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Interstate 19
Interstate 19
Interstate 19
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Interstate 19 marker
Interstate 19
Map
I-19 highlighted in red
Route information
Maintained by ADOT
Length102.08 km[1] (63.43 mi)
Existed1963[2]–present
NHSEntire route
Major junctions
South end BL 19 in Nogales
Major intersections
North end I-10 in Tucson
Location
CountryUnited States
StateArizona
CountiesSanta Cruz, Pima
Highway system
  • Arizona State Highway System
← I-17→ SR 24

Interstate 19 (I-19) is a north–south Interstate Highway located entirely within the US state of Arizona. I-19 travels from Nogales, roughly 90 meters (300 ft) from the Mexican border, to Tucson, at I-10. The highway also travels through the cities of Rio Rico, Green Valley, and Sahuarita.

Having a total length of just over 102 kilometers (63 mi), I-19 is the eighth-shortest primary (two-digit) Interstate Highway in the contiguous 48 states, where only I-86 (Idaho), I-11 (Nevada), I-2 (Texas), I-42 (North Carolina), I-14 (Texas), I-97 (Maryland), and I-87 (North Carolina) 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 US section of the CANAMEX Corridor, a trade corridor that stretches north from Mexico across the US to the Canadian province of British Columbia.

Route description

[edit]
I-19 becomes an at-grade divided freeway just west of its southern terminus in Nogales. The US–Mexico border is just south of the Interstate (left of image).

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 Heroica Nogales, Mexico, via state-maintained surface roads, and connect with Federal Highway 15 (Fed. 15) either to the south or west of Nogales, Sonora.[3]

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 0.32 kilometers (0.2 mi) 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 and Heroica Nogales for travelers bound to or from Hermosillo or Mexico City and provides for the continuous flow of freight and truck traffic through the larger Nogales-Mariposa Port of Entry to Fed. 15, which has its northern terminus at the US–Mexico border with SR 189 and its southern terminus 2,179 kilometers (1,354 mi) away in Mexico City.[4] 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 in the Coronado National Forest.[3]

I-19 northbound at the I-10 interchange; the downtown Tucson skyline can be seen on the left.

Just before entering Tucson, I-19 passes through the eastern section of the San Xavier Indian Reservation 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.[3]

Nearly the entire route of I-19 follows, or is adjacent to, the former routing of US 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, southeast of Phoenix. 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

[edit]
I-19 Signage
Metric-unit advance guide sign on I-19, installed as part of the Valencia Road interchange renovation
Metric-unit advance guide sign on I-19, installed as part of the Valencia Road interchange renovation
Advance Guidance Sign alerting Drivers of I-19's Metric Signage located near Exit 99 (Southbound) for West Ajo Way SR 86
Advance Guidance Sign alerting Drivers of I-19's Metric Signage located near Exit 99 (Southbound) for West Ajo Way SR 86

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 (ADOT), metric signs were originally placed because of the push toward the metric system in the US at the time of the original construction of the highway.[5]

I-19 had originally been signed as it was constructed, in a series of small signing contracts that used customary units.[6] In 1980, ADOT awarded a single contract to install new signs which used metric units, to overlay customary-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" (1.2 mi) for distances over one kilometer (0.62 mi) and "500 m" (0.31 mi) for distances under one kilometer (0.62 mi), 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 88 km/h, which is a close soft-conversion of the then-existing 55 mph (88.51 km/h) national maximum speed limit. As Arizona's current maximum speed limit is 75 mph, the metric equivalent would most likely read 120 km/h (74.56 mph). 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.[7]

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.

As was the case in 1980, the signing plans were dimensioned in feet and inches.[8] However, a number of signs near the Valencia Road interchange were replaced or amended when it was converted from a partial cloverleaf interchange to a single-point urban interchange in 2000. One of these signs has a fractional kilometrage greater than one kilometer (0.62 mi), rendered as "1500 m" (0.93 mi), 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.[9]

Citing motorist confusion arising from the metric signs on I-19, ADOT's Tucson district announced that new signs on I-19 would use US customary units. 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.[10] 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.[11]

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 was completed in August 2004.[12]

History

[edit]

The first sections of I-19 to be opened to traffic were a 4.8-kilometer (3 mi) stub from I-10 to Valencia Road, in 1962 and a 3.2-kilometer (2 mi) stretch in Green Valley in 1963. The freeway between Rio Rico and Nogales 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 the entire I-19 project as "completed", which includes segments between Green Valley and Nogales.

