the 1980s as a freeway in
Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is bord ...
, was designated as an expansion corridor, and FHWA approved the expanded route north from
Lafayette, Louisiana Lafayette (, ) is a city in the U.S. state of Louisiana, and the most populous city and parish seat of Lafayette Parish, located along the Vermilion River. It is Louisiana's fourth largest incorporated municipality by population and the 234t ...
, to
Kansas City, Missouri Kansas City (abbreviated KC or KCMO) is the largest city in Missouri by population and area. As of the 2020 United States census, 2020 census, the city had a population of 508,090 in 2020, making it the List of United States cities by populat ...
. The freeway exists today as separate completed segments, with segments under construction or in the planning phase between them. In 1966, the FHWA designated the entire Interstate Highway System as part of the larger
Pan-American Highway The Pan-American Highway (french: (Auto)route panaméricaine/transaméricaine; pt, Rodovia/Auto-estrada Pan-americana; es, Autopista/Carretera/Ruta Panamericana) is a network of roads stretching across the Americas and measuring about in to ...
System, and at least two proposed Interstate expansions were initiated to help trade with Canada and Mexico spurred by the
North American Free Trade Agreement The North American Free Trade Agreement (NAFTA ; es, Tratado de Libre Comercio de América del Norte, TLCAN; french: Accord de libre-échange nord-américain, ALÉNA) was an agreement signed by Canada, Mexico, and the United States that crea ...
(NAFTA). Long-term plans for
I-69 Interstate 69 (I-69) is an Interstate Highway in the United States currently consisting of 10 unconnected segments with an original continuous segment from Indianapolis, Indiana, northeast to the Canadian border in Port Huron, Michigan, at ...
, which currently exists in several separate completed segments (the largest of which are in
Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th ...
and
Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
), is to have the highway route extend from
Tamaulipas Tamaulipas (), officially the Free and Sovereign State of Tamaulipas ( es, Estado Libre y Soberano de Tamaulipas), is a state in the northeast region of Mexico; one of the 31 states which, along with Mexico City, comprise the 32 Federal Entiti ...
, Mexico to
Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...
, Canada. The planned I-11 will then bridge the Interstate gap between
Phoenix, Arizona Phoenix ( ; nv, Hoozdo; es, Fénix or , yuf-x-wal, Banyà:nyuwá) is the List of capitals in the United States, capital and List of cities and towns in Arizona#List of cities and towns, most populous city of the U.S. state of Arizona, with 1 ...
and
Las Vegas, Nevada Las Vegas (; Spanish for "The Meadows"), often known simply as Vegas, is the 25th-most populous city in the United States, the most populous city in the state of Nevada, and the county seat of Clark County. The city anchors the Las Vega ...
, and thus form part of the
CANAMEX Corridor The CANAMEX corridor is a series of improvements to freeways and other transportation infrastructure linking Canada to Mexico through the United States. The corridor was established under the North American Free Trade Agreement. Currently the corr ...
(along with I-19, and portions of
I-10 Interstate 10 (I-10) is the southernmost cross-country highway in the American Interstate Highway System. I-10 is the fourth-longest Interstate in the United States at , following I-90, I-80, and I-40. This freeway is part of the originally p ...
and
I-15 I15 may refer to: * Interstate 15, a north–south Interstate Highway in the United States of America * Polikarpov I-15, a Soviet fighter aircraft * I15 (band) "Soulja Girl" is the second single from American rapper Soulja Boy's studio album '' ...
) between
Sonora Sonora (), officially Estado Libre y Soberano de Sonora ( en, Free and Sovereign State of Sonora), is one of the 31 states which, along with Mexico City, comprise the Federal Entities of Mexico. The state is divided into 72 municipalities; the ...
, Mexico and
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest T ...
, Canada.


Urban Interstates abandoned because of local opposition

Political opposition from residents canceled many freeway projects around the United States, including: *
I-40 Interstate 40 (I-40) is a major east–west Interstate Highway running through the south-central portion of the United States. At a length of , it is the third-longest Interstate Highway in the country, after I-90 and I-80. From west to ea ...
in Memphis, Tennessee was rerouted and part of the original I-40 is still in use as the eastern half of
Sam Cooper Boulevard Sam Cooper Boulevard is an urban highway in Memphis, Tennessee, United States. The more recent western segment of the road follows a parkway design, while the older eastern portion, which was proposed and constructed as a segment of Interstate 4 ...
. * I-66 in the
District of Columbia ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle (Washington, D.C.), Logan Circle, Jefferson Memoria ...
was abandoned in 1977. *
I-69 Interstate 69 (I-69) is an Interstate Highway in the United States currently consisting of 10 unconnected segments with an original continuous segment from Indianapolis, Indiana, northeast to the Canadian border in Port Huron, Michigan, at ...
was to continue past its terminus at Interstate 465 to intersect with
Interstate 70 Interstate 70 (I-70) is a major east–west Interstate Highway in the United States that runs from I-15 near Cove Fort, Utah, to a park and ride lot just east of I-695 in Baltimore, Maryland, and is the fifth-longest Interstate in the co ...
and
Interstate 65 Interstate 65 (I-65) is a major north–south Interstate Highway in the central United States. As with most primary Interstates ending in 5, it is a major crosscountry, north–south route, connecting between the Great Lakes and the Gul ...
at the north split, northeast of downtown
Indianapolis Indianapolis (), colloquially known as Indy, is the state capital and most populous city of the U.S. state of Indiana and the seat of Marion County. According to the U.S. Census Bureau, the consolidated population of Indianapolis and Marion ...
. Though local opposition led to the cancellation of this project in 1981, bridges and ramps for the connection into the "north split" remain visible. *
I-70 Interstate 70 (I-70) is a major east–west Interstate Highway in the United States that runs from I-15 near Cove Fort, Utah, to a park and ride lot just east of I-695 in Baltimore, Maryland, and is the fifth-longest Interstate in the c ...
in
Baltimore Baltimore ( , locally: or ) is the most populous city in the U.S. state of Maryland, fourth most populous city in the Mid-Atlantic, and the 30th most populous city in the United States with a population of 585,708 in 2020. Baltimore was ...
was supposed to run from the Baltimore Beltway ( Interstate 695), which surrounds the city to terminate at
I-95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from US Route 1 (US 1) in Miami, Florida, to the Houlton–Woodstock Border Crossing between Maine and the Canadia ...
, the East Coast thoroughfare that runs through Maryland and Baltimore on a diagonal course, northeast to southwest; the connection was cancelled on the mid-1970s due to its routing through Gwynns Falls-Leakin Park, a wilderness urban park reserve following the
Gwynns Falls Gwynns Falls is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed April 1, 2011. stream located in Baltimore County and Baltimore City, Maryland. Its headwaters are located in Reisterstow ...
stream through West Baltimore. This included the cancellation of I-170, partially built and in use as U.S. Route 40, and nicknamed the Highway to Nowhere. *
I-78 Interstate 78 (I-78) is an east–west Interstate Highway in the Northeastern United States, running from I-81 northeast of Harrisburg, Pennsylvania, through Allentown to western and northern New Jersey and terminating at the Holland T ...
in New York City was canceled along with portions of
I-278 Interstate 278 (I-278) is an auxiliary Interstate Highway in New Jersey and New York in the United States. The road runs from US Route 1/9 (US 1/9) in Linden, New Jersey, northeast to the Bruckner Interchange in the New York ...
, I-478, and I-878 (now designated as New York State Route 878). I-878 was supposed to be part of I-78, and I-478 and I-278 were to be spur routes. *
I-80 Interstate 80 (I-80) is an east–west transcontinental freeway that crosses the United States from downtown San Francisco, California, to Teaneck, New Jersey, in the New York metropolitan area. The highway was designated in 1956 as one o ...
in San Francisco was originally planned to travel past the city's Civic Center along the Panhandle Freeway into
Golden Gate Park Golden Gate Park, located in San Francisco, California, United States, is a large urban park consisting of of public grounds. It is administered by the San Francisco Recreation & Parks Department, which began in 1871 to oversee the developm ...
and terminate at the original alignment of I-280/ SR 1. The city canceled this and several other freeways in 1958. Similarly, more than 20 years later, Sacramento canceled plans to upgrade I-80 to Interstate Standards and rerouted the freeway on what was then I-880 that traveled north of Downtown Sacramento. *
I-83 Interstate 83 (I-83) is an Interstate Highway in the Eastern United States. Its southern terminus is at a signalized intersection with Fayette Street in Baltimore, Maryland; its northern terminus is at I-81 near Harrisburg, Pennsylvania. Mo ...
, southern extension of the Jones Falls Expressway (southern
I-83 Interstate 83 (I-83) is an Interstate Highway in the Eastern United States. Its southern terminus is at a signalized intersection with Fayette Street in Baltimore, Maryland; its northern terminus is at I-81 near Harrisburg, Pennsylvania. Mo ...
) in
Baltimore Baltimore ( , locally: or ) is the most populous city in the U.S. state of Maryland, fourth most populous city in the Mid-Atlantic, and the 30th most populous city in the United States with a population of 585,708 in 2020. Baltimore was ...
was supposed to run along the waterfront of the
Patapsco River The Patapsco River mainstem is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map , accessed April 1, 2011 river in central Maryland that flows into the Chesapeake Bay. The river's tidal port ...
/
Baltimore Harbor Helen Delich Bentley Port of Baltimore is a shipping port along the tidal basins of the three branches of the Patapsco River in Baltimore, Maryland on the upper northwest shore of the Chesapeake Bay. It is the nation's largest port facilities fo ...
to connect to
I-95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from US Route 1 (US 1) in Miami, Florida, to the Houlton–Woodstock Border Crossing between Maine and the Canadia ...
, bisecting historic neighborhoods of
Fells Point Fell's Point is a historic waterfront neighborhood in southeastern Baltimore, Maryland. It was established around 1763 along the north shore of the Baltimore Harbor and the Northwest Branch of the Patapsco River. The area has many antique, music, ...
and
Canton Canton may refer to: Administrative division terminology * Canton (administrative division), territorial/administrative division in some countries, notably Switzerland * Township (Canada), known as ''canton'' in Canadian French Arts and ente ...
, but the connection was never built. *
I-84 Interstate 84 may refer to: * Interstate 84 (Oregon–Utah), passing through Idaho, formerly known as Interstate 80N * Interstate 84 (Pennsylvania–Massachusetts) Interstate 84 (I-84) is an Interstate Highway in the Northeaster ...
in
Connecticut Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York (state), New York to the west, and Long Island Sound to the ...
was once planned to fork east of Hartford, into an
I-86 Interstate 86 may refer to any of three unconnected Interstate Highways in the United States: * Interstate 86 (Pennsylvania–New York) * Interstate 86 (Idaho) * Interstate 84 (Pennsylvania–Massachusetts) Interstate 84 (I-84) is an I ...
to Sturbridge, Massachusetts, and I-84 to Providence, R.I. The plan was cancelled, primarily because of anticipated impact on a major Rhode Island reservoir. The I-84 designation was restored to the highway to Sturbridge, and other numbering was used for completed Eastern sections of what had been planned as part of I-84. *
I-95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from US Route 1 (US 1) in Miami, Florida, to the Houlton–Woodstock Border Crossing between Maine and the Canadia ...
through the
District of Columbia ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle (Washington, D.C.), Logan Circle, Jefferson Memoria ...
into
Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean t ...
was abandoned in 1977. Instead it was rerouted to I-495 (Capital Beltway). The completed section is now
I-395 Interstate 395 may refer to: * Interstate 395 (Connecticut–Massachusetts), a spur from I-95 to Auburn, Massachusetts *Interstate 395 (Delaware), a proposed portion of I-95 in Delaware, when it was under construction *Interstate 395 (Florida), a sp ...
. *
I-95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from US Route 1 (US 1) in Miami, Florida, to the Houlton–Woodstock Border Crossing between Maine and the Canadia ...
was originally planned to run up the Southwest Expressway and meet
I-93 Interstate 93 (I-93) is an Interstate Highway in the New England states of Massachusetts, New Hampshire, and Vermont in the United States. Spanning approximately along a north–south axis, it is one of three primary Interstate Highways ...
, where the two highways would travel along the
Central Artery The Central Artery (officially the John F. Fitzgerald Expressway) is a section of freeway in downtown Boston, Massachusetts; it is designated as Interstate 93, US 1 and Route 3. The original Artery, constructed in the 1950s, was named aft ...
through downtown
Boston Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- mo ...
, but was rerouted onto the
Route 128 The following highways are numbered 128: Canada * New Brunswick Route 128 * Ontario Highway 128 (former) * Prince Edward Island Route 128 Costa Rica * National Route 128 India * National Highway 128 (India) Japan * Japan National Route 128 ...
beltway due to widespread opposition. This revolt also included the cancellation of the Inner Belt, connecting I-93 to
I-90 Interstate 90 (I-90) is an east–west transcontinental freeway and the longest Interstate Highway in the United States at . It begins in Seattle, Washington, and travels through the Pacific Northwest, Mountain West, Great Plains, Midwest, an ...
and a cancelled section of the Northwest Expressway which would have carried US 3 inside the Route 128 beltway, meeting with
Route 2 The following highways are numbered 2. For roads numbered A2, see list of A2 roads. For roads numbered B2, see list of B2 roads. For roads numbered M2, see list of M2 roads. For roads numbered N2, see list of N2 roads. International * AH2, As ...
in
Cambridge Cambridge ( ) is a university city and the county town in Cambridgeshire, England. It is located on the River Cam approximately north of London. As of the 2021 United Kingdom census, the population of Cambridge was 145,700. Cambridge bec ...
.


