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Interstate 19 (I-19) is a north–south
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. Th ...
located entirely within the US state of
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 Fo ...
. I-19 travels from Nogales, roughly from the
Mexican border Mexico shares international borders with three nations: *To the north the United States–Mexico border, which extends for a length of through the states of Baja California, Sonora, Chihuahua, Coahuila, Nuevo León and Tamaulipas. *To the sout ...
, to
Tucson , "(at the) base of the black ill , nicknames = "The Old Pueblo", "Optics Valley", "America's biggest small town" , image_map = , mapsize = 260px , map_caption = Interactive map ...
, at
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 ...
. The highway also travels through the cities of Rio Rico, Green Valley, and Sahuarita. Having a total length of just over , I-19 is the seventh-shortest primary (two-digit) Interstate Highway in the contiguous 48 states, where only I-87 (North Carolina), I-97,
I-86 Interstate 86 may refer to any of three unconnected Interstate Highways in the United States: * Interstate 86 (Pennsylvania–New York) Interstate 86 (I-86) is an Interstate Highway that extends for through northwestern Pennsylvania a ...
(Idaho), I-14, I-11, and I-2 are shorter. While the highway is short, it is a very important corridor, serving as a fast route from Tucson and Phoenix (via I-10) to the Mexican border. The highway is a portion of the United States section 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 ...
, a trade corridor that stretches north from
Mexico Mexico ( Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Gua ...
across the United States to the Canadian 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 Terr ...
.


Route description

In Nogales, the southern terminus of I-19 is at West Crawford Street, adjacent to the international port of entry, and southbound travelers can continue into Nogales, Sonora, Mexico, via state-maintained surface roads, and connect with Mexican Federal Highway 15 (Fed. 15) either to the south or west of Nogales, Sonora. Starting from the southern terminus at kilometer post 0 ( not milepost 0), I-19 initially heads briefly south then west on surface streets, navigating its way through the town of Nogales for before becoming an Interstate–grade freeway and making the turn to head north toward Tucson. It has interchanges with two other state highways near the southern end of the route, State Route 189 (SR 189) at exit 4 and SR 289 at exit 12. The interchange with SR 189 at exit 4 both serves to funnel traffic so as to bypass around Nogales, Arizona, and Nogales, Sonora, for travelers bound to or from
Hermosillo Hermosillo (), formerly called Pitic (as in ''Santísima Trinidad del Pitic'' and ''Presidio del Pitic''), is a city located in the center of the northwestern Mexican state of Sonora. It is the municipal seat of the Hermosillo municipality, the ...
or
Mexico City Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley ...
, and provides for the continuous flow of freight and truck traffic through the larger Mariposa Port of Entry to Fed. 15, which has its northern terminus at the US–Mexico border with SR 189 and its southern terminus away in
Mexico City Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley ...
. After exiting Nogales to the north, I-19 passes near and around a series of sparsely-populated towns and retirement communities along the banks of the Santa Cruz River, including Rio Rico, Tubac, Amado, Green Valley, and Sahuarita. For several miles near Amado and Green Valley, the eastward view from I-19 provides scenic views of Madera Canyon and the
Santa Rita Mountains The Santa Rita Mountains (O'odham: To:wa Kuswo Doʼag), located about 65 km (40 mi) southeast of Tucson, Arizona, extend 42 km (26 mi) from north to south, then trending southeast. They merge again southeastwards into the Pat ...
in the
Coronado National Forest The Coronado National Forest is a United States National Forest that includes an area of about 1.78 million acres (7,200 km2) spread throughout mountain ranges in southeastern Arizona and southwestern New Mexico. It is located in parts of C ...
. Just before entering
Tucson , "(at the) base of the black ill , nicknames = "The Old Pueblo", "Optics Valley", "America's biggest small town" , image_map = , mapsize = 260px , map_caption = Interactive map ...
, I-19 passes through the eastern section of the
San Xavier Indian Reservation The San Xavier Indian Reservation ( O’odham: Wa:k) is an Indian reservation of the Tohono O’odham Nation located near Tucson, Arizona, in the Sonoran Desert. The San Xavier Reservation lies in the southwestern part of the Tucson metropolitan ...
where it makes its only crossing of the Santa Cruz River. As I-19 enters the Tucson city limits, it has an interchange with SR 86 at exit 99 before reaching its northern terminus at an interchange with I-10. Nearly the entire route of I-19 follows, or is adjacent to, the former routing of U.S. Route 89 (US 89) and the Santa Cruz River, which flows northward from Mexico, through Tucson and usually disperses into the desert between Marana and the
Gila River The Gila River (; O'odham ima Keli Akimel or simply Akimel, Quechan: Haa Siʼil, Maricopa language: Xiil) is a tributary of the Colorado River flowing through New Mexico and Arizona in the United States. The river drains an arid watershed of n ...
, southeast of
Phoenix Phoenix most often refers to: * Phoenix (mythology), a legendary bird from ancient Greek folklore * Phoenix, Arizona, a city in the United States Phoenix may also refer to: Mythology Greek mythological figures * Phoenix (son of Amyntor), a ...
. Most of the time, much of the river is dry, but heavy storms can cause it to overflow its banks, flooding farmland before reaching the Gila River.