Future

[edit]

I-19 is a very heavily traveled corridor in the Tucson metro area. The freeway is currently two lanes in both directions for most of its length, with the exception of the interchange with I-10 up until Irvington Road, where it transitions to four lanes. Current plans call for widening from Irvington Road to Valencia Road, bringing the freeway to three lanes in each direction.[13] Future plans include expansion to up to five lanes in each direction by 2030 from the crossing with I-10 to San Xavier Road.[14]

I-19 is also part of the proposed I-11 corridor between Nogales and Sahuarita.[15]

Exit list

[edit]
CountyLocationkm[1]miOld exit[16]New exitDestinationsNotes
Santa CruzNogales0.000.00 BL 19 (Grand Avenue) / Crawford StreetADOT defines this intersection as southern terminus; former US 89 / SR 93
0.280.17West StreetAt-grade intersection; south end of freeway; road continues as Compound Street
0.710.441AInternational StreetSouthbound exit only
1.901.181BWestern AvenueSigned as exit 1 northbound
4.762.9624 SR 189 (Mariposa Road)
​8.555.3158 BL 19 (Grand Avenue)Southbound left exit and northbound entrance; former US 89 / SR 93
Rio Rico12.427.72712 SR 289 (Ruby Road)
17.5310.891017Rio Rico Drive / Yavapai Drive
22.4513.951322Peck Canyon Road
25.1715.641525Palo Parado Road
Tumacacori-Carmen29.3418.231829Tumacacori-CarmenTumacácori National Historical Park
Tubac34.9421.712134Tubac
Tubac–Amado line40.1024.922440Chavez Siding Road
Amado42.8426.622742Agua Linda Road
48.3930.073048Arivaca Road
PimaGreen Valley56.2634.963456Canoa Road
63.6339.543963Continental Road
65.7440.854065Esperanza Boulevard
Sahuarita69.7243.324369Duval Mine RoadFormer US 89 / SR 93, I-19 BL; Titan Missile Museum
75.4846.904675Sahuarita Road
San Xavier Indian Reservation80.3249.914980Pima Mine RoadDesert Diamond Casino, Tohono O'odham Nation
87.9854.675487Papago RoadDead end, U-turn only
92.0457.195692San Xavier RoadAccess to Mission San Xavier del Bac
Tucson95.1059.095895 Valencia Road – TucsonTucson International Airport
98.3561.1198Irvington Road
99.9762.126199 SR 86 (Ajo Way)
101.6363.15—101
 I-10 east – El Paso		Northbound exit and southbound entrance; I-10 exit 260
101.8463.2810229th Street / 22nd Street / Silverlake Road / Starr Pass BoulevardNorthbound exit and southbound entrance
102.0863.43—
 I-10 west – Phoenix		Northern terminus; I-10 exit 260
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

Business routes

[edit]

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

[edit]
Interstate 19 Business marker
Interstate 19 Business
State Business Route 19 (1)
LocationNogales
Length5.88 mi[1] (9.46 km)
Existed1992–present[17]
Map
A map of the Nogales business loop. The route is highlighted in red.
I-19 Bus. (Grand Avenue) junction with SR 82 in Nogales

Interstate 19 Business (I-19 Bus.) begins at the Mexican border in Nogales near the southern end of the Interstate. 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.[1] The route follows the former alignment of US 89, SR 93, and SR 789, back when all three highways traversed through southern Arizona.[18] The route has been commissioned as I-19 Bus. since US 89 was decommissioned from southern Arizona in 1992.[17]

Major intersections
The entire route is in Santa Cruz County.

Locationmi[1]kmDestinationsNotes
Nogales0.000.00 Fed. 15 south – MexicoDennis DeConcini Port of Entry; international border with Mexico; continues south as Mexican Federal Highway 15
0.140.23
 I-19 north (Crawford Street) – Tucson		ADOT defines this intersection as southern terminus of I-19
1.662.67
 SR 82 east (Patagonia Highway) – Patagonia
2.774.46

 SR 189 south (Mariposa Road) to I-19
​5.889.46
 I-19 north		Northern terminus; no access to I-19 south
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

Sahuarita–Tucson loop

[edit]
Interstate 19 Business marker
Interstate 19 Business
State Business Route 19 (2)
LocationSouth Tucson–Green Valley
Length20.24 mi[2] (32.57 km)
Existed1992–2004[19][20]
Map
A map of the Tucson business loop. The route is highlighted in red.