Standards

The
American Association of State Highway and Transportation Officials The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test protocols, and guidelines that are used in highway design and construction throughout the United ...
(AASHTO) has defined a set of standards that all new Interstates must meet unless a waiver from the
Federal Highway Administration The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program ...
(FHWA) is obtained. One almost absolute standard is the
controlled access A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms ...
nature of the roads. With few exceptions,
traffic light Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control flows of traffic. Traffic light ...
s (and cross traffic in general) are limited to toll booths and
ramp meter A ramp meter, ramp signal, or metering light is a device, usually a basic traffic light or a two-section signal light (red and green only, no yellow) together with a signal controller, that regulates the flow of traffic entering freeways accordi ...
s (metered flow control for lane merging during
rush hour A rush hour (American English, British English) or peak hour (Australian English) is a part of the day during which traffic congestion on roads and crowding on public transport is at its highest. Normally, this happens twice every weekday: o ...
).


Speed limits

Being
freeway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms ...
s, Interstate Highways usually have the highest
speed limit Speed limits on road traffic, as used in most countries, set the legal maximum speed at which vehicles may travel on a given stretch of road. Speed limits are generally indicated on a traffic sign reflecting the maximum permitted speed - expre ...
s in a given area. Speed limits are determined by individual states. From 1975 to 1986, the maximum speed limit on any highway in the United States was , in accordance with federal law. Typically, lower limits are established in Northeastern and coastal states, while higher speed limits are established in inland states west of the
Mississippi River The Mississippi River is the List of longest rivers of the United States (by main stem), second-longest river and chief river of the second-largest Drainage system (geomorphology), drainage system in North America, second only to the Hudson B ...
. For example, the maximum speed limit is in northern Maine, varies between from southern Maine to New Jersey, and is in New York City and the District of Columbia. Currently, rural speed limits elsewhere generally range from . Several portions of various highways such as
I-10 Interstate 10 (I-10) is the southernmost cross-country highway in the American Interstate Highway System. I-10 is the fourth-longest Interstate in the United States at , following I-90, I-80, and I-40. This freeway is part of the originally p ...
and
I-20 Interstate 20 (I‑20) is a major east–west Interstate Highway in the Southern United States. I-20 runs beginning at an interchange with I-10 in Scroggins Draw, Texas, and ending at an interchange with I-95 in Florence, South Carolina. Betwe ...
in rural western Texas,
I-80 Interstate 80 (I-80) is an east–west transcontinental freeway that crosses the United States from downtown San Francisco, California, to Teaneck, New Jersey, in the New York metropolitan area. The highway was designated in 1956 as one o ...
in Nevada between Fernley and Winnemucca (except around Lovelock) and portions of
I-15 I15 may refer to: * Interstate 15, a north–south Interstate Highway in the United States of America * Polikarpov I-15, a Soviet fighter aircraft * I15 (band) "Soulja Girl" is the second single from American rapper Soulja Boy's studio album '' ...
,
I-70 Interstate 70 (I-70) is a major east–west Interstate Highway in the United States that runs from I-15 near Cove Fort, Utah, to a park and ride lot just east of I-695 in Baltimore, Maryland, and is the fifth-longest Interstate in the c ...
,
I-80 Interstate 80 (I-80) is an east–west transcontinental freeway that crosses the United States from downtown San Francisco, California, to Teaneck, New Jersey, in the New York metropolitan area. The highway was designated in 1956 as one o ...
, and
I-84 Interstate 84 may refer to: * Interstate 84 (Oregon–Utah), passing through Idaho, formerly known as Interstate 80N * Interstate 84 (Pennsylvania–Massachusetts) Interstate 84 (I-84) is an Interstate Highway in the Northeaster ...
in Utah have a speed limit of . Other Interstates in Idaho, Montana, Oklahoma, South Dakota and Wyoming also have the same high speed limits. In some areas, speed limits on Interstates can be significantly lower in areas where they traverse significantly hazardous areas. The maximum speed limit on
I-90 Interstate 90 (I-90) is an east–west transcontinental freeway and the longest Interstate Highway in the United States at . It begins in Seattle, Washington, and travels through the Pacific Northwest, Mountain West, Great Plains, Midwest, an ...
is in downtown
Cleveland Cleveland ( ), officially the City of Cleveland, is a city in the United States, U.S. U.S. state, state of Ohio and the county seat of Cuyahoga County, Ohio, Cuyahoga County. Located in the northeastern part of the state, it is situated along ...
because of two sharp curves with a suggested limit of in a heavily congested area;
I-70 Interstate 70 (I-70) is a major east–west Interstate Highway in the United States that runs from I-15 near Cove Fort, Utah, to a park and ride lot just east of I-695 in Baltimore, Maryland, and is the fifth-longest Interstate in the c ...
through
Wheeling, West Virginia Wheeling is a city in the U.S. state of West Virginia. Located almost entirely in Ohio County, of which it is the county seat, it lies along the Ohio River in the foothills of the Appalachian Mountains and also contains a tiny portion extending ...
, has a maximum speed limit of through the
Wheeling Tunnel The Wheeling Tunnel is a set of twin tunnels named for and located in Wheeling, West Virginia. The tunnels are long each, cutting through Wheeling Hill, and each carries two lanes of Interstate 70 and U.S. Route 250. The tunnels originally to ...
and most of downtown Wheeling; and
I-68 Interstate 68 (I-68) is a Interstate Highway in the US states of West Virginia and Maryland, connecting I-79 in Morgantown, West Virginia, to I-70 in Hancock, Maryland. I-68 is also Corridor E of the Appalachian Development Highway Syst ...
has a maximum speed limit of through
Cumberland, Maryland Cumberland is a U.S. city in and the county seat of Allegany County, Maryland. It is the primary city of the Cumberland, MD-WV Metropolitan Statistical Area. At the 2020 census, the city had a population of 19,076. Located on the Potomac River, ...
, because of multiple hazards including sharp curves and narrow lanes through the city. In some locations, low speed limits are the result of lawsuits and resident demands; after holding up the completion of
I-35E Interstate 35E may refer to: *Interstate 35E (Texas), a long branch route serving Dallas, Texas *Interstate 35E (Minnesota), a long branch route serving St. Paul, Minnesota See also * Interstate 35W (disambiguation) Interstate 35W may refer to: * ...
in
St. Paul, Minnesota Saint Paul (abbreviated St. Paul) is the capital of the U.S. state of Minnesota and the county seat of Ramsey County. Situated on high bluffs overlooking a bend in the Mississippi River, Saint Paul is a regional business hub and the center o ...
, for nearly 30 years in the courts, residents along the stretch of the freeway from the southern city limit to downtown successfully lobbied for a speed limit in addition to a prohibition on any vehicle weighing more than
gross vehicle weight Vehicle weight is a measurement of wheeled motor vehicles; either an actual measured weight of the vehicle under defined conditions or a gross weight rating for its weight carrying capacity. Curb or kerb weight Curb weight (U.S. English) or kerb ...
.
I-93 Interstate 93 (I-93) is an Interstate Highway in the New England states of Massachusetts, New Hampshire, and Vermont in the United States. Spanning approximately along a north–south axis, it is one of three primary Interstate Highways ...
in Franconia Notch State Park in northern New Hampshire has a speed limit of because it is a parkway that consists of only one lane per side of the highway. On the other hand, Interstates 15, 80, 84, and 215 in Utah have speed limits as high as within the
Wasatch Front The Wasatch Front is a metropolitan region in the north-central part of the U.S. state of Utah. It consists of a chain of contiguous cities and towns stretched along the Wasatch Range from approximately Provo in the south to Logan in the nort ...
,
Cedar City Cedar City is the largest city in Iron County, Utah, United States. It is located south of Salt Lake City, and north of Las Vegas on Interstate 15. It is the home of Southern Utah University, the Utah Shakespeare Festival, the Utah Summer Gam ...
, and St. George areas, and
I-25 Interstate 25 (I-25) is a major Interstate Highway in the western United States. It is primarily a north–south highway, serving as the main route through New Mexico, Colorado, and Wyoming. I-25 stretches from I-10 at Las Cruces, New Mexic ...
in New Mexico within the Santa Fe and
Las Vegas Las Vegas (; Spanish for "The Meadows"), often known simply as Vegas, is the 25th-most populous city in the United States, the most populous city in the state of Nevada, and the county seat of Clark County. The city anchors the Las Veg ...
areas along with
I-20 Interstate 20 (I‑20) is a major east–west Interstate Highway in the Southern United States. I-20 runs beginning at an interchange with I-10 in Scroggins Draw, Texas, and ending at an interchange with I-95 in Florence, South Carolina. Betwe ...
in Texas along Odessa and Midland and
I-29 Interstate 29 (I-29) is an Interstate Highway in the Midwestern United States. I-29 runs from Kansas City, Missouri, at a junction with I-35 and I-70, to the Canada–US border near Pembina, North Dakota, where it connects with Manitoba ...
in North Dakota along the
Grand Forks Grand Forks is the third-largest city in the state of North Dakota (after Fargo and Bismarck) and the county seat of Grand Forks County. According to the 2020 census, the city's population was 59,166. Grand Forks, along with its twin city ...
area have higher speed limits of .


