Interstate 15

Major cities; Bolded cities are officially-designated control cities for signs
	San Diego, California (southbound); Riverside, California (northbound; via SR 91 east); San Bernardino, California (southbound; via I-215 south); Los Angeles, California (southbound; via I-10 west); Barstow, California (California only, Nevada uses Los Angeles as the control city south of Las Vegas); Baker, California (As seen on signs between Barstow and Baker); Las Vegas, Nevada; St. George, Utah; Provo, Utah; Salt Lake City, Utah; Ogden, Utah; Pocatello, Idaho; Idaho Falls, Idaho; Butte, Montana; Helena, Montana; Great Falls, Montana; Shelby, Montana; Lethbridge, Alberta (northbound);

Route information
Length	1,433.52 mi (2,307.03 km)
Existed	1957–present
Major junctions
South end	I-8 / SR 15 in San Diego, CA
	Lua error in Module:Jct at line 204: attempt to concatenate local 'link' (a boolean value). in Ontario, CA; Lua error in Module:Jct at line 204: attempt to concatenate local 'link' (a boolean value). in Barstow, CA; US 95 in Las Vegas, NV; Lua error in Module:Jct at line 204: attempt to concatenate local 'link' (a boolean value). near Cove Fort, UT; Lua error in Module:Jct at line 204: attempt to concatenate local 'link' (a boolean value). in Salt Lake City, UT; Lua error in Module:Jct at line 204: attempt to concatenate local 'link' (a boolean value). near Butte, MT
North end	Highway 4 at Canadian border near Sweetgrass, MT

Template:Redirect6 Interstate 15 (I-15) is the fourth-longest north-south transcontinental Interstate Highway in the United States, traveling through the states of California, Nevada, Arizona, Utah, Idaho, and Montana. The Idaho, Utah and Arizona portions have been officially designated the 'Veterans Memorial Highway'.^[2]

Since I-15's inception, it has served as a long-haul route for North American commerce. It is now officially chartered for this purpose. From the junction of Interstate 515 in Las Vegas 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.^[3]

Local portions were built to connect the Inland Empire with San Diego in California, facilitate tourism access to Las Vegas, interconnect all of the Metropolitan Statistical Areas in Utah except Logan, and provide freeway bypasses for Pocatello, Idaho Falls, and Great Falls.

Since I-15's initial construction, California, Nevada, and Utah have consistently ranked in the fastest growing areas of the United States. As a result, the I-15 corridor 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 Utah's population^[4], 19 percent of California's population, and more than 70 percent of Nevada's population^[5] live in counties where Interstate 15 is the primary transportation corridor. Similarly, in California, I-15 is seeing more commuter traffic due to the growth of the Mojave Desert communities of Victorville and Barstow, California. In all of these states, I-15 has recently been or is currently in the process of being upgraded to increase capacity.^[6]^[7]^[8] The Arizona, Idaho and Montana portions have retained their rural, long-haul character. Although Arizona has also grown substantially since I-15's inception, I-15 only serves an isolated corner of the state.

Due to this rapid area growth, the I-15 corridor is the focus of several mass transit projects. The Las Vegas Monorail, FrontRunner commuter rail system and TRAX light rail in Salt Lake City 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 route; in 2004 the California-Nevada Interstate Maglev project held public meetings on the plan.^[9]

Route description

Lengths
	mi	km
CA	287	462
NV	124	200
AZ	29	47
UT	401	645
ID	196	315
MT	396	637
Total	1,433	2,307

This highway's southern terminus is in San Diego, California at Interstate 8, 18 miles (29 km) north of the international border with Mexico. However, work is being done to extend this to Interstate 5. The current work on this extension is signed State Route 15. There is a continuous freeway between I-8 and I-5, but various intersections and acceleration/deceleration lanes are not up to Interstate Highway standards. The northern terminus is in Sweetgrass, Montana at the international border between the United States and Canada, where it becomes Alberta Highway 4.