Interstate 19 Business (I-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. 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 exit 261 and South 6th Avenue in South Tucson.[1] The route follows the former alignment of US 89, SR 93, and SR 789, back when all three highways traversed through southern Arizona.[18] The route was commissioned as I-19 Bus. since US 89 was decommissioned from southern Arizona in 1992.[19] In 2002, the state handed maintenance of I-19 Bus. between Los Reales Road and I-10 to the city of Tucson.[21] 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.[20]

Major intersections
The entire route was in Pima County.

Locationmi[2]kmDestinationsNotes
Green Valley43.8870.62 I-19 / West Duval Mine Road – NogalesSouthern terminus; I-19 Exit 69; road continues west as West Duval Mine Road
Sahuarita48.1577.49
 East Sahuarita Road to I-19
Tucson60.4197.22


 East Valencia Road to I-19 / I-10 / BL 10 – Tucson International Airport
63.50102.19

 SR 86 west (West Ajo Way) to I-19 / East Ajo Way – Ajo		Eastern terminus of SR 86
South Tucson64.12103.19 I-10 / South 6th Avenue – Casa Grande, El PasoNorthern terminus; I-10 Exit 261; road continues north as South 6th Avenue
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Interstate 19

View on Grokipedia
from Grokipedia
Interstate 19 (I-19) is a north–south Interstate Highway entirely within the U.S. state of , spanning 63.3 miles (101.9 km) from the international border crossing in Nogales to a junction with in Tucson. It functions as a primary freight and commerce corridor, facilitating trade between and the as part of the CANAMEX Trade Corridor and Arizona's Primary Freight Network. I-19 traverses Santa Cruz and Pima counties, connecting urban border areas with rural landscapes and serving both regional passenger traffic and heavy truck volumes. The highway's construction occurred in segments beginning in the early , with initial openings including a three-mile stub near Tucson in 1962 and further extensions through the and , achieving full completion by 1979. A distinctive feature of I-19 is its use of metric signage, the only such Interstate in the nation, where exit numbers and distances are marked in kilometers rather than miles—a legacy of early U.S. efforts to adopt the in the . This four-lane divided freeway includes 23 grade-separated interchanges, two ports of entry at the , and a U.S. Border Patrol checkpoint near milepost 25, contributing to its role in international logistics while managing high traffic volumes that reached up to 67,438 vehicles per day near Tucson in 2014. Ongoing improvements by the Arizona Department of Transportation (ADOT) address congestion, safety, and infrastructure needs, including variable speed limits, wrong-way detection technology with installation beginning in 2025 and expected completion in 2025/2026, and pavement rehabilitations completed between 1994 and 2014. With projected growing to over 101,000 vehicles by 2035 in the Tucson area, I-19 remains critical for economic connectivity in , supporting , produce transport, and cross-border .

Route description

Overview

Interstate 19 (I-19) is a north-south Interstate Highway located entirely within , with a total length of 102.08 km (63.43 mi), ranking it as the eighth-shortest primary (two-digit) Interstate in the . The route serves as a vital link between the U.S.- border and central , traversing Santa Cruz and Pima counties through a mix of rural, suburban, and urban landscapes. I-19 begins at West Crawford Street in Nogales, immediately north of the international border, and proceeds northward, ending at a interchange with (I-10) southeast of downtown Tucson. Along its path, the highway passes through key communities including Rio Rico, Green Valley, and Sahuarita, while paralleling the Santa Cruz River for much of its extent, which influences the surrounding riparian environment. The route features scenic vistas of the within the and lies in close proximity to Madera Canyon, a renowned area for and accessible via nearby exits. Terrain along I-19 transitions from rolling, mountainous sections near the border to the more level and expansive Tucson Basin as it approaches its northern terminus.