Other uses

As one of the components of the National Highway System, Interstate Highways improve the mobility of military troops to and from airports, seaports, rail terminals, and other military bases. Interstate Highways also connect to other roads that are a part of the
Strategic Highway Network The National Highway System (NHS) is a network of strategic highways within the United States, including the Interstate Highway System and other roads serving major airports, ports, military bases, rail or truck terminals, railway stations, pip ...
, a system of roads identified as critical to the
U.S. Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national secur ...
. The system has also been used to facilitate evacuations in the face of hurricanes and other natural disasters. An option for maximizing traffic throughput on a highway is to reverse the flow of traffic on one side of a divider so that all lanes become outbound lanes. This procedure, known as
contraflow lane reversal Contraflow lane reversal is the altering of the normal flow of traffic, typically on a controlled-access highway (such as a freeway or motorway), to either aid in an emergency evacuation (the most common usage of the term in the United States) o ...
, has been employed several times for hurricane evacuations. After public outcry regarding the inefficiency of evacuating from southern Louisiana prior to
Hurricane Georges Hurricane Georges () was a powerful and long-lived Cape Verde Category 4 hurricane which caused severe destruction as it traversed the Caribbean and Gulf of Mexico in September 1998, making eight landfalls along its path. Georges was the seventh ...
' landfall in September 1998, government officials looked towards contraflow to improve evacuation times. In
Savannah, Georgia Savannah ( ) is the oldest city in the U.S. state of Georgia (U.S. state), Georgia and is the county seat of Chatham County, Georgia, Chatham County. Established in 1733 on the Savannah River, the city of Savannah became the Kingdom of Great Br ...
, and
Charleston, South Carolina Charleston is the largest city in the U.S. state of South Carolina, the county seat of Charleston County, and the principal city in the Charleston–North Charleston metropolitan area. The city lies just south of the geographical midpoint o ...
, in 1999, lanes of
I-16 I16 may refer to: * Interstate 16, an interstate highway in the U.S. state of Georgia * Polikarpov I-16, a Soviet fighter aircraft introduced in the 1930s * Halland Regiment * , a Japanese Type C submarine * i16, a name for the 16-bit signed integ ...
and
I-26 I26 may refer to: * Interstate 26, a road in the United States of America * {{Letter-NumberCombDisambig ...
were used in a contraflow configuration in anticipation of
Hurricane Floyd Hurricane Floyd was a very powerful Cape Verde hurricane which struck the Bahamas and the East Coast of the United States. It was the sixth named storm, fourth hurricane, and third major hurricane in the 1999 Atlantic hurricane season. Floyd tr ...
with mixed results. In 2004 contraflow was employed ahead of
Hurricane Charley Hurricane Charley was the first of four separate hurricanes to impact or strike Florida during 2004, along with Frances, Ivan and Jeanne, as well as one of the strongest hurricanes ever to strike the United States. It was the third named s ...
in the
Tampa, Florida Tampa () is a city on the Gulf Coast of the U.S. state of Florida. The city's borders include the north shore of Tampa Bay and the east shore of Old Tampa Bay. Tampa is the largest city in the Tampa Bay area and the seat of Hillsborough ...
area and on the
Gulf Coast The Gulf Coast of the United States, also known as the Gulf South, is the coast, coastline along the Southern United States where they meet the Gulf of Mexico. The list of U.S. states and territories by coastline, coastal states that have a shor ...
before the landfall of
Hurricane Ivan Hurricane Ivan was a large, long-lived, Cape Verde hurricane that caused widespread damage in the Caribbean and United States. The cyclone was the ninth named storm, the sixth hurricane and the fourth major hurricane of the active 2004 Atlant ...
; however, evacuation times there were no better than previous evacuation operations. Engineers began to apply lessons learned from the analysis of prior contraflow operations, including limiting exits, removing troopers (to keep traffic flowing instead of having drivers stop for directions), and improving the dissemination of public information. As a result, the 2005 evacuation of New Orleans, Louisiana, prior to
Hurricane Katrina Hurricane Katrina was a destructive Category 5 Atlantic hurricane that caused over 1,800 fatalities and $125 billion in damage in late August 2005, especially in the city of New Orleans and the surrounding areas. It was at the time the cost ...
ran much more smoothly. According to
urban legend An urban legend (sometimes contemporary legend, modern legend, urban myth, or urban tale) is a genre of folklore comprising stories or fallacious claims circulated as true, especially as having happened to a "friend of a friend" or a family m ...
, early regulations required that one out of every five miles of the Interstate Highway System must be built straight and flat, so as to be usable by aircraft during times of war. There is no evidence of this rule being included in any Interstate legislation.