Signage

I-19 is unique among US Interstates, because signed distances are given in meters (hundreds or thousands as distance-to-exit indications) or kilometers (as distance-to-destination indications), and not miles. However, the speed limit signs give speeds in miles per hour. According to the
Arizona Department of Transportation The Arizona Department of Transportation (ADOT, pronounced "A-Dot") is an Arizona state government agency charged with facilitating mobility within the state. In addition to managing the state's highway system, the agency is also involved with p ...
(ADOT), metric signs were originally placed because of the push toward the metric system in the United States at the time of the original construction of the highway. I-19 had originally been signed as it was constructed, in a series of small signing contracts that used customary units. In 1980, ADOT awarded a single contract to install new signs which used metric units, to overlay English-unit expressions on some existing signs with metric-unit expressions, to install kilometer posts, and to provide bilingual signing in select locations. The signing scheme used in 1980 provided explicit units on advance guide signs, but not on interchange sequence signs or post-interchange confirmation (distance) signs. The expressions on advance guide signs were of the form "2 km" for distances over and "500 m" for distances under , with no provision for fractional kilometrages. On advance guide signs, the metric unit expressions "km" and "m" were placed on the baseline where "MILES" would otherwise have gone but were sized so that their lowercase loop height matched the uppercase letter height of "MILES" on customary-unit signs. The exception was a handful of advance guide signs for the SR 86 (Ajo Way) exit, which used "KM" (in uppercase, contrary to SI nomenclature) on the same baseline and at the same letter height as "MILES". The 1980 signing plans also provided design details for speed limit and advisory speed signs using metric units, with the limit values enclosed in a red circle on the speed limit sign and a black circle on the yellow-background advisory signs. These speed signs all had explicit units, with "km/h" below the circle enclosing the limit value. However, the advisory signs were canceled by change order and not installed. Had the metric speed limit sign been installed, the signed speed limit on I-19 would have been , which is a close soft-conversion of the then-existing national maximum speed limit. As Arizona's current maximum speed limit is , the metric equivalent would most likely read . Information signs, to three distinct designs, were also placed at various locations on or near I-19 to advise motorists that the highway was signed in metric. Notwithstanding the metric legends, the signing plans were dimensioned entirely in feet and inches. In 1999, ADOT awarded two contracts (administered as a single construction project) to renew the signs along the full length of I-19. The general approach toward metric signing differed from that taken in 1980. Explicit units were given not just on advance guide signs, but also on interchange sequence signs, post-interchange confirmation signs, and community interchange signs (the last-listed had not been used in 1980). On the distance signs, "km" appeared after each kilometer measurement except when one or more of the distances was a fractional kilometer. In such cases, all the distances were given in meters with "meters" (written out in full, not "m") after each distance value. On distance signs in general, "km" or "meters" appeared on the same baseline and with the same letter height as the distance values, while advance guide signs were formatted as in 1980. Since a typical ADOT freeway guide sign rehabilitation contract also replaces surface road signing near those roads' interchanges with the freeway, metric-unit signs also appeared on local roads near I-19, giving distances in kilometers to tourist attractions such as
Mission San Xavier del Bac Mission San Xavier del Bac ( es, La Misión de San Xavier del Bac) is a historic Spanish Catholic mission located about south of downtown Tucson, Arizona, on the Tohono O'odham Nation San Xavier Indian Reservation. The mission was founded in 1 ...
. As was the case in 1980, the signing plans were dimensioned in feet and inches. However, a number of signs near the Valencia Road interchange were replaced or amended when it was converted from a
partial cloverleaf A partial cloverleaf interchange or parclo is a modification of a cloverleaf interchange. The design has been well received, and has since become one of the most popular freeway-to-arterial interchange designs in North America. It has also bee ...
to a
single-point urban interchange A single-point urban interchange (SPUI, or ), also called a single-point interchange (SPI) or single-point diamond interchange (SPDI), is a type of highway interchange. The design was created in order to help move large volumes of traffic thr ...
in 2000. One of these signs has a fractional kilometrage greater than , rendered as "1500 m", while others use "m" rather than "meters" as the unit expression. Metric unit expressions on the advance guide signs installed or modified as part of this contract appear on the same baseline as the metric values, rather than on a raised baseline as on other I-19 advance guide signs. Again, the plans were dimensioned in feet and inches. Citing motorist confusion arising from the metric signs on I-19, ADOT's Tucson district announced that new signs on I-19 would use
United States customary units United States customary units form a system of measurement units commonly used in the United States and U.S. territories since being standardized and adopted in 1832. The United States customary system (USCS or USC) developed from English unit ...
. To avoid the cost of replacing the metric signs all at once, signs would be replaced in specific areas of the freeway during construction projects in those areas. New signs were put into place between exit 99 (Ajo Way) and exit 101 (I-10) in 2004 after the completion of the new I-10/I-19 interchange. As of 2010, the remainder of the project has been stalled due to local opposition, particularly from businesses that would have to change their directions. A reconstruction project at the Interstate's northern terminus with I-10 in Tucson (at the interchange commonly called the Crossing) began in 2002 and completed in August 2004.


