Interstate 15 (I-15) is a major

Interstate Highway The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, is a network of controlled-access highways that forms part of the National Highway System in the United States. T ...

in the western

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

, running through

Southern California Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban ...

and the Intermountain West. I-15 begins near the Mexican border in

San Diego County San Diego County (), officially the County of San Diego, is a county in the southwestern corner of the U.S. state of California. As of the 2020 census, the population was 3,298,634, making it California's second-most populous county and the f ...

and stretches north to Alberta, Canada, passing through the states of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...

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 ...

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

Idaho Idaho ( ) is a U.S. state, state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Monta ...

, and

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

. The Interstate serves the cities of

San Diego San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United States ...

, San Bernardino,

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 ...

, St. George, Provo,

Salt Lake City 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, th ...

, Ogden, Pocatello, Idaho Falls,

Butte __NOTOC__ In geomorphology, a butte () is an isolated hill with steep, often vertical sides and a small, relatively flat top; buttes are smaller landforms than mesas, plateaus, and tablelands. The word ''butte'' comes from a French word me ...

Helena Helena may refer to: People *Helena (given name), a given name (including a list of people and characters with the name) *Katri Helena (born 1945), Finnish singer *Helena, mother of Constantine I Places Greece * Helena (island) Guyana * H ...

, and Great Falls. It also passes close to the urban areas of

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 ...

, Orange, and Riverside counties, California. The stretches of I-15 in Idaho, Utah, and Arizona have been designated as the "Veterans Memorial Highway". The southern end is at a junction with I-8 and State Route 15 (SR 15) in

, and the northern end is at a connection with Alberta Highway 4 at the

Sweetgrass–Coutts Border Crossing The Sweetgrass–Coutts Border Crossing connects the town of Sweet Grass, Montana with the village of Coutts, Alberta, on the Canada–United States border. I-15 on the American side joins Alberta Highway 4 on the Canadian side. Similarly, BNS ...

. I-15 was built to connect the

Inland Empire The Inland Empire (IE) is a metropolitan area and region inland of and adjacent to coastal Southern California, centering around the cities of San Bernardino and Riverside, and bordering Los Angeles County to the west. It includes the citie ...

with San Diego in California, facilitate tourism access to Las Vegas, provide access to the Arizona Strip, interconnect all of the

metropolitan statistical area In the United States, a metropolitan statistical area (MSA) is a geographical region with a relatively high population density at its core and close economic ties throughout the area. Such regions are neither legally incorporated as a city or tow ...

s in Utah except for

Logan Logan may refer to: Places * Mount Logan (disambiguation) Australia * Logan (Queensland electoral district), an electoral district in the Queensland Legislative Assembly * Logan, Victoria, small locality near St. Arnaud * Logan City, local gov ...

, and provide freeway bypasses for Pocatello, Idaho Falls, and Great Falls. Since its creation, I-15 has served as a long-haul route for

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

n commerce. It is now officially chartered for this purpose: from the junction of I-515 in

to the Canadian border, I-15 forms part of the CANAMEX Corridor, a High Priority Corridor, as a result of 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 ...

. Since the construction of I-15, California, Idaho, Nevada, and Utah have consistently ranked in the fastest-growing areas of the United States. As a result, the route of I-15 has substantially increased in population and commuter traffic.

Route description

, - , CA , , - , NV , , - , AZ , , - , UT , , - , ID , , - , MT , , - , Total , This highway's southern terminus is in

San Diego, California San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United Stat ...

, at I-8, although via SR 15, a southern extension of the freeway, the route connects to I-5 just north of the Mexico–US border. The northern terminus is in

Sweet Grass, Montana Sweet Grass (also Sweetgrass) is a census-designated place and unincorporated community in Toole County, Montana, United States, on the Canada–US border. It is the northern terminus of Interstate 15, an important route connecting western Ca ...

, at the Canada–US border, where it becomes Alberta Highway 4. It is long from San Diego to Sweet Grass.

California

North of its junction with SR 91 in Corona, the route roughly follows the former routes of State Route 31. North of

Devore Devore may refer to: *Devoré, a fabric technique *Devore, San Bernardino, California * Devore, Indiana People with the surname *Chuck DeVore (born 1962), American politician * Daniel Bradford Devore, (1860–1956), American brigadier general *Doro ...

, the highway follows the approximate alignment of historic US Route 66 along with US 91 and US 395. US 395 breaks away at Hesperia and the route continues on a direct path to Barstow to the north. Meanwhile, the old alignments of US 91 and US 66 follow the Mojave River from Victorville to Barstow along the National Trails Highway. At that point, I-15 follows the old route of US 91 exclusively as US 66 turned east toward Needles. For many parts of the highway, high-voltage powerlines, such as Path 46 and Path 27, almost all originating from the

Hoover Dam Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on S ...