Numbering system


Primary (one- and two-digit) Interstates

The numbering scheme for the Interstate Highway System was developed in 1957 by the American Association of State Highway and Transportation Officials (AASHTO). The association's present numbering policy dates back to August 10, 1973. Within the contiguous United States, primary Interstates—also called main line Interstates or two-digit Interstates—are assigned numbers less than 100. While numerous exceptions do exist, there is a general scheme for numbering Interstates. Primary Interstates are assigned one- or two-digit numbers, while shorter routes (such as spurs, loops, and short connecting roads) are assigned three-digit numbers where the last two digits match the parent route (thus,
I-294 Interstate 294 (I-294) is a tolled auxiliary Interstate Highway in northeastern Illinois. It forms the southern portion of the Tri-State Tollway in Illinois. I-294 runs from South Holland at I-80/ I-94 and Illinois Route 394 (IL 394) to ...
is a loop that connects at both ends to I-94, while
I-787 Interstate 787 (I-787) is an auxiliary Interstate Highway in the US state of New York. I-787 is the main highway for those traveling into and out of downtown Albany. The southern terminus is, per New York traffic data, at the toll plaza ...
is a short spur route attached to I-87). In the numbering scheme for the primary routes, east–west highways are assigned even numbers and north–south highways are assigned odd numbers. Odd route numbers increase from west to east, and even-numbered routes increase from south to north (to avoid confusion with the
U.S. Highways The United States Numbered Highway System (often called U.S. Routes or U.S. Highways) is an integrated network of roads and highways numbered within a nationwide grid in the contiguous United States. As the designation and numbering of these hi ...
, which increase from east to west and north to south). This numbering system usually holds true even if the local direction of the route does not match the compass directions. Numbers
divisible In mathematics, a divisor of an integer n, also called a factor of n, is an integer m that may be multiplied by some integer to produce n. In this case, one also says that n is a multiple of m. An integer n is divisible or evenly divisible by ...
by five are intended to be major arteries among the primary routes, carrying traffic long distances. Primary north–south Interstates increase in number from
I-5 Interstate 5 (I-5) is the main north–south Interstate Highway on the West Coast of the United States, running largely parallel to the Pacific coast of the contiguous U.S. from Mexico to Canada. It travels through the states of Californi ...
between Canada and Mexico along the West Coast to I‑95 between Canada and
Miami, Florida Miami ( ), officially the City of Miami, known as "the 305", "The Magic City", and "Gateway to the Americas", is a coastal metropolis and the county seat of Miami-Dade County in South Florida, United States. With a population of 442,241 at ...
along the East Coast. Major west–east arterial Interstates increase in number from
I-10 Interstate 10 (I-10) is the southernmost cross-country highway in the American Interstate Highway System. I-10 is the fourth-longest Interstate in the United States at , following I-90, I-80, and I-40. This freeway is part of the originally p ...
between
Santa Monica, California Santa Monica (; Spanish: ''Santa Mónica'') is a city in Los Angeles County, situated along Santa Monica Bay on California's South Coast. Santa Monica's 2020 U.S. Census population was 93,076. Santa Monica is a popular resort town, owing to ...
, and
Jacksonville, Florida Jacksonville is a city located on the Atlantic coast of northeast Florida, the most populous city proper in the state and is the largest city by area in the contiguous United States as of 2020. It is the seat of Duval County, with which th ...
, to
I-90 Interstate 90 (I-90) is an east–west transcontinental freeway and the longest Interstate Highway in the United States at . It begins in Seattle, Washington, and travels through the Pacific Northwest, Mountain West, Great Plains, Midwest, an ...
between
Seattle, Washington Seattle ( ) is a seaport city on the West Coast of the United States. It is the seat of King County, Washington. With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest region ...
, and Boston, Massachusetts, with two exceptions. There are no I-50 and I-60, as routes with those numbers would likely pass through states that currently have
U.S. Highways The United States Numbered Highway System (often called U.S. Routes or U.S. Highways) is an integrated network of roads and highways numbered within a nationwide grid in the contiguous United States. As the designation and numbering of these hi ...
with the same numbers, which is generally disallowed under highway administration guidelines. Several two-digit numbers are shared between unconnected road segments at opposite ends of the country for various reasons. Some such highways are incomplete Interstates (such as
I-69 Interstate 69 (I-69) is an Interstate Highway in the United States currently consisting of 10 unconnected segments with an original continuous segment from Indianapolis, Indiana, northeast to the Canadian border in Port Huron, Michigan, at ...
and
I-74 } Interstate 74 (I-74) is an Interstate Highway in the Midwestern and Southeastern United States. Its western end is at an interchange with I-80 in Davenport, Iowa ( Quad Cities); the eastern end of its Midwest segment is at an interch ...
) and some just happen to share route designations (such as
I-76 Interstate 76 may refer to: Interstate Highways in the United States * Interstate 76 (Colorado–Nebraska) * Interstate 76 (Ohio–New Jersey), running through Pennsylvania Video gaming * ''Interstate '76 ''Interstate '76'' is a vehicular c ...
,
I-84 Interstate 84 may refer to: * Interstate 84 (Oregon–Utah), passing through Idaho, formerly known as Interstate 80N * Interstate 84 (Pennsylvania–Massachusetts) Interstate 84 (I-84) is an Interstate Highway in the Northeaster ...
, I‑86, I-87, and
I-88 Interstate 88 may refer to either of two United States Interstate highways: * Interstate 88 (Illinois) Interstate 88 (I-88) is an Interstate Highway in the US state of Illinois that runs from an interchange with I-80 near Silvis and ...
). Some of these were due to a change in the numbering system as a result of a new policy adopted in 1973. Previously, letter-suffixed numbers were used for long spurs off primary routes; for example, western I‑84 was I‑80N, as it went north from I‑80. The new policy stated, "No new divided numbers (such as
I-35W Interstate 35W may refer to: *Interstate 35W (Texas), an Interstate highway serving Fort Worth, Texas, and its suburbs *Interstate 35W (Minnesota), a Interstate highway serving Minneapolis, Minnesota, and its suburbs **The I-35W Mississippi River ...
and
I-35E Interstate 35E may refer to: *Interstate 35E (Texas), a long branch route serving Dallas, Texas *Interstate 35E (Minnesota), a long branch route serving St. Paul, Minnesota See also * Interstate 35W (disambiguation) Interstate 35W may refer to: * ...
, etc.) shall be adopted." The new policy also recommended that existing divided numbers be eliminated as quickly as possible; however, an
I-35W Interstate 35W may refer to: *Interstate 35W (Texas), an Interstate highway serving Fort Worth, Texas, and its suburbs *Interstate 35W (Minnesota), a Interstate highway serving Minneapolis, Minnesota, and its suburbs **The I-35W Mississippi River ...
and
I-35E Interstate 35E may refer to: *Interstate 35E (Texas), a long branch route serving Dallas, Texas *Interstate 35E (Minnesota), a long branch route serving St. Paul, Minnesota See also * Interstate 35W (disambiguation) Interstate 35W may refer to: * ...
still exist in the
Dallas–Fort Worth metroplex The Dallas–Fort Worth metroplex, officially designated Dallas–Fort Worth–Arlington by the U.S. Office of Management and Budget, is a conurbated metropolitan statistical area in the U.S. state of Texas encompassing 11 counties and anchor ...
in Texas, and an
I-35W Interstate 35W may refer to: *Interstate 35W (Texas), an Interstate highway serving Fort Worth, Texas, and its suburbs *Interstate 35W (Minnesota), a Interstate highway serving Minneapolis, Minnesota, and its suburbs **The I-35W Mississippi River ...
and
I-35E Interstate 35E may refer to: *Interstate 35E (Texas), a long branch route serving Dallas, Texas *Interstate 35E (Minnesota), a long branch route serving St. Paul, Minnesota See also * Interstate 35W (disambiguation) Interstate 35W may refer to: * ...
that run through
Minneapolis Minneapolis () is the largest city in Minnesota, United States, and the county seat of Hennepin County. The city is abundant in water, with thirteen lakes, wetlands, the Mississippi River, creeks and waterfalls. Minneapolis has its origin ...
and
Saint Paul Paul; grc, Παῦλος, translit=Paulos; cop, ⲡⲁⲩⲗⲟⲥ; hbo, פאולוס השליח (previously called Saul of Tarsus;; ar, بولس الطرسوسي; grc, Σαῦλος Ταρσεύς, Saũlos Tarseús; tr, Tarsuslu Pavlus; ...
, Minnesota, still exist. Additionally, due to Congressional requirements, three sections of I-69 in southern Texas will be divided into
I-69W Interstate 69W (I-69W) is a relatively short north–south Interstate Highway running through South Texas in the United States. The freeway begins northeast of the middle of World Trade International Bridge in Laredo and ends at I-35. In ...
, I-69E, and
I-69C Interstate 69C (I-69C) is a north–south freeway running through South Texas. Once complete, the freeway (with connections to Mexican Federal Highway 97) will begin at I-2/ U.S. Highway 83 (US 83) in Pharr and head northward b ...
(for Central). AASHTO policy allows dual numbering to provide continuity between major control points. This is referred to as a concurrency or overlap. For example, I‑75 and I‑85 share the same roadway in
Atlanta Atlanta ( ) is the capital and most populous city of the U.S. state of Georgia. It is the seat of Fulton County, the most populous county in Georgia, but its territory falls in both Fulton and DeKalb counties. With a population of 498,7 ...
; this section, called the
Downtown Connector In Downtown Atlanta, the Downtown Connector or 75/85 (pronounced "seventy-five eighty-five") is the concurrent section of Interstate 75 and Interstate 85 through the core of the city. Beginning at the I-85/ Langford Parkway interchange, ...
, is labeled both I‑75 and I‑85. Concurrencies between Interstate and U.S. Route numbers are also allowed in accordance with AASHTO policy, as long as the length of the concurrency is reasonable. In rare instances, two highway designations sharing the same roadway are signed as traveling in opposite directions; one such
wrong-way concurrency A concurrency in a road network is an instance of one physical roadway bearing two or more different route numbers. When two roadways share the same right-of-way, it is sometimes called a common section or commons. Other terminology for a concur ...
is found between Wytheville and
Fort Chiswell Chiswell , sometimes , is a small village at the southern end of Chesil Beach, in Underhill, on the Isle of Portland in Dorset. It is the oldest settlement on the island, having formerly been known as Chesilton. The small bay at Chiswell is ca ...
, Virginia, where I‑81 north and I‑77 south are equivalent (with that section of road traveling almost due east), as are I‑81 south and I‑77 north.


Auxiliary (three-digit) Interstates

Auxiliary Interstate Highways are circumferential, radial, or spur highways that principally serve
urban area An urban area, built-up area or urban agglomeration is a human settlement with a high population density and infrastructure of built environment. Urban areas are created through urbanization and are categorized by urban morphology as cities ...
s. These types of Interstate Highways are given three-digit route numbers, which consist of a single digit prefixed to the two-digit number of its parent Interstate Highway. Spur routes deviate from their parent and do not return; these are given an odd first digit. Circumferential and radial loop routes return to the parent, and are given an even first digit. Unlike primary Interstates, three-digit Interstates are signed as either east–west or north–south, depending on the general orientation of the route, without regard to the route number. For instance,
I-190 Interstate 190 may refer to the following Interstate Highways in the United States related to Interstate 90: * Interstate 190 (Illinois), a spur into Chicago's O'Hare International Airport *Interstate 190 (Massachusetts), a spur from Worcester to Le ...
in Massachusetts is labeled north–south, while I-195 in New Jersey is labeled east–west. Some looped Interstate routes use inner–outer directions instead of compass directions, when the use of compass directions would create ambiguity. Due to the large number of these routes, auxiliary route numbers may be repeated in different states along the mainline. Some auxiliary highways do not follow these guidelines, however.