Signage

Interstate 19 features a distinctive signage system that employs metric units exclusively for measurements and exit numbering, while speed limits are posted in , creating a hybrid approach unique among U.S. Interstates. This setup includes mileposts marked in kilometers, with exits sequentially numbered based on kilometer s from the international border at Nogales, such as at the southern terminus and Exit 102 near Tucson. The metric signs, often with white lettering, are supplemented by informational plaques advising drivers of the metric usage, reinforcing I-19's status as the sole Interstate highway in the United States with fully metric for its primary route markers. The originated as part of a broader U.S. initiative under the 1975 , which established the U.S. Metric Board to promote voluntary adoption of the . Selected as a pilot project due to its proximity to and near-completion status, I-19's signage conversion began in the late 1970s, with full implementation of kilometer-based signs by 1980 through a contract awarded by the (ADOT). This made I-19 the first and only Interstate to use metric units for all distance signage and mileposts, aligning with international standards while the rest of the U.S. Interstate system retained customary units. Over time, challenges arose with the , leading to partial adjustments. In , ADOT replaced metric signs with mile-based ones on a short segment between Exits 99 (Ajo Way) and 101 (I-10) during the reconstruction of the I-10/I-19 interchange, citing driver familiarity and consistency as factors amid mixed public feedback. This reversion affected only a limited portion, preserving metric signage for the majority of the 102-kilometer route. In 2009, ADOT proposed a full conversion to miles, estimating costs at $1.5 million to replace approximately 400 signs using federal stimulus funds, primarily to standardize with national practices and address visibility issues with aging metric panels. The plan, which included temporary dual markings, faced significant opposition from local communities, businesses, and metric advocates who viewed the signage as a cultural and historical asset tied to the highway's border role. Petitions and public input led ADOT to halt the project in 2010, reallocating funds elsewhere and maintaining the metric system. As of 2025, I-19's signage remains predominantly metric, with the 2004 segment as the primary exception, though debates persist amid occasional federal reviews for . ADOT has confirmed no immediate changes are planned, attributing preservation to ongoing support that emphasizes the highway's unique identity.

Exit list

Interstate 19 features 25 numbered exits along its 101-kilometer length, with numbering based on kilometerposts starting from the U.S.- in Nogales and increasing northward to the interchange with in Tucson. The exits primarily connect to state routes, local roads, and frontage roads, serving communities such as Rio Rico, Tubac, Green Valley, Sahuarita, and Tucson; some are partial interchanges with limited access, and a few utilize frontage roads for local traffic. Approximate mile equivalents are provided for reference, calculated from the used on signage.
kmmi (approx.)LocationNorthbound DestinationsSouthbound DestinationsNotes
00.0NogalesEnd of freeway; West Crawford St., International BorderWest Crawford St., International BorderAccess to U.S.-Mexico border crossing; speed limit 45 mph northbound, 25 mph southbound; partial interchange with frontage roads.
1A0.6NogalesInternational St.International St.Partial interchange; local access in Nogales.
1B0.6NogalesWestern Ave.Western Ave.Partial interchange; connects to local roads and Target Range Rd.
42.5NogalesSR 189 south – Mariposa Rd., Mariposa Port of EntrySR 189 south – Mariposa Rd., Mariposa Port of EntryFull interchange; border truck route to Mexico; connects to SR 189 (state route).
85.0Rio RicoBL I-19 / Grand Ave., SR 82 east – Patagonia, SonoitaBL I-19 / Grand Ave., SR 82 east – Patagonia, SonoitaLeft exit northbound; full interchange; business loop and state route connection.
127.5Rio RicoSR 289 west – Ruby Rd., Nogales Ranger StationSR 289 west – Ruby Rd., Nogales Ranger StationFull interchange; state route to Peña Blanca Lake; located in Rio Rico.
1710.6Rio RicoRio Rico Dr., Yavapai Dr.Rio Rico Dr., Yavapai Dr.Full interchange; local roads with frontage road access in Rio Rico.
2213.7TubacPeck Canyon Rd.Peck Canyon Rd.Partial interchange; near U.S. Border Patrol checkpoint; local access.
2515.5TubacPalo Parado Rd.Palo Parado Rd.Full interchange; rural local road.
2918.0TumacácoriTumacácori, CarmenTumacácori, CarmenFull interchange; access to Tumacácori National Historical Park via local roads.
3421.1TubacTubacTubacFull interchange; local access to Tubac Presidio State Historic Park.
4024.9AmadoChavez Siding Rd.Chavez Siding Rd.Partial interchange; rural industrial access.
4226.1Green ValleyAgua Linda Rd.Agua Linda Rd.Full interchange; local road near Green Valley.
4829.8Green ValleyArivaca Rd.Arivaca Rd.Full interchange; enters Pima County; local road to Green Valley.
5332.9Green ValleyRest AreaRest AreaFacilities with parking and services; no road connection.
5634.8Green ValleyCanoa Rd.Canoa Rd.Full interchange; local road near Canoa Ranch.
6339.1ContinentalContinental Rd.Continental Rd.Full interchange; access to Madera Canyon Recreation Area.
6540.4SahuaritaEsperanza Blvd.Esperanza Blvd.Partial interchange; local boulevard access.
6942.9SahuaritaDuval Mine Rd.Duval Mine Rd.Full interchange; near Titan Missile National Historical Landmark; industrial access.
7546.6SahuaritaSahuarita Rd. – SahuaritaSahuarita Rd. – SahuaritaFull interchange; main access to town of Sahuarita via local road.
8049.7SahuaritaPima Mine Rd.Pima Mine Rd.Full interchange; 25 mph advisory speed; industrial mine access.
8754.1TucsonPapago Rd.Papago Rd.Full interchange; local road; speed limit changes to 65 mph northbound, 75 mph southbound.
9257.1San Xavier Indian ReservationSan Xavier Rd. – San Xavier MissionSan Xavier Rd. – San Xavier MissionPartial interchange; 25 mph advisory speed; access to San Xavier del Bac Mission.
9559.0TucsonValencia Rd. – Tucson International Airport, Pascua Yaqui PuebloValencia Rd. – Tucson International Airport, Pascua Yaqui PuebloFull interchange; major access to airport and tribal lands via arterial road.
9860.9TucsonIrvington Rd.Irvington Rd.Full single-point urban interchange; arterial road in Tucson.
9961.5TucsonSR 86 west – Ajo Way, Arizona-Sonora Desert Museum, Old TucsonSR 86 west – Ajo Way, Arizona-Sonora Desert Museum, Old TucsonFull single-point urban interchange; state route connection.
10162.8TucsonI-10 east – Las Cruces, El PasoI-10 east – Las Cruces, El PasoFull interchange; end of I-19 northward.
10263.4Tucson22nd St., 29th St., Starr Pass Blvd., Silverlake Rd., I-10 west – Phoenix22nd St., 29th St., Starr Pass Blvd., Silverlake Rd., I-10 west – PhoenixPartial interchange with frontage roads; collector-distributor ramps to I-10 west.