History

The first sections of I-19 to be opened to traffic were a stub, from I-10 to Valencia Road, in 1962 and a stretch in Green Valley in 1963. The freeway between Rio Rico and
Nogales, Arizona Nogales (English: or , ; ) is a city in Santa Cruz County, Arizona. The population was 20,837 at the 2010 census and estimated 20,103 in 2019. Nogales forms part of the larger Tucson–Nogales combined statistical area, with a total populatio ...
, was completed in 1974. The major section between Green Valley and Rio Rico was finished in 1978. The official completion date of the I-19 segment between Tucson (km 100) and Green Valley (actually Helmet Peak Road at km 75) was February 12, 1972. A 1978 project report for ADOT lists entire I-19 project as "completed", which includes segments between Green Valley and Nogales.


Future

I-19 is a very heavily traveled corridor in the Tucson metro area. The freeway is currently two lanes in both directions for its entire length, with the exception of the interchange with I-10, where it is four lanes. Current plans call for widening from Irvington Road to Ajo Way, bringing the freeway to three lanes in each direction. Future plans include expansion to up to five lanes in each direction by 2030 from the crossing with I-10 to San Xavier Road. I-19 is also part of the proposed I-11 corridor.


Exit list


Business routes

Historically, I-19 has had two business loops, both of which are former sections of US 89, SR 93, and SR 789. One is currently active while the other is decommissioned. Both business loops are currently and formerly recognized under the unsigned designation Arizona State Route 19 Business (also known as State Business Route 19).


Nogales loop

State Business Route 19 (1) (also known as SR 19 Bus.) begins at the Mexican border in Nogales near the southern end of the Interstate. I-19 Business (I-19 Bus.) follows Grand Avenue in Nogales and has intersections with SR 82 and SR 189 before terminating at I-19 just north of Nogales. The route follows the former alignment of US 89, SR 93, and SR 789, back when all three highways traversed through southern Arizona. The route has been commissioned as I-19 Bus. since US 89 was decommissioned from southern Arizona in 1992. Major intersections


Sahuarita to Tucson loop

State Business Route 19 (2) (also known as SR 19 Bus.) began at I-19 exit 69 in Green Valley at West Duval Mine Road and South Nogales Highway. I-19 Bus. followed Nogales Highway north through unincorporated Pima County and Sahuarita into
Tucson , "(at the) base of the black ill , nicknames = "The Old Pueblo", "Optics Valley", "America's biggest small town" , image_map = , mapsize = 260px , map_caption = Interactive map ...
. In Tucson, I-19 Bus. curved from Nogales Highway onto South 6th Avenue where it served as the eastern terminus of SR 86 at West Ajo Way, before terminating at
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 ...
exit 261 and South 6th Avenue in South Tucson. The route follows the former alignment of US 89, SR 93, and SR 789, back when all three highways traversed through southern Arizona. The route was commissioned as I-19 Bus. since US 89 was decommissioned from southern Arizona in 1992. In 2002, the state handed maintenance of I-19 Bus. between Los Reales Road and I-10 to the city of Tucson. The rest of the route was handed over to Pima County and the city of Sahuarita in 2004. This also meant the designation was retired from the state highway system completely. Major intersections


See also

* List of Interstate Highways in Arizona *
Metrication in the United States Metrication (or metrification) is the process of introducing the International System of Units, also known as SI units or the metric system, to replace a jurisdiction's traditional measuring units. U.S. customary units have been defined in ter ...


References


External links


I-19
at Arizona Roads

at AARoad's Interstate Guide {{DEFAULTSORT:I19 19 19 Transportation in Tucson, Arizona Transportation in Pima County, Arizona Transportation in Santa Cruz County, Arizona Metrication in the United States