Alaska, Hawaii, and Puerto Rico

The Interstate Highway System also extends to
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...
,
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
, and
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and unincorporated ...
, even though they have no direct land connections to any other states or territories. However, their residents still pay federal fuel and tire taxes. The Interstates in Hawaii, all located on the most populous island of
Oahu Oahu () ( Hawaiian: ''Oʻahu'' ()), also known as "The Gathering Place", is the third-largest of the Hawaiian Islands. It is home to roughly one million people—over two-thirds of the population of the U.S. state of Hawaii. The island of O ...
, carry the prefix H. There are three one-digit routes in the state ( H-1, H-2, and H-3) and one auxiliary route ( H-201). These Interstates connect several
military A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...
and
naval A navy, naval force, or maritime force is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake-borne, riverine, littoral, or ocean-borne combat operations and related functions. It inclu ...
bases together, as well as the important communities spread across Oahu, and especially within the urban core of
Honolulu Honolulu (; ) is the capital and largest city of the U.S. state of Hawaii, which is in the Pacific Ocean. It is an unincorporated county seat of the consolidated City and County of Honolulu, situated along the southeast coast of the isla ...
. Both Alaska and Puerto Rico also have public highways that receive 90 percent of their funding from the Interstate Highway program. The Interstates of Alaska and
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and unincorporated ...
are numbered sequentially in order of funding without regard to the rules on odd and even numbers. They also carry the prefixes A and PR, respectively. However, these highways are signed according to their local designations, not their Interstate Highway numbers. Furthermore, these routes were neither planned according to nor constructed to the official
Interstate Highway standards Standards for Interstate Highways in the United States are defined by the American Association of State Highway and Transportation Officials (AASHTO) in the publication ''A Policy on Design Standards: Interstate System''. For a certain highway to ...
.


Mile markers and exit numbers

On one- or two-digit Interstates, the mile marker numbering almost always begins at the southern or western state line. If an Interstate originates within a state, the numbering begins from the location where the road begins in the south or west. As with all guidelines for Interstate routes, however, numerous exceptions exist. Three-digit Interstates with an even first number that form a complete circumferential (circle) bypass around a city feature mile markers that are numbered in a clockwise direction, beginning just west of an Interstate that bisects the circumferential route near a south polar location. In other words, mile marker 1 on
I-465 Interstate 465 (I-465), also known as the USS ''Indianapolis'' Memorial Highway, is the beltway circling Indianapolis, Indiana, United States. It is roughly rectangular in shape and has a perimeter of approximately . It lies almost compl ...
, a route around Indianapolis, is just west of its junction with
I-65 Interstate 65 (I-65) is a major north–south Interstate Highway in the central United States. As with most primary Interstates ending in 5, it is a major crosscountry, north–south route, connecting between the Great Lakes and the Gulf ...
on the south side of Indianapolis (on the south leg of I-465), and mile marker 53 is just east of this same junction. An exception is I-495 in the
Washington metropolitan area The Washington metropolitan area, also commonly referred to as the National Capital Region, is the metropolitan area centered on Washington, D.C. The metropolitan area includes all of Washington, D.C. and parts of the states of Maryland, Virgi ...
, with mileposts increasing counterclockwise because part of that road is also part of
I-95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from US Route 1 (US 1) in Miami, Florida, to the Houlton–Woodstock Border Crossing between Maine and the Canadia ...
. Most Interstate Highways use distance-based
exit numbers An exit number is a number assigned to a road junction, usually an exit from a freeway. It is usually marked on the same sign as the destinations of the exit. In some countries, such as the United States, it is also marked on a sign in the g ...
so that the exit number is the same as the nearest mile marker. If multiple exits occur within the same mile, letter suffixes may be appended to the numbers in alphabetical order starting with A. A small number of Interstate Highways (mostly in the Northeastern United States) use sequential-based exit numbering schemes (where each exit is numbered in order starting with 1, without regard for the mile markers on the road). One Interstate Highway, I-19 in Arizona, is signed with kilometer-based exit numbers. In the state of New York, most Interstate Highways use sequential exit numbering, with some exceptions.


Business routes

AASHTO defines a category of special routes separate from primary and auxiliary Interstate designations. These routes do not have to comply to Interstate construction or limited-access standards but are routes that may be identified and approved by the association. The same route marking policy applies to both US Numbered Highways and Interstate Highways; however,
business route A business route (or business loop, business spur, or city route) in the United States is a short special route connected to a ''parent'' numbered highway at its beginning, then routed through the central business district of a nearby city ...
designations are sometimes used for Interstate Highways. Known as Business Loops and Business Spurs, these routes principally travel through the corporate limits of a city, passing through the central business district when the regular route is directed around the city. They also use a green shield instead of the red and blue shield. An example would be Business Loop Interstate 75 at
Pontiac, Michigan Pontiac ( ') is a city in and the county seat of Oakland County in the U.S. state of Michigan. As of the 2020 census, the city had a total population of 61,606. A northern suburb of Metro Detroit, Pontiac is about northwest of Detroit. Found ...
, which follows surface roads into and through downtown. Sections of BL I-75's routing had been part of US 10 and M-24, predecessors of
I-75 Interstate 75 (I-75) is a major north–south Interstate Highway in the Great Lakes and Southeastern regions of the United States. As with most Interstates that end in 5, it is a major cross-country, north–south route, traveling from St ...
in the area.


Financing

Interstate Highways and their rights-of-way are owned by the state in which they were built. The last federally owned portion of the Interstate System was the
Woodrow Wilson Bridge The Woodrow Wilson Memorial Bridge (also known as the Woodrow Wilson Bridge or the Wilson Bridge) is a bascule bridge that spans the Potomac River between the independent city of Alexandria, Virginia, and Oxon Hill in Prince George's County, ...
on the Washington Capital Beltway. The new bridge was completed in 2009 and is collectively owned by Virginia and Maryland. Maintenance is generally the responsibility of the state department of transportation. However, there are some segments of Interstate owned and maintained by local authorities. About 70 percent of the construction and maintenance costs of Interstate Highways in the United States have been paid through user fees, primarily the
fuel tax A fuel tax (also known as a petrol, gasoline or gas tax, or as a fuel duty) is an excise tax imposed on the sale of fuel. In most countries the fuel tax is imposed on fuels which are intended for transportation. Fuels used to power agricultural v ...
es collected by the federal, state, and local governments. To a much lesser extent they have been paid for by tolls collected on
toll highway A toll road, also known as a turnpike or tollway, is a public or private road (almost always a controlled-access highway in the present day) for which a fee (or '' toll'') is assessed for passage. It is a form of road pricing typically implemente ...
s and bridges. The federal gasoline tax was first imposed in 1932 at one cent per gallon; during the Eisenhower administration, the
Highway Trust Fund The Highway Trust Fund is a transportation fund in the United States which receives money from a federal fuel tax of 18.4 cents per gallon on gasoline and 24.4 cents per gallon of diesel fuel and related excise taxes. It currently has two account ...
, established by the Highway Revenue Act in 1956, prescribed a three-cent-per-gallon fuel tax, soon increased to 4.5 cents per gallon. Since 1993 the tax has remained at 18.4 cents per gallon. Other excise taxes related to highway travel also accumulated in the Highway Trust Fund. Initially, that fund was sufficient for the federal portion of building the Interstate system, built in the early years with "10 cent dollars", from the perspective of the states, as the federal government paid 90% of the costs while the state paid 10%. The system grew more rapidly than the rate of the taxes on fuel and other aspects of driving (e. g., excise tax on tires). The rest of the costs of these highways are borne by general fund receipts, bond issues, designated property taxes, and other taxes. The federal contribution comes overwhelmingly from motor vehicle and fuel taxes (93.5 percent in 2007), as does about 60 percent of the state contribution. However, any local government contributions are overwhelmingly from sources besides user fees. As decades passed in the 20th century and into the 21st century, the portion of the user fees spent on highways themselves covers about 57 percent of their costs, with about one-sixth of the user fees being sent to other programs, including the mass transit systems in large cities. Some large sections of Interstate Highways that were planned or constructed before 1956 are still operated as toll roads, for example the
Massachusetts Turnpike The Massachusetts Turnpike (colloquially "Mass Pike" or "the Pike") is a toll highway in the US state of Massachusetts that is maintained by the Massachusetts Department of Transportation (MassDOT). The turnpike begins at the New York state li ...
(I-90), the
New York State Thruway , direction_a = South , terminus_a = {{Jct, state=NY, I, 95 at the The Bronx, Bronx–Yonkers, New York City line , junction = {{plainlist, * {{jct, state=NY, I, 287, Parkway, Saw Mill, NY, 119 in Elmsford, New York, Elmsford * {{jct, state=NY, ...
(I-87 and I-90), and
Kansas Turnpike The Kansas Turnpike is a , freeway-standard toll road that lies entirely within the US state of Kansas. It runs in a general southwest–northeast direction from the Oklahoma border to Kansas City. It passes through several major Kansas cities, ...
(I-35, I-335, I-470, I-70). Others have had their construction bonds paid off and they have become toll-free, such as the Connecticut Turnpike (I‑95), the Richmond-Petersburg Turnpike in Virginia (also I‑95), and the
Kentucky Turnpike Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia t ...
(I‑65). As American suburbs have expanded, the costs incurred in maintaining freeway infrastructure have also grown, leaving little in the way of funds for new Interstate construction. This has led to the proliferation of toll roads (turnpikes) as the new method of building limited-access highways in suburban areas. Some Interstates are privately maintained (for example, the VMS company maintains I‑35 in Texas) to meet rising costs of maintenance and allow state departments of transportation to focus on serving the fastest-growing regions in their states. Parts of the Interstate System might have to be tolled in the future to meet maintenance and expansion demands, as has been done with adding toll HOV/ HOT lanes in cities such as
Atlanta Atlanta ( ) is the capital and most populous city of the U.S. state of Georgia. It is the seat of Fulton County, the most populous county in Georgia, but its territory falls in both Fulton and DeKalb counties. With a population of 498,7 ...
,
Dallas Dallas () is the third largest city in Texas and the largest city in the Dallas–Fort Worth metroplex, the fourth-largest metropolitan area in the United States at 7.5 million people. It is the largest city in and seat of Dallas County ...
, and
Los Angeles Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world ...
. Although part of the tolling is an effect of the SAFETEA‑LU act, which has put an emphasis on toll roads as a means to reduce congestion, present federal law does not allow for a state to change a freeway section to a tolled section for all traffic.