Significance

International trade

Interstate 19 provides a direct northbound connection from the Mariposa Land Port of Entry at the Port of Nogales, one of the busiest U.S.- border crossings for commercial traffic, which processed 404,588 northbound trucks in 2024. This linkage enables efficient freight movement from the border into , serving as a primary artery under the United States-Mexico-Canada Agreement (USMCA), the successor to NAFTA. The highway facilitates the transport of key goods such as fresh produce, electronics, and automobiles, with Nogales handling significant volumes of agricultural exports from , including fresh produce imports valued at $2.8 billion in 2024, alongside manufactured items like electrical components and vehicle parts. The economic contributions of Interstate 19 to are substantial, supporting job creation across , , and sectors in communities like Nogales, Rio Rico, and Tucson. By linking the border to , I-19 enables the distribution of cross-border to broader U.S. markets, bolstering regional and employment in transportation and operations. For instance, the corridor's role in helps sustain a bi-national that processes billions in , contributing to high-wage jobs in warehousing, trucking, and related industries, while also aiding agricultural distribution hubs in Nogales that employ thousands seasonally. Overall, trade through Nogales generated $34.1 billion in imports and exports in 2024, underscoring I-19's integral part in driving economic growth in the region. Despite these benefits, Interstate 19 faces challenges from border congestion, heightened security measures implemented post-9/11, and infrastructure strain due to rising trade volumes. Enhanced U.S. Customs and Border Protection protocols since 2001 have increased inspection times at Nogales, leading to frequent delays for commercial trucks and backups extending onto I-19, particularly during peak seasons for produce imports. These security enhancements, including expanded screening and staffing, have improved border safety but exacerbated congestion at the port, where wait times can exceed hours amid growing freight demands. Additionally, the highway experiences freight delays at inland checkpoints and urban bottlenecks near Tucson, straining the infrastructure designed for earlier trade levels and prompting calls for expansions to accommodate the $34.1 billion annual trade flow.