, follow the freeway. Many of these link distant power stations to the

metropolitan area. The southern starting point of I-15 was in 1957 planned to be in San Bernardino, at the interchange with the San Bernardino Freeway (then US 70/US 99, now

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 ...

). This was logical as I-15 was following the old alignment of the historic Route 66 which passed through San Bernardino. The segment was completed accordingly. In 1964, legislation was later passed to extend the Interstate to

. Instead of extending the existing freeway from the I-10 interchange south, however, the

California Department of Transportation 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 Sacram ...

drew a new segment in Devore that "branched" off of the original alignment and bypassed San Bernardino altogether. This segment's alignment is generally northeast to southwest for about . Then, in

Rancho Cucamonga Rancho Cucamonga was a Mexican land grant in present-day San Bernardino County, California, given in 1839 to the dedicated soldier, smuggler and politician Tiburcio Tapia by Mexican governor Juan Bautista Alvarado. The grant formed parts of p ...

, its directional alignment shifts to north–south where it eventually meets with I-10 (about west of the original interchange in San Bernardino). The segment that had been built from Devore to San Bernardino was retained as an Interstate, but was renumbered as I-215. Note that during the construction of I-15's present alignment, and for some time afterward, I-215 was numbered as I-15E, and its actual mileage would begin at I-10. I-15 runs for a total of in California.

Nevada

I-15 begins in Primm and continues through

along the

Las Vegas Strip The Las Vegas Strip is a stretch of Las Vegas Boulevard South in Clark County, Nevada, that is known for its concentration of resort hotels and casinos. The Strip, as it is known, is about long, and is immediately south of the Las Vegas cit ...

corridor. Then, the Interstate crosses the border with

in Mesquite. The Interstate in

runs entirely in Clark County, for a distance of .

Arizona

I-15 passes through the northwestern corner of

with a total length of . The stretch is separated from the rest of the state and has one major exit, at Beaver Dam/

Littlefield, Arizona Littlefield is an unincorporated community and census-designated place in Mohave County, Arizona, United States, that is located in the Arizona Strip region. As of the 2020 census, its population was 256, down from 308 in 2010. It lies just s ...

. It includes a spectacular section where the road twists between the narrow walls of the Virgin River Gorge.

Utah

I-15 continues through

for . It is the main north–south connection for the state. The highway approximately follows the old alignment of US 91 from St. George to

Brigham City Brigham City is a city in Box Elder County, Utah, United States. The population was 17,899 at the 2010 census. It is the county seat of Box Elder County. It lies on the western slope of the Wellsville Mountains, a branch of the Wasatch Range ...

. The highway passes through the fast-growing Utah's Dixie region in the southwestern part of the state, which includes St. George, Cedar City, and eventually most of the major cities and suburbs along 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 ...

, including Provo, Orem,

Sandy Sandy may refer to: People and fictional characters *Sandy (given name), including a list of people and fictional characters * Sandy (surname), a list of people * Sandy (singer), Brazilian singer and actress Sandy Leah Lima (born 1983) * (Sandy) ...

, Layton, and Ogden. Near Cove Fort, I-70 begins its journey eastward across the country. The Interstate merges with I-80 for about from South Salt Lake to just west of

Downtown Salt Lake City Downtown (also called City Center) is the oldest district in Salt Lake City, Utah. The grid plan, grid from which the entire city is laid out originates at Temple Square, the location of the Salt Lake Temple. Location Downtown Salt Lake City is ...

and also merges with

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 ...

from Ogden to Tremonton. Along nearly its entire length through the state, I-15 winds its way along the western edge of a nearly continuous range of mountains (the Wasatch Range in the northern half of the state). The only exceptions are north of Cove Fort and when it passes between Cedar City and St. George, known as the Black Ridge, a transition zone of drastic change in elevation and climate, an area where the eastern

Great Basin The Great Basin is the largest area of contiguous endorheic watersheds, those with no outlets, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja California. It is noted fo ...

Colorado Plateau The Colorado Plateau, also known as the Colorado Plateau Province, is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. This province covers an area o ...

, and

Mojave Desert The Mojave Desert ( ; mov, Hayikwiir Mat'aar; es, Desierto de Mojave) is a desert in the rain shadow of the Sierra Nevada mountains in the Southwestern United States. It is named for the indigenous Mojave people. It is located primarily ...

converge.

Idaho

I-15 passes through

for . I-15 crosses the

state line in Oneida County. The highway runs through Pocatello,

Blackfoot The Blackfoot Confederacy, ''Niitsitapi'' or ''Siksikaitsitapi'' (ᖹᐟᒧᐧᒣᑯ, meaning "the people" or "Blackfoot language, Blackfoot-speaking real people"), is a historic collective name for linguistically related groups that make up t ...