Tolls

About of toll roads are included in the Interstate Highway System. While federal legislation initially banned the collection of tolls on Interstates, many of the toll roads on the system were either completed or under construction when the Interstate Highway System was established. Since these highways provided logical connections to other parts of the system, they were designated as Interstate highways.
Congress A congress is a formal meeting of the representatives of different countries, constituent states, organizations, trade unions, political parties, or other groups. The term originated in Late Middle English to denote an encounter (meeting of ...
also decided that it was too costly to either build toll-free Interstates parallel to these toll roads, or directly repay all the bondholders who financed these facilities and remove the tolls. Thus, these toll roads were
grandfathered A grandfather clause, also known as grandfather policy, grandfathering, or grandfathered in, is a provision in which an old rule continues to apply to some existing situations while a new rule will apply to all future cases. Those exempt from t ...
into the Interstate Highway System. Toll roads designated as Interstates (such as the
Massachusetts Turnpike The Massachusetts Turnpike (colloquially "Mass Pike" or "the Pike") is a toll highway in the US state of Massachusetts that is maintained by the Massachusetts Department of Transportation (MassDOT). The turnpike begins at the New York state li ...
) were typically allowed to continue collecting tolls, but are generally ineligible to receive federal funds for maintenance and improvements. Some toll roads that did receive federal funds to finance emergency repairs (notably the Connecticut Turnpike (I-95) following the
Mianus River Bridge The Mianus River Bridge is a span that carries Interstate 95 ( Connecticut Turnpike) over the Mianus River, between Cos Cob and Riverside, Connecticut. It is the second bridge on the site. The original bridge collapsed in 1983, killing thre ...
collapse) were required to remove tolls as soon as the highway's construction bonds were paid off. In addition, these toll facilities were grandfathered from
Interstate Highway standards Standards for Interstate Highways in the United States are defined by the American Association of State Highway and Transportation Officials (AASHTO) in the publication ''A Policy on Design Standards: Interstate System''. For a certain highway to ...
. A notable example is the western approach to the
Benjamin Franklin Bridge The Benjamin Franklin Bridge, originally named the Delaware River Bridge and known locally as the Ben Franklin Bridge, is a suspension bridge across the Delaware River connecting Philadelphia, Pennsylvania, and Camden, New Jersey. Owned and ...
in
Philadelphia Philadelphia, often called Philly, is the largest city in the Commonwealth of Pennsylvania, the sixth-largest city in the U.S., the second-largest city in both the Northeast megalopolis and Mid-Atlantic regions after New York City. Since ...
, where
I-676 Interstate 676 (I-676) is an Interstate Highway that serves as a major thoroughfare through Center City Philadelphia, where it is known as the Vine Street Expressway, and Camden, New Jersey, where it is known as the northern segment of the ...
has a surface street section through a historic area. Policies on toll facilities and Interstate Highways have since changed. The
Federal Highway Administration The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program ...
has allowed some states to collect tolls on existing Interstate Highways, while a recent extension of I-376 included a section of Pennsylvania Route 60 that was tolled by the
Pennsylvania Turnpike Commission The Pennsylvania Turnpike Commission (PTC) is an agency created in 1937 to construct, finance, operate, and maintain the Pennsylvania Turnpike (both the mainline and the Northeast Extension). The commission consists of five members. Four membe ...
before receiving Interstate designation. Also, newer toll facilities (like the tolled section of I-376, which was built in the early 1990s) must conform to Interstate standards. A new addition of the ''
Manual on Uniform Traffic Control Devices The ''Manual on Uniform Traffic Control Devices for Streets and Highways'' (usually referred to as the ''Manual on Uniform Traffic Control Devices'', abbreviated MUTCD) is a document issued by the Federal Highway Administration (FHWA) of the Unit ...
'' in 2009 requires a black-on-yellow "Toll" sign to be placed above the Interstate trailblazer on Interstate Highways that collect tolls. Legislation passed in 2005 known as SAFETEA-LU, encouraged states to construct new Interstate Highways through "innovative financing" methods. SAFETEA-LU facilitated states to pursue innovative financing by easing the restrictions on building interstates as toll roads, either through state agencies or through
public–private partnership A public–private partnership (PPP, 3P, or P3) is a long-term arrangement between a government and private sector institutions.Hodge, G. A and Greve, C. (2007), Public–Private Partnerships: An International Performance Review, Public Adminis ...
s. However, SAFETEA-LU left in place a prohibition of installing tolls on existing toll-free Interstates, and states wishing to toll such routes to finance upgrades and repairs must first seek approval from Congress. Many states have started using
High-occupancy toll lane A high-occupancy toll lane (or HOT lane) is a type of traffic lane or roadway that is available to high-occupancy vehicles and other exempt vehicles without charge; other vehicles are required to pay a variable fee that is adjusted in response ...
and other partial tolling methods, whereby certain lanes of highly congested freeways are tolled, while others are left free, allowing people to pay a fee to travel in less congested lanes. Examples of recent projects to add HOT lanes to existing freeways include the
Virginia HOT lanes Virginia HOT lanes refers to six separate projects in the U.S. state of Virginia. The first project, completed in November 2012, added high-occupancy/toll (HO/T) lanes to the Capital Beltway (I-495) in Fairfax County. The second project, open ...
on the Virginia portions of the
Capital Beltway The Capital Beltway is a Interstate Highway in the Washington metropolitan area that surrounds Washington, D.C., the capital of the United States, and its inner suburbs in adjacent Maryland and Virginia. It is the basis of the phrase " inside ...
and other related interstate highways (I-95, I-495, I-395) and the addition of express toll lanes to
Interstate 77 in North Carolina Interstate 77 (I-77) is a part of the Interstate Highway System that runs from Columbia, South Carolina, to Cleveland, Ohio. In North Carolina, I-77 enters the state at Charlotte, from South Carolina. Crossing the Piedmont, it connects wi ...
in the
Charlotte metropolitan area The Charlotte metropolitan area, sometimes referred to as Metrolina, is a metropolitan area of the U.S. states of North and South Carolina, within and surrounding the city of Charlotte. The metropolitan area also includes the cities of Gasto ...
.


Chargeable and non-chargeable Interstate routes

Interstate Highways financed with federal funds are known as "chargeable" Interstate routes, and are considered part of the network of highways. Federal laws also allow "non-chargeable" Interstate routes, highways funded similarly to state and U.S. Highways to be signed as Interstates, if they both meet the Interstate Highway standards and are logical additions or connections to the system. These additions fall under two categories: routes that already meet Interstate standards, and routes not yet upgraded to Interstate standards. Only routes that meet Interstate standards may be signed as Interstates once their proposed number is approved.


Signage


Interstate shield

Interstate Highways are signed by a number placed on a red, white, and blue
sign A sign is an object, quality, event, or entity whose presence or occurrence indicates the probable presence or occurrence of something else. A natural sign bears a causal relation to its object—for instance, thunder is a sign of storm, or ...
. The shield design itself is a
registered trademark The registered trademark symbol, , is a typographic symbol that provides notice that the preceding word or symbol is a trademark or service mark that has been registered with a national trademark office. A trademark is a symbol, word, or wor ...
of the
American Association of State Highway and Transportation Officials The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test protocols, and guidelines that are used in highway design and construction throughout the United ...
. The colors red, white, and blue were chosen because they are the colors of the
American flag The national flag of the United States of America, often referred to as the ''American flag'' or the ''U.S. flag'', consists of thirteen equal horizontal stripes of red (top and bottom) alternating with white, with a blue rectangle in the ca ...
. In the original design, the name of the state was displayed above the highway number, but in many states, this area is now left blank, allowing for the printing of larger and more-legible digits. Signs with the shield alone are placed periodically throughout each Interstate as reassurance markers. These signs usually measure high, and are wide for two-digit Interstates or for three-digit Interstates. Interstate business loops and spurs use a special shield in which the red and blue are replaced with green, the word "BUSINESS" appears instead of "INTERSTATE", and the word "SPUR" or "LOOP" usually appears above the number. The green shield is employed to mark the main route through a city's central business district, which intersects the associated Interstate at one (spur) or both (loop) ends of the business route. The route usually traverses the main thoroughfare(s) of the city's downtown area or other major business district. A city may have more than one Interstate-derived business route, depending on the number of Interstates passing through a city and the number of significant business districts therein. Over time, the design of the Interstate shield has changed. In 1957 the Interstate shield designed by
Texas Highway Department The Texas Department of Transportation (TxDOT ) is a government agency in the American state of Texas. Though the public face of the agency is generally associated with the construction and maintenance of the state's immense state highway syste ...
employee Richard Oliver was introduced, the winner of a contest that included 100 entries; at the time, the shield color was a dark navy blue and only wide. The ''
Manual on Uniform Traffic Control Devices The ''Manual on Uniform Traffic Control Devices for Streets and Highways'' (usually referred to as the ''Manual on Uniform Traffic Control Devices'', abbreviated MUTCD) is a document issued by the Federal Highway Administration (FHWA) of the Unit ...
'' (MUTCD) standards revised the shield in the 1961, 1971, and 1978 editions.