CANAMEX Corridor

Interstate 19 forms a critical component of the , a designated trade route established under the (NAFTA) in 1994 to enhance connectivity among , the United States, and . The corridor spans from in , , through major U.S. interstates and highways, to Nogales in , , promoting efficient cross-border by integrating highway infrastructure across the three nations. This multinational pathway was formalized in the National Highway System Designation Act of 1995, which identified it as High Priority Corridor 26 to support economic integration and freight mobility. As the southernmost segment within the U.S. portion of the , Interstate 19 connects the international border at , to Tucson, where it links directly to , enabling seamless northward freight movement toward Phoenix and beyond. This alignment facilitates the transport of goods, including produce and manufactured items, between and northern markets, underscoring I-19's strategic position in the corridor's overall network. The route's designation emphasizes its role in reducing bottlenecks and supporting high-volume trade flows across . Federal and state governments have invested significantly in enhancements, with funding directed toward intelligent transportation systems (ITS) to improve and safety along I-19 and connecting routes. These investments include deployment of real-time monitoring technologies and variable message signs to optimize vehicle flow, particularly for commercial trucks. Additionally, border facilitation technologies, such as automated clearance systems and electronic screening, have been prioritized to expedite cross-border operations at Nogales, aligning with broader corridor goals for efficient trade processing. The Arizona Department of Transportation (ADOT), in coordination with the (FHWA), has allocated resources for these upgrades as part of the corridor's high-priority status. The long-term vision for the emphasizes enhanced multimodal integration to boost continental trade efficiency, with rail lines running parallel to the for much of its length. This approach aims to complement freight with rail options, reducing congestion on routes like I-19 and supporting intermodal transfers at key hubs such as Tucson. Ongoing planning by the Coalition seeks to expand these synergies, fostering a more resilient and sustainable trade network across .

History

Planning and construction

The planning for Interstate 19 began in the 1950s as part of the broader established by the , which authorized a nationwide network of controlled-access highways to improve transportation efficiency and national defense mobility. The route was designated to connect near Tucson northward to the U.S.-Mexico border at Nogales, replacing segments of the older and enhancing commercial and border access in . Construction proceeded in phases due to the project's scale and terrain, with the initial segment—a three-mile stretch from to Valencia Road near Tucson—opening to traffic in December 1962. Subsequent sections followed, including a two-mile portion through the Green Valley area in 1963 and extensions southward in the mid-1960s, such as from Sahuarita Road to Green Valley in 1967–1968. Segments from Rio Rico to Nogales were completed between 1968 and 1971. The full 63-mile highway from Nogales to its junction with was finished and dedicated in 1978. The project was funded primarily through federal Interstate Highway aid, which covered 90% of costs under the system's financing structure, supplemented by state contributions from . Construction faced engineering challenges, including navigation of the rugged terrain in the Santa Cruz River valley near the border and multiple crossings of the Santa Cruz River itself, which required bridges and stabilization to handle seasonal flooding. The highway was designed as a four-lane divided freeway with full control of access, featuring grade-separated interchanges and frontage roads to minimize disruptions to local traffic and farmland.