California

North of its junction with the Riverside Freeway, State Route 91, in the Inland Empire near Corona, the route roughly follows the former routes of U.S. Highway 91 and U.S. Highway 395. North of Devore, the highway follows the approximate alignment of historic U.S. Highway 66 along with U.S. 91 and 395. U.S. 395 breaks away at Hesperia and the route continues the approximate route of co-signed 66 and 91 until about the Mojave River, 35 miles (56 km) to the north. At that point, I-15 follows the old route of U.S. 91 exclusively. For many parts of the highway, high-voltage power lines, like Path 46 and Path 27, almost all from the Hoover Dam, follow the freeway. Many of these link distant power stations to the Los Angeles metropolitan area.

The starting point of Interstate 15 was originally planned to be in San Bernardino at an interchange with the San Bernardino Freeway, I-10. 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. However, legislation was later passed to extend the interstate to San Diego. But instead of extending the existing freeway from the I-10 interchange south, the California Department of Transportation made 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 15 miles (24 km). Then, in Fontana/Rancho Cucamonga, its directional alignment shifts to north-south where it eventually junctions with Interstate 10 (about 15 miles (24 km) or 24 kilometers 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 re-numbered as Interstate 215. Note that during the construction of I-15's present alignment, and for some time afterwards, I-215 was numbered as I-15E, and its actual mileage would begin at Interstate 10.

Nevada

Interstate 15 begins in Primm, continues through Las Vegas along the Las Vegas Strip corridor. Then the interstate crosses the border with Arizona in Mesquite. The whole interstate in Nevada runs entirely in Clark County, for a distance of 123.77 miles (199.19 km).

Arizona

I-15 just clips the northwestern corner of Arizona with a total length of 29.4 miles (47 km).^[10] The stretch is separated from the rest of the state and has one major exit, at Beaver Dam/Littlefield, Arizona. It includes a spectacular section where the road twists between the narrow walls of the Virgin River Gorge.

Utah

I-15 continues through Utah for just over 400 miles (640 km). It is the main north-south connection for the state. The highway approximately follows the old alignment of U.S. Highway 91 from St. George to Brigham City. The highway passes through the fast-growing Dixie region, which includes St. George, Cedar City, and eventually most of the major cities and suburbs along the Wasatch Front, including Provo, Orem, Sandy, West Jordan, Salt Lake City, Layton, and Ogden. Near Cove Fort, Interstate 70 begins its journey eastward across the country. The interstate merges with I-80 for about 3 miles (5 km) from South Salt Lake to just west of Downtown Salt Lake City and also merges with Interstate 84 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 when it passes through the mountains south of Cedar City and again north of Cove Fort.

Idaho

I-15 passes through Idaho for nearly 200 miles (320 km). The highway runs through Pocatello, Blackfoot, and Idaho Falls, intersecting with Interstate 86.

Montana

Interstate 15 continues onward through nearly 400 miles (640 km) of Montana through the cities of Butte, Helena and Great Falls, intersecting with Interstate 90, Interstate 115 and Interstate 315. At Sweetgrass, I-15 terminates upon crossing the international border into Alberta, Canada; however, I-15 signage is present on Alberta Highway 4 southbound from Lethbridge to the U.S.-Canada Border.

History

Plaque located on Interstate 15 between Helena and Great Falls.

Interstate 15 was constructed along the route of U.S. Route 91. Once Interstate 15 was relatively intact U.S. 91 was decommissioned, except for one part in Northern Utah/Southern Idaho where Interstate 15 instead followed the route of former U.S. Route 191.

Interstate 15 had an eastern branch bypassing San Bernardino, California, and a western branch in Idaho. I-215 around San Bernardino was I-15E^[11], and the western I-86 was once called I-15W.^[12]

Future

Redesignation of SR 15 in San Diego as I-15 will eventually occur when the freeway's interchange with SR 94 is updated to Interstate standards. The interchange currently has left-exits and blind merges, and is due to be updated with a long-awaited widening of SR 94 in 2008. At that time SR 15 will be resigned as part of I-15.