Exit numbering

The majority of Interstates have
exit number An exit number is a number assigned to a road junction, usually an exit from a freeway. It is usually marked on the same sign as the destinations of the exit. In some countries, such as the United States, it is also marked on a sign in the go ...
s. Like other highways, Interstates feature guide signs that list control cities to help direct drivers through interchanges and exits toward their desired destination. All
traffic sign Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest signs were simple wooden or stone milestones. Later, signs with directional arms were introduce ...
s and
lane In road transport, a lane is part of a roadway that is designated to be used by a single line of vehicles to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in each ...
markings on the Interstates are supposed to be designed in compliance with the
Manual on Uniform Traffic Control Devices The ''Manual on Uniform Traffic Control Devices for Streets and Highways'' (usually referred to as the ''Manual on Uniform Traffic Control Devices'', abbreviated MUTCD) is a document issued by the Federal Highway Administration (FHWA) of the Unit ...
(MUTCD). There are, however, many local and regional variations in signage. For many years, California was the only state that did not use an exit numbering system. It was granted an exemption in the 1950s due to having an already largely completed and signed highway system; placing exit number signage across the state was deemed too expensive. To control costs, California began to incorporate exit numbers on its freeways in 2002—Interstate, U.S., and state routes alike.
Caltrans The California Department of Transportation (Caltrans) is an executive department of the U.S. state of California. The department is part of the cabinet-level California State Transportation Agency (CalSTA). Caltrans is headquartered in Sacrame ...
commonly installs exit number signage only when a freeway or interchange is built, reconstructed, retrofitted, or repaired, and it is usually tacked onto the top-right corner of an already existing sign. Newer signs along the freeways follow this practice as well. Most exits along California's Interstates now have exit number signage, particularly in rural areas. California, however, still does not use mileposts, although a few exist for experiments or for special purposes. In 2010–2011, the Illinois State Toll Highway Authority posted all new mile markers to be uniform with the rest of the state on I‑90 (Jane Addams Memorial/Northwest Tollway) and the I‑94 section of the Tri‑State Tollway, which previously had matched the I‑294 section starting in the south at I‑80/I‑94/IL Route 394. This also applied to the tolled portion of the Ronald Reagan Tollway (I-88). The tollway also added exit number tabs to the exits. Exit numbers correspond to Interstate mileage markers in most states. On I‑19 in
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
, however, length is measured in kilometers instead of miles because, at the time of construction, a push for the United States to change to a
metric system The metric system is a system of measurement that succeeded the decimalised system based on the metre that had been introduced in France in the 1790s. The historical development of these systems culminated in the definition of the Intern ...
of measurement had gained enough traction that it was mistakenly assumed that all highway measurements would eventually be changed to metric; proximity to metric-using Mexico may also have been a factor, as I‑19 indirectly connects I‑10 to the
Mexican Federal Highway Federal Highways ( es, Carretera Federal), are a series of highways that connect with roads from foreign countries; link two or more states of the Federation; and are wholly or mostly built by the Federation with federal funds or through federal ...
system via surface streets in Nogales. Mileage count increases from west to east on most even-numbered Interstates; on odd-numbered Interstates mileage count increases from south to north. Some highways, including the
New York State Thruway , direction_a = South , terminus_a = {{Jct, state=NY, I, 95 at the The Bronx, Bronx–Yonkers, New York City line , junction = {{plainlist, * {{jct, state=NY, I, 287, Parkway, Saw Mill, NY, 119 in Elmsford, New York, Elmsford * {{jct, state=NY, ...
, use sequential exit-numbering schemes. Exits on the New York State Thruway count up from
Yonkers Yonkers () is a city in Westchester County, New York, United States. Developed along the Hudson River, it is the third most populous city in the state of New York (state), New York, after New York City and Buffalo, New York, Buffalo. The popul ...
traveling north, and then west from Albany. I‑87 in New York State is numbered in three sections. The first section makes up the
Major Deegan Expressway Interstate 87 (I-87) is a north–south Interstate Highway located entirely within the US state of New York. It is most of the main highway between New York City and Montreal. The highway begins at exit 47 off I-278 in the New York ...
in the
Bronx The Bronx () is a borough of New York City, coextensive with Bronx County, in the state of New York. It is south of Westchester County; north and east of the New York City borough of Manhattan, across the Harlem River; and north of the New Y ...
, with interchanges numbered sequentially from 1 to 14. The second section of I‑87 is a part of the
New York State Thruway , direction_a = South , terminus_a = {{Jct, state=NY, I, 95 at the The Bronx, Bronx–Yonkers, New York City line , junction = {{plainlist, * {{jct, state=NY, I, 287, Parkway, Saw Mill, NY, 119 in Elmsford, New York, Elmsford * {{jct, state=NY, ...
that starts in Yonkers (exit 1) and continues north to Albany (exit 24); at Albany, the Thruway turns west and becomes I‑90 for exits 25 to 61. From Albany north to the Canadian border, the exits on I‑87 are numbered sequentially from 1 to 44 along the
Adirondack Northway Interstate 87 (I-87) is a north–south Interstate Highway located entirely within the US state of New York. It is most of the main highway between New York City and Montreal. The highway begins at exit 47 off I-278 in the New York ...
. This often leads to confusion as there is more than one exit on I‑87 with the same number. For example, exit 4 on Thruway section of I‑87 connects with the Cross County Parkway in Yonkers, but exit 4 on the Northway is the exit for the Albany airport. These two exits share a number but are located apart. Many northeastern states label exit numbers sequentially, regardless of how many miles have passed between exits. States in which Interstate exits are still numbered sequentially are Connecticut, Delaware, New Hampshire, New York, Rhode Island, and Vermont; as such, three of the main Interstate Highways that remain completely within these states ( 87, 88, 89) have interchanges numbered sequentially along their entire routes. Maine, Massachusetts, Pennsylvania, Virginia, Georgia, and Florida followed this system for a number of years, but have since converted to mileage-based exit numbers. Georgia renumbered in 2000, while Maine did so in 2004—Massachusetts was the most recent state to convert their exit numbers, finishing in 2021. The
Pennsylvania Turnpike The Pennsylvania Turnpike (Penna Turnpike or PA Turnpike) is a toll highway operated by the Pennsylvania Turnpike Commission (PTC) in the U.S. state of Pennsylvania. A controlled-access highway, it runs for across the state. The turnpike's we ...
uses both mile marker numbers and sequential numbers. Mile marker numbers are used for signage, while sequential numbers are used for numbering interchanges internally. The
New Jersey Turnpike The New Jersey Turnpike (NJTP) is a system of controlled-access highways in the U.S. state of New Jersey. The turnpike is maintained by the New Jersey Turnpike Authority (NJTA).The Garden State Parkway, although maintained by NJTA, is not cons ...
, including the portions that are signed as I‑95 and I‑78, also has sequential numbering, but other Interstates within New Jersey use mile markers.


Sign locations

There are four common signage methods on Interstates: * Locating a sign on the ground to the side of the highway, mostly the right, and is used to denote exits, as well as
rest area A rest area is a public facility located next to a large thoroughfare such as a motorway, expressway, or highway, at which drivers and passengers can rest, eat, or refuel without exiting onto secondary roads. Other names include motorway serv ...
s, motorist services such as gas and lodging, recreational sites, and freeway names * Attaching the sign to an overpass * Mounting on full gantries that bridge the entire width of the highway and often show two or more signs * Mounting on half-gantries that are located on one side of the highway, like a ground-mounted sign


Statistics


Volume

* Heaviest traveled: 379,000 vehicles per day: I-405 in Los Angeles, California (2011 estimate).


Elevation

* Highest: :
I-70 Interstate 70 (I-70) is a major east–west Interstate Highway in the United States that runs from I-15 near Cove Fort, Utah, to a park and ride lot just east of I-695 in Baltimore, Maryland, and is the fifth-longest Interstate in the c ...
in the Eisenhower Tunnel at the
Continental Divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not c ...
in the
Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the ...
Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico ...
. * Lowest (land): : I-8 at the New River near
Seeley, California Seeley is a census-designated place (CDP) in Imperial County, California. Seeley is located west of El Centro. The population was 1,823 at the 2010 census, up from 1,624 in 2000. It is part of the El Centro Metropolitan Area. History The firs ...
. * Lowest (underwater): :
I-95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from US Route 1 (US 1) in Miami, Florida, to the Houlton–Woodstock Border Crossing between Maine and the Canadia ...
in the
Fort McHenry Tunnel The Fort McHenry Tunnel is a four-tube, bi-directional tunnel that carries traffic on Interstate 95 (I-95) underneath the Baltimore Harbor. The lowest point in the Interstate System under water, the tunnel is named for nearby Fort McHenry. T ...
under the
Baltimore Inner Harbor The Inner Harbor is a historic seaport, tourist attraction, and landmark of the city of Baltimore, Maryland. It was described by the Urban Land Institute in 2009 as "the model for post-industrial waterfront redevelopment around the world". The ...
.