Metric adoption

Interstate 19's adoption of the stemmed from the broader U.S. efforts in the . In 1975, Congress enacted the , which established the U.S. Metric Board to oversee a voluntary transition to metric units as the preferred measurement system. The Board identified the nearly completed Interstate 19 as an ideal pilot project for converting signage from imperial to metric units, given its proximity to the Mexican border, short length of 101.9 kilometers, and alignment with international standards to facilitate cross-border trade. This timing during the national metrication push positioned I-19 as a test case for broader imperial-to-metric transitions on U.S. roadways, making it the only continuous U.S. interstate with primary distance signage in metric units; other highways slated for conversion either implemented it partially or reverted after the metrication efforts faltered in the early 1980s. The kilometer-based signage was installed by the highway's full completion in 1978. The Arizona Department of Transportation (ADOT) awarded a single contract to erect new metric signs, including distance markers, exit numbers, and mileposts measured in kilometers rather than miles. This involved renumbering exits—for instance, shifting from mile-based to kilometer-based sequencing—and overlaying metric equivalents on some existing to facilitate the transition. These changes made I-19 the only U.S. interstate fully signed in metric units, reflecting the era's optimism for national metric adoption. Subsequent decades brought controversies over maintaining the amid shifting priorities. In 2004, ADOT partially switched to mile-based signage for a short segment near the interchange (between what are now kilometer exits 99 and 101) to ensure consistency with connecting highways, citing motorist confusion as a factor. More significantly, in 2009, ADOT proposed a full conversion to customary units, estimating costs at $1.5 million for replacing approximately 400 aging signs, driven by ongoing maintenance expenses and reports of driver disorientation. However, the plan faced strong opposition and was overturned by 2010 through legislative resistance and public campaigns from local communities and businesses that had adapted to kilometer-based addressing and signage. I-19's persistence as the primary metricated highway in the U.S. can be attributed to its short length, which deferred the costs of conversion, its border location aiding trade with metric-using Mexico, and this local adaptation, which stalled reversion attempts in the 2000s and 2010s. Preservation efforts have since emphasized I-19's metric signage as a unique educational tool and asset for cross-border commerce. Advocates, including residents and businesses in , highlighted its role in promoting metric familiarity for U.S. drivers and easing navigation for Mexican travelers, given the highway's direct link to . These campaigns successfully reinforced its retention, underscoring the cultural and practical value of maintaining this relic of the 1970s metric push near an international boundary. In 2025, the U.S. proposed switching to mile-based signage, but following pushback, ADOT stated in May 2025 that no changes were planned, preserving the .

Future developments

Widening projects

Recent widening projects on Interstate 19 (I-19) have focused on increasing capacity along the corridor south of Tucson to accommodate growing traffic volumes associated with and international commerce. One key initiative involves adding one general-purpose lane in each direction between Irvington Road (milepost 57) and San Xavier Road (milepost 61.9), which encompasses the segment from Irvington Road to Valencia Road (milepost 58.82). This expansion, part of the Irvington Road traffic interchange improvements, aims to enhance mobility and reduce congestion in the Tucson , with design anticipated to complete in fall 2025 and construction starting early 2026. The total estimated cost is $91.45 million. Further south, previous recommendations include widening I-19 to six lanes from Sahuarita Road (milepost 45.70) to Valencia Road, building on the original four-lane design to address capacity deficiencies identified in corridor studies. These projects are prioritized for future programming under ADOT's State Transportation Improvement Program (STIP), with implementation dependent on funding availability and traffic demand projections. enhancements integrated into these widenings include rehabilitations over 24.5 miles from milepost 39.5 to 63.7 and roadside improvements to mitigate run-off-road crashes, contributing to a crash modification factor indicating potential reductions in incidents. Planned efforts include a comprehensive expansion from San Xavier Road to the I-10 interchange (mileposts 56.3 to 63.0), where I-19 is planned to be widened ultimately to four general-purpose lanes in each direction, with interim phases adding to three lanes each direction (six total). Phase 3, covering Valencia Road to I-10 (mileposts 58.82 to 63), is programmed for design in fiscal year 2025 at a cost of $9.215 million, adding one lane each direction. Earlier phases, such as Ajo Way interchange reconstruction (Phase I, completed post-2014), have progressed, but mainline widening construction has not yet begun as of November 2025. The overall plan from the 2012 study envisions seven phases with a total estimated cost of $485.1 million, though current programming reflects scaled implementation dependent on funding, including from the Infrastructure Investment and Jobs Act (IIJA) of 2021. Full completion remains a long-term goal beyond 2030 given current timelines. Environmental considerations are integral to these projects, particularly given the corridor's proximity to sensitive habitats. For the San Xavier Road to I-10 expansion, mitigation measures address impacts to the Santa Cruz River, a protected Water of the U.S. under the Clean Water Act, including reconstruction of the Santa Cruz River bridge on Ajo Way, replacement of culverts at Rodeo Wash, and installation of new box culverts to maintain drainage capacity. A Section 404 Individual Permit is required due to disturbances exceeding 0.5 acres, with $4.0 million dedicated to environmental mitigations such as seeding and control. Broader corridor studies highlight the need for compliance with the State Wildlife Action Plan to protect linkages like the Tumacacori Santa Ritas, though specific wildlife crossings are not detailed in current phases; instead, alignment adjustments avoid critical habitats like Martinez Hill.