, and Idaho Falls, intersecting with I-86. The last county in Idaho that I-15 passes through is Clark County. Finally, the Interstate reaches the

state line at Monida Pass.

Montana

I-15 continues onward through of

through the cities of

, and Great Falls, intersecting with

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 ...

, I-115, and I-315. At Sweet Grass, I-15 terminates upon crossing the Canadian border into the province of

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 ...

; however, I-15 signage is present on Alberta Highway 4 southbound from

Lethbridge Lethbridge ( ) is a city in the province of Alberta, Canada. With a population of 101,482 in its 2019 municipal census, Lethbridge became the fourth Alberta city to surpass 100,000 people. The nearby Canadian Rocky Mountains contribute to t ...

to the Canadian border.

History

I-15 was constructed along the route of US 91. Once I-15 was relatively intact, US 91 was decommissioned, except for one part in Northern Utah / Southern Idaho where I-15 instead followed the route of former US 191. I-15 originally had two suffixed routes. In California, I-15 had an eastern branch bypassing San Bernardino, which was designated I-15E. I-15E was renumbered and is now I-215. Present day routing of I-15 in California was originally given "I-15W" as its title while it was under construction (the original asphalt portions from Temescal Canyon to Ontario Avenue were dubbed I-15W on maps until 1974), but was never officially signed as such. In Idaho, I-15 had a western branch near Pocatello that connected I-15 and I-84 (then I-80N). This highway was designated I-15W. It is now the western I-86.

Growth along route

Since the construction of I-15, California, Nevada, and Utah have consistently ranked in the fastest-growing areas of the United States. As a result, the route of I-15 has substantially increased in population and commuter traffic has increased the traffic burden on the freeway. Current population estimates are that more than 75 percent of the population of Utah, 19 percent of the population of California, and more than 70 percent of the population of Nevada live in counties where I-15 is the primary

. Similarly, in California, I-15 is seeing more commuter traffic due to the growth of the

communities of Hesperia, Victorville, and Barstow. In Utah, I-15 has been near-constantly upgraded in the

, and future plans released by the Utah Department of Transportation (UDOT) indicate that this will continue in the north ''and'' the far south of the state as well, due to the extremely rapid growth of Washington County and surrounding areas. In like manner,

in Nevada has seen growth along I-15, and in all of the states that it currently serves, it has recently been or is currently in the process of being upgraded to increase capacity and efficiency. The portions in Arizona, Idaho and Montana have retained their rural, long-haul character. Although Arizona has also grown substantially since the construction of I-15, this

highway A highway is any public or private road or other public way on land. It is used for major roads, but also includes other public roads and public tracks. In some areas of the United States, it is used as an equivalent term to controlled-access ...

serves only the isolated corner of northwestern Arizona. Due to this rapid area growth, the I-15 corridor is the focus of several

mass transit Public transport (also known as public transportation, public transit, mass transit, or simply transit) is a system of transport for passengers by group travel systems available for use by the general public unlike private transport, typical ...

projects. The Las Vegas Monorail, '' FrontRunner''

commuter rail Commuter rail, or suburban rail, is a passenger rail transport service that primarily operates within a metropolitan area, connecting commuters to a central city from adjacent suburbs or commuter towns. Generally commuter rail systems are con ...

system, and TRAX light rail in

are mass transit lines loosely parallel to I-15 that are now in operation. Between Los Angeles and Las Vegas has long been proposed as a

maglev train Maglev (derived from '' magnetic levitation''), is a system of train transportation that uses two sets of electromagnets: one set to repel and push the train up off the track, and another set to move the elevated train ahead, taking advantage ...

route; in 2004 the

California–Nevada Interstate Maglev The California–Nevada Interstate Maglev project was a proposed Maglev train line from Las Vegas, Nevada, to Anaheim, California. One segment would run from Las Vegas to Primm, Nevada, with proposed service to the Las Vegas area's forthcoming ...

project held public meetings on the plan.

Future

The segment signed as SR 15 from I-5 to I-8 in

is planned to be redesignated as part of I-15 once this segment is completely upgraded to

Interstate 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 ...

, namely where the freeway's interchange with SR 94 is concerned. The interchange currently has left-exits and blind merges, and is due to be updated with a long-awaited widening of both SR 15 and SR 94. At that time, SR 15 is planned be resigned as part of I-15. The remaining portion of SR 15 conforms with Interstate standards.

Junction list

;California : 32nd Street and Norman Scott Road in Barrio Logan,

(future interchange) : on the Barrio Logan– Southcrest– Logan Heights, San Diego neighborhood line (future interchange) : on the North Park–

City Heights City Heights is a dense urban community in central San Diego, California, known for its ethnic diversity. The area was previously known as East San Diego. City Heights is located south of Mission Valley and northeast of Balboa Park. City Height ...