Length

* Longest (east–west): :
I-90 Interstate 90 (I-90) is an east–west transcontinental freeway and the longest Interstate Highway in the United States at . It begins in Seattle, Washington, and travels through the Pacific Northwest, Mountain West, Great Plains, Midwest, an ...
from Boston, Massachusetts, to
Seattle, Washington Seattle ( ) is a seaport city on the West Coast of the United States. It is the seat of King County, Washington. With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest region ...
. * Longest (north–south): :
I-95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from US Route 1 (US 1) in Miami, Florida, to the Houlton–Woodstock Border Crossing between Maine and the Canadia ...
from the
Canadian border Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...
near
Houlton, Maine Houlton is a town in Aroostook County, Maine, on the Canada–United States border. As of the 2020 census, the town's population was 6,055. It is perhaps best known for being at the northern terminus of Interstate 95 and as the birthplace of S ...
, to
Miami, Florida Miami ( ), officially the City of Miami, known as "the 305", "The Magic City", and "Gateway to the Americas", is a coastal metropolis and the county seat of Miami-Dade County in South Florida, United States. With a population of 442,241 at ...
. * Shortest (two-digit): :
I-69W Interstate 69W (I-69W) is a relatively short north–south Interstate Highway running through South Texas in the United States. The freeway begins northeast of the middle of World Trade International Bridge in Laredo and ends at I-35. In ...
in
Laredo, Texas Laredo ( ; ) is a city in and the county seat of Webb County, Texas, United States, on the north bank of the Rio Grande in South Texas, across from Nuevo Laredo, Tamaulipas, Mexico. Laredo has the distinction of flying seven flags (the Flag of th ...
. * Shortest (auxiliary): : I-878 in
Queens Queens is a borough of New York City, coextensive with Queens County, in the U.S. state of New York. Located on Long Island, it is the largest New York City borough by area. It is bordered by the borough of Brooklyn at the western tip of Long ...
,
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
,
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
. * Longest segment between state lines: : I-10 in Texas from the
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...
state line near El Paso to the
Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is bord ...
state line near
Orange, Texas Orange is a city and the county seat of Orange County, Texas, United States. As of the 2020 census, the city population was 19,324. It is the easternmost city in Texas, located on the Sabine River at the border with Louisiana, and is from Hous ...
. * Shortest segment between state lines: :
Interstate 95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from US Route 1 (US 1) in Miami, Florida, to the Houlton–Woodstock Border Crossing between Maine and the Canadia ...
/ I-495 (Capital Beltway) on the
Woodrow Wilson Bridge The Woodrow Wilson Memorial Bridge (also known as the Woodrow Wilson Bridge or the Wilson Bridge) is a bascule bridge that spans the Potomac River between the independent city of Alexandria, Virginia, and Oxon Hill in Prince George's County, ...
across the
Potomac River The Potomac River () drains the Mid-Atlantic United States, flowing from the Potomac Highlands into Chesapeake Bay. It is long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map. Retrieved Augu ...
where they briefly cross the southernmost tip of the
District of Columbia ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle (Washington, D.C.), Logan Circle, Jefferson Memoria ...
between its borders with
Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean t ...
and
Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth are ...
. * Longest concurrency: :
I-80 Interstate 80 (I-80) is an east–west transcontinental freeway that crosses the United States from downtown San Francisco, California, to Teaneck, New Jersey, in the New York metropolitan area. The highway was designated in 1956 as one o ...
and
I-90 Interstate 90 (I-90) is an east–west transcontinental freeway and the longest Interstate Highway in the United States at . It begins in Seattle, Washington, and travels through the Pacific Northwest, Mountain West, Great Plains, Midwest, an ...
;
Gary, Indiana Gary is a city in Lake County, Indiana, United States. The city has been historically dominated by major industrial activity and is home to U.S. Steel's Gary Works, the largest steel mill complex in North America. Gary is located along th ...
, to
Elyria, Ohio Elyria ( ) is a city in the Greater Cleveland metropolitan statistical area and the county seat of Lorain County, Ohio, United States, located at the forks of the Black River in Northeast Ohio 23 miles southwest of Cleveland. As of the 2020 ...
.


States

* Most states served by an Interstate: 15 states plus the District of Columbia:
I-95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from US Route 1 (US 1) in Miami, Florida, to the Houlton–Woodstock Border Crossing between Maine and the Canadia ...
through
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
,
Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to the ...
,
South Carolina )''Animis opibusque parati'' ( for, , Latin, Prepared in mind and resources, links=no) , anthem = " Carolina";" South Carolina On My Mind" , Former = Province of South Carolina , seat = Columbia , LargestCity = Charleston , LargestMetro = ...
,
North Carolina North Carolina () is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. The state is the List of U.S. states and territories by area, 28th largest and List of states and territories of the United ...
,
Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth are ...
, DC,
Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean t ...
,
Delaware Delaware ( ) is a state in the Mid-Atlantic region of the United States, bordering Maryland to its south and west; Pennsylvania to its north; and New Jersey and the Atlantic Ocean to its east. The state takes its name from the adjacent ...
,
Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
,
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delawa ...
,
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
,
Connecticut Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York (state), New York to the west, and Long Island Sound to the ...
,
Rhode Island Rhode Island (, like ''road'') is a U.S. state, state in the New England region of the Northeastern United States. It is the List of U.S. states by area, smallest U.S. state by area and the List of states and territories of the United States ...
,
Massachusetts Massachusetts (Massachusett: ''Muhsachuweesut Massachusett_writing_systems.html" ;"title="nowiki/> məhswatʃəwiːsət.html" ;"title="Massachusett writing systems">məhswatʃəwiːsət">Massachusett writing systems">məhswatʃəwiːsət'' En ...
,
New Hampshire New Hampshire is a U.S. state, state in the New England region of the northeastern United States. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Gulf of Maine to the east, and the Canadian province of Quebec t ...
, and
Maine Maine () is a state in the New England and Northeastern regions of the United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Canadian provinces of New Brunswick and Quebec to the northeast and nor ...
. * Most Interstates in a state: 32 routes: New York, totaling * Most primary Interstates in a state: 13 routes: Illinois * Most Interstate mileage in a state: : Texas, in 17 different routes. * Fewest Interstates in a state: 3 routes: Delaware, New Mexico, North Dakota, Puerto Rico, and Rhode Island * Fewest primary Interstates in a state: 1 route: Delaware, Maine, and Rhode Island (I-95 in each case). * Least Interstate mileage in a state: : Delaware, in 3 different routes.


Impact and reception

Following the passage of the Federal Aid Highway Act of 1956, the railroad system for passengers and freight declined sharply, but the trucking industry expanded dramatically and the cost of shipping and travel fell sharply.
Suburbanization Suburbanization is a population shift from central urban areas into suburbs, resulting in the formation of (sub)urban sprawl. As a consequence of the movement of households and businesses out of the city centers, low-density, peripheral urba ...
became possible, with the rapid growth of larger, sprawling, and more car dependent housing than was available in central cities. Tourism dramatically expanded as well, creating a demand for more service stations, motels, restaurants and visitor attractions. There was much more long-distance movement to the
Sun Belt The Sun Belt is a region of the United States generally considered to stretch across the Southeast and Southwest. Another rough definition of the region is the area south of the 36th parallel. Several climates can be found in the region — d ...
for winter vacations, or for permanent relocation, with convenient access to visits to relatives back home. In rural areas, towns and small cities off the grid lost out as shoppers followed the interstate and new factories were located near them. The system had a profound effect on interstate shipping. The Interstate Highway System was being constructed at the same time as the
intermodal shipping container An intermodal container, often called a shipping container, is a large standardized shipping container, designed and built for intermodal freight transport, meaning these containers can be used across different modes of transport – from shi ...
made its debut. These containers could be placed on trailers behind trucks and shipped across the country with ease. A new road network and shipping containers that could be easily moved from ship to train to truck, meant that overseas manufacturers and domestic startups could get their products to market quicker than ever, allowing for accelerated economic growth. Forty years after its construction, the Interstate Highway system returned on investment, making $6 for every $1 spent on the project. The system had a particularly strong effect in Southern states, where major highways were inadequate. The new system facilitated the relocation of heavy manufacturing to the South and spurred the development of Southern-based corporations like
Walmart Walmart Inc. (; formerly Wal-Mart Stores, Inc.) is an American multinational retail corporation that operates a chain of hypermarkets (also called supercenters), discount department stores, and grocery stores from the United States, headquarter ...
(in Arkansas) and
FedEx FedEx Corporation, formerly Federal Express Corporation and later FDX Corporation, is an American multinational conglomerate holding company focused on transportation, e-commerce and business services based in Memphis, Tennessee. The name "Fe ...
(in Tennessee). The Interstate Highway System also dramatically affected American culture. Cars have always been a large part of American culture. Driving was considered an excursion that required some amount skill and could have some chance of unpredictability. With the standardization of signs, road widths and rules, these unpredictabilities became a thing of the past. Justin Fox wrote, "By making road more reliable and by making Americans more reliant on them, they took away most of the adventure and romance associated with driving." The Interstate Highway System has been criticized for contributing to the decline of some cities that were too far from it and for displacing minority neighborhoods in urban centers. Highways have also been criticized for increasing racial segregation by creating physical barriers between neighborhoods. One example of this is the journal article, "What Did Interstate Highways Do to Urban Neighborhoods?”. This journal article brings up the notion that the authors believe that the construction of urban highways led to the destruction of racially diverse neighborhoods. However, they also acknowledge that other contributing factors led to this well. Other critics have blamed the Interstate Highway System for the decline of
public transportation in the United States In public relations and communication science, publics are groups of individual people, and the public (a.k.a. the general public) is the totality of such groupings. This is a different concept to the sociological concept of the ''Öffentlichkei ...
since the 1950s.


See also

*
Highway systems by country This article describes the highway systems available in selected countries. Albania In Albania, major cities are linked with either new single/dual carriageways or well maintained state roads marked as "SH" (). There is a dual carriageway conn ...
* List of controlled-access highway systems *
Non-motorized access on freeways Non-motorized access on freeways may allow or restrict pedestrians, bicyclists and other non-motorized traffic to use a freeway. Such roads are public ways intended primarily for high-speed travel over long distances, and they have resulted in hig ...


Notes


References


Further reading

* * * * * * *


External links

*
Dwight D. Eisenhower National System of Interstate and Defense Highways
Federal Highway Administration (FHWA)
Route Log and Finder List
FHWA
Turner-Fairbank Highway Research Center
FHWA
Interstate Highway System
Dwight D. Eisenhower Presidential Library and Museum

''NOW'' on PBS {{Authority control 1956 establishments in the United States Presidency of Dwight D. Eisenhower Transport systems Types of roads