Sonoran Corridor

As an alternative to direct I-19 widening, ADOT is studying the Sonoran Corridor (SR 410), a proposed 20.47-mile access-controlled freeway connecting I-19 near Sahuarita (milepost 45) to I-10 south of Tucson International Airport. The project aims to relieve congestion on I-19 and I-10 by providing a new east-west route for freight and passenger traffic. Engineering and environmental studies are ongoing as of 2025, with public meetings held in May 2025 and survey results released in December 2024. Implementation depends on environmental clearance and funding, potentially advancing in the late 2020s.

I-11 integration

In December 2015, the Fixing America's Surface Transportation (FAST) Act, a federal transportation bill, designated Interstate 19 (I-19) as the initial segment of the proposed (I-11) corridor in . This designation aims to establish a continuous north-south interstate route extending from the United States-Mexico border at , northward through I-19 to Tucson, and eventually connecting to via existing highways like (I-10) and U.S. Route 93. The integration supports broader connectivity within the CANAMEX trade corridor by linking key freight pathways across the U.S. Southwest. Long-term plans for I-11 envision a northward extension from Tucson along I-10 toward Phoenix and Wickenburg, potentially spanning approximately 280 miles in Arizona alone before linking to Nevada segments. This expansion would enhance regional infrastructure by providing a dedicated high-capacity route for freight and passenger traffic, reducing reliance on congested urban arterials. The 2017 Arizona Department of Transportation (ADOT) I-19 Corridor Profile Study analyzed the existing I-19 alignment and recommended improvements such as interchange upgrades and safety enhancements to prepare the corridor for future I-11 integration, emphasizing its role in freight transport. As of November 2025, no construction has begun on the I-11 extension beyond the existing I-19 segment, with planning efforts focused on environmental reviews and route evaluations. The is currently reevaluating environmental impact statements for potential alignments, including options to co-locate with I-19 and I-10, amid ongoing legal and stakeholder consultations stemming from a January 2025 lawsuit settlement. These developments are expected to improve freight efficiency by streamlining cross-border trade flows and alleviating congestion on parallel routes like I-10.

Business routes

Nogales loop

Business Loop Interstate 19 (I-19) in Nogales, Arizona, is a 9.46 km (5.88 mi) loop route designated in 1992 following the decommissioning of U.S. Route 89 through the area. The route branches from the southern terminus of mainline I-19 at kilometer post 0 near Crawford Street and rejoins the freeway at kilometer post 4 north of the city center. The loop primarily follows Grand Avenue, the former alignment of U.S. 89, providing direct access to downtown Nogales and the Dennis DeConcini Port of Entry at the U.S.-Mexico border. This path supports local vehicular and pedestrian movement through commercial districts and historic areas, intersecting State Route 82 (Patagonia Highway) and State Route 189 (Mariposa Road) along the way. Designed as a bypass for urban traffic, the route diverts local and border-bound vehicles from the mainline I-19, which directs heavier commercial traffic to the nearby Mariposa Port of Entry. As of 2025, the business loop remains fully operational with standard Interstate Highway signage, including metric distance markers consistent with I-19, and has undergone no major modifications since its establishment.

Sahuarita–Tucson loop

Business Loop I-19 from Sahuarita to Tucson was a 20.24-mile (32.57 km) route that connected an interchange with I-19 near Green Valley at exit 69 (km 69 approximate) to near Tucson at exit 261 (km 101 approximate), primarily following the former alignment via Nogales Highway north through Sahuarita and transitioning to 6th Avenue in South Tucson. The loop provided essential access to emerging suburban areas and commercial developments along the corridor south of Tucson. Established in 1992 upon the truncation of northward to Flagstaff, the business loop replaced the decommissioned federal highway segments to maintain connectivity for local while I-19 served longer-distance travelers. Its original purpose focused on supporting in rapidly developing regions like Sahuarita, where it facilitated movement to and from the main interstate during the post-construction era of I-19, which had been fully opened since 1979. The route was decommissioned in 2004 by the Department of Transportation due to increasing redundancy, as the completed I-19 mainline effectively handled regional traffic volumes amid substantial urban expansion in the Tucson metropolitan area. Following removal, the alignment reverted to local roadways without any special state route designations, such as SR 19, and signage for the business loop was eliminated. Although no longer officially designated, the former loop's path continues to influence local development patterns in Sahuarita, having supported and commercial expansion during the and early ; as of 2025, it remains an unsigned local connector integrated into the regional road network.

References

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