, San Diego neighborhood line (future interchange) : on the Mission Valley East– Grantville, San Diego neighborhood line : in

Murrieta Murrieta is a city in southwestern Riverside County, California, United States. The population of Murrieta was 110,949 as of the 2020 census. Murrieta experienced a 133.7% population increase between 2000 and 2010, making Murrieta one of the ...

: in

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 ...

: near San Bernardino : in Hesperia : in Barstow ;Nevada : in

Enterprise Enterprise (or the archaic spelling Enterprize) may refer to: Business and economics Brands and enterprises * Enterprise GP Holdings, an energy holding company * Enterprise plc, a UK civil engineering and maintenance company * Enterprise ...

: in

. I-15/US 93 travels concurrently to northeast of

North Las Vegas North Las Vegas is a suburban city in Clark County, Nevada, United States, in the Las Vegas Valley. As of the 2010 census it had a population of 216,961, with an estimated population of 251,974 in 2019. The city was incorporated on May 1, 19 ...

. ;Arizona : No major intersections ;Utah : south-southwest of Cove Fort : north-northeast of

Holden Holden, formerly known as General Motors-Holden, was an Australian subsidiary company of General Motors. It was an Australian automobile manufacturer, importer, and exporter which sold cars under its own marque in Australia. In its last thr ...

. The highways travel concurrently to Scipio. : in Santaquin. The highways travel concurrently to Spanish Fork. : in Provo : in

Lehi Lehi (; he, לח"י – לוחמי חרות ישראל ''Lohamei Herut Israel – Lehi'', "Fighters for the Freedom of Israel – Lehi"), often known pejoratively as the Stern Gang,"This group was known to its friends as LEHI and to its enemie ...

. The highways travel concurrently to Draper. : in

Murray Murray may refer to: Businesses * Murray (bicycle company), an American manufacturer of low-cost bicycles * Murrays, an Australian bus company * Murray International Trust, a Scottish investment trust * D. & W. Murray Limited, an Australian who ...

: in South Salt Lake. The highways travel concurrently to

. : in Salt Lake City : in North Salt Lake : in North Salt Lake : on the West Bountiful– Bountiful city line. The highways travel concurrently to Farmington. : in Riverdale. The highways travel concurrently to Tremonton. : on the Perry–

city line. ;Idaho : north-northwest of

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 ...

. The highways travel concurrently to Pocatello. : northwest of McCammon. The highways travel concurrently to Pocatello. : in Chubbuck : southwest of

: in Blackfoot. The highways travel concurrently to Idaho Falls. : in Idaho Falls. The highways travel concurrently through Idaho Falls. ;Montana : in

. The highways travel concurrently through Butte. : in Butte : in

. I-15/US 287 travels concurrently to northeast of

Wolf Creek Wolf Creek may refer to: Bodies of water Missouri * Wolf Creek (Beaver Creek tributary) * Wolf Creek (Cane Creek tributary) * Wolf Creek (Cave Creek tributary) * Wolf Creek (Elkhorn Creek tributary) * Wolf Creek (South Grand River tributary) * ...

. : in Great Falls. I-15/US 89 travels concurrently to northeast of Vaughn. : in Shelby : at the Sweetgrass-Coutts Border Crossing in the Canadian border east-northeast of Sweet Grass

Auxiliary routes

Inland Empire, California The Inland Empire (IE) is a metropolitan area and region inland of and adjacent to coastal Southern California, centering around the cities of San Bernardino and Riverside, and bordering Los Angeles County to the west. It includes the cities ...

– I-215 *

Henderson, Nevada Henderson is a city in Clark County, Nevada, United States, about southeast of downtown Las Vegas. It is the second largest city in Nevada, after Las Vegas, with an estimated population of 320,189 in 2019. The city is part of the Las Vegas Val ...

– I-515 *

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 ...

– I-215 *

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 ...

– I-215 *

Butte, Montana Butte ( ) is a consolidated city-county and the county seat of Silver Bow County, Montana, United States. In 1977, the city and county governments consolidated to form the sole entity of Butte-Silver Bow. The city covers , and, according to t ...

– I-115 *

Great Falls, Montana Great Falls is the third most populous city in the U.S. state of Montana and the county seat of Cascade County. The population was 60,442 according to the 2020 census. The city covers an area of and is the principal city of the Great Falls, M ...

– I-315

References

External links

* * https://web.archive.org/web/20030626140609/http://www.dot.ca.gov/dist11/facts/I-15managed.pdf * 2005 Rand McNally ''The Road Atlas 2005''- newest feature- interstate mileage by state ; California
California Highways: SR 15

; Arizona
I-15 Completed December 14, 1973
{{DEFAULTSORT:I15 15 U.S. Route 91

Route description

California

Nevada

Arizona

Utah

Idaho

Montana

History

Growth along route

Future

Junction list

Auxiliary routes

See also

References

External links