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Interstate 19 Main route of the Interstate Highway System
Maintained by ADOT
Length:	63.60 mi[1] (102.35 km)
South end:	MX 15 at Mexican border at Nogales, AZ
North end:	I-10 in Tucson, AZ
State routes in Arizona < I-17 I-40 > Unconstructed - Former

Interstate 19 (I-19) is an intrastate Interstate Highway located entirely within the state of Arizona. I-19 runs from Nogales, at the Mexican border to Tucson, at Interstate 10.^[2]

Route description

In Nogales, Arizona, the southern terminus of I-19 is adjacent to the international port of entry, and southbound travelers can continue into Nogales, Sonora, Mexico, and connect with the northern terminus of Mexico Federal Highway 15. I-19 initially heads west through Nogales before making the turn to head north. It interchanges with two other state highways near the southern end of the route, SR 189 at exit 4 and SR 289 at exit 12. As I-19 enters the Tucson city limits, it has an interchange at SR 86 at exit 99 before reaching its northern terminus at a junction with I-10.

History

Nearly the entire route of I-19 follows, or is adjacent to, the former routing of U.S. Route 89 and the Santa Cruz River, which flows northward from Mexico, through Tucson and eventually disperses into the desert between Tucson and Phoenix. Most of the time, much of the river is dry, but heavy storms can cause it to overflow its banks.

The official "completion" date of the I-19 segment between Tucson (km 100) and Green Valley, Arizona (actually Helmet Peak Road at km 75) was February 12, 1972. A 1978 Project Report for the Arizona Department of Transportation lists entire I-19 project as "completed," which includes segments between Green Valley and Nogales, Arizona.

Metric-unit advance guide sign on Interstate 19, installed as part of the Valencia Road interchange renovation

Interstate 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 "metric system push" in the United States at the time of the original construction of the highway.

Interstate 19 had originally been signed as it was constructed, in a series of small signing contracts which used customary units.^[3] In 1980, Arizona DOT 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 kilometerposts, 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 1 km and "500 m" for distances under 1 km, 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 cancelled 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 "double nickel" national maximum speed limit. 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.^[4]

In 1999, Arizona DOT 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 kilomer. 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 Arizona DOT 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.^[5] However, a number of signs near the Valencia Road interchange were replaced or amended when it was converted from a partial cloverleaf to a SPUI in 2000. One of these signs has a fractional kilometrage greater than 1 km, 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.^[6]

Citing motorist confusion arising from the metric signs on I-19, Arizona DOT's Tucson district announced that new signs on I-19 would use United States 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.^[7] New signs were put into place between Exit 99 (Ajo Way) and Exit 101 (Interstate 10) in 2004 after the completion of the new Interstate 10–Interstate 19 interchange.

A recent reconstruction project at the Interstate's northern terminus with Interstate 10 in Tucson, Arizona (at the interchange commonly called "The Crossing") was begun in 2002 and completed in August 2004.^[8]

Exit list

County	Location	Kilometer (Mile)[1]	#	Destinations[9]	Notes
Santa Cruz	Nogales	0.00 (0.00)	Mexico – United States border
		1.90 (1.18)	1	Western Avenue (Target Range Road)
		4.76 (2.96)	4	SR 189 Mariposa Road
		8.55 (5.31)	8	I-19 Bus. south Grand Avenue (Business 19 not explicitly signed)	Southbound exit only
		12.42 (7.72)	12	SR 289 Ruby Road
		17.53 (10.89)	17	Rio Rico Drive, Yavapai Drive
		22.45 (13.95)	22	Peck Canyon Road
		25.17 (15.64)	25	Palo Parado Road
		29.34 (18.23)	29	Carmen, Tumacacori (Santa Gertrudis Lane) – Tumacacori National Historical Park
		34.94 (21.73)	34	Aliso Spring Road
		40.10 (25.92)	40	Chavez Siding Road
		42.84 (26.62)	42	Agua Linda Road
		48.39 (30.07)	48	Arivaca Road
Pima		56.26 (34.96)	56	Canoa Road
	Green Valley	63.63 (39.54)	63	Continental Road
		65.74 (40.85)	65	Esperanza Boulevard
		69.72 (43.32)	69	I-19 Bus. north / Duval Mine Road (Business 19 not explicitly signed)
	Sahuarita	75.48 (46.90)	75	Helmet Peak Road, Sahuarita Road
	San Xavier Indian Reservation	80.32 (49.91)	80	Pima Mine Road
		87.98 (54.67)	87	Papago Road
		92.04 (57.19)	92	San Xavier Road
	Tucson	95.10 (59.09)	95	Valencia Road – Tucson International Airport
		98.35 (61.11)	98	Irvington Road
		99.97 (62.12)	99	SR 86 Ajo Way
		102.?? (63.15)	101	I-10 – Phoenix, El Paso
		102.?? (63.28)	102	29th Street-22nd Street, Silverlake Road, Starr Pass Boulevard	Northbound exit & southbound entrance

See also

Business routes

• Interstate 19 Business from Green Valley to Sahuarita
• Interstate 19 Business in Nogales, Arizona, runs from Nogales to the Mexican border.

References

External links

• Arizona Roads

Main Interstate Highways (major interstates highlighted)
4	5	8	10	12	15	16	17	19	20	22	24	25	26	27	29	30
35	37	39	40	43	44	45	49	55	57	59	64	65	66	68	69
70	71	72	73	74	75	76 (W)		76 (E)		77	78	79	80	81	82
83	84 (W)		84 (E)		85	86 (W)		86 (E)		87	88 (W)		88 (E)		89	90
91	93	94	95	96	97	99	(238)		H-1		H-2		H-3
Unsigned			A-1		A-2		A-3		A-4		PRI-1		PRI-2		PRI-3
Lists		Primary			Main - Intrastate - Suffixed - Future - Gaps
		Auxiliary			Main - Future - Unsigned
		Other			Standards - Business - Bypassed