Interstate 15 (I-15): Route, Miles by State and Safety Data

How long is I-15?

FHWA's Route Log gives I-15 1,438.61 miles as of January 2026, which ranks it 10th among Interstates, just behind I-94. Wikipedia and Interstate Guide both print 1,433.52 miles.

The overlap notes show the Route Log credits I-15 with the pavement it shares with I-80 in Salt Lake City (3.31 miles) and I-84 between Riverdale and Tremonton (35.98 miles), so the Utah row includes both. The 7.65 miles it shares with I-90 at Butte are booked to I-90 instead. Most of the gap between the two totals sits in Utah, where the Route Log lists 405.71 miles and Wikipedia's state table lists 401.07. The other five states differ by less than half a mile each.

Where I-15 starts and ends

The southern end is at I-8 in San Diego's Mission Valley, where the freeway keeps going south as State Route 15 toward I-5. The northern end is the Sweetgrass-Coutts border crossing in Sweet Grass, Montana, where the road enters Canada as Alberta Highway 4 and continues toward Lethbridge.

Northbound, I-15 passes Escondido and Temecula, climbs Cajon Pass to a 4,260-foot summit, and crosses the desert through Victorville and Barstow to Mountain Pass and the Nevada line at Primm. After Las Vegas and Mesquite it cuts across the northwest corner of Arizona in the Virgin River Gorge, then covers Utah from St. George through Provo, Salt Lake City and Ogden. In Idaho it serves Pocatello and Idaho Falls before topping Monida Pass on the Montana line. At 6,870 feet that pass is the highest point on the route. Butte, Helena and Great Falls are the main Montana cities on the way to the border.

Interstate junctions along I-15

The list starts in San Diego, where I-15 begins at I-8, and works north. I-40 begins at I-15 in Barstow, and I-70 begins at it near Sulphurdale, on the Beaver-Millard county line in Utah. I-84 appears twice because it joins I-15 at Riverdale and leaves it at Tremonton, and I-90 shares about eight miles with I-15 at Butte. In Las Vegas, I-11 and US 95 meet I-15 at the Spaghetti Bowl just west of downtown.

Fatal crashes on I-15

From 2020 to 2024, 614 fatal crashes on I-15 killed 709 people, about 142 a year. That is 9.8 deaths per 100 route miles each year, a shade above the Interstate average of 9.5, and it places I-15 21st of 56 ranked routes.

The rate falls state by state from south to north. California is highest at 24.5, then Nevada at 17.0, Arizona at 9.5, Utah at 7.7, Idaho at 4.5 and Montana at 1.8. California and Nevada together account for 457 deaths on about 411 miles. San Bernardino County had 222 deaths, close to a third of the route total, and every one of Nevada's 105 deaths was in Clark County.

Deaths peaked at 180 in 2021 and fell in each later year, to 119 in 2024, the lowest of the five.

Counties with the most I-15 crash deaths

Bridges on I-15

The 2025 National Bridge Inventory counts 1,211 bridges on the I-15 main line, and only 13 rate Poor, about 1 percent. Idaho has the most of those, 6 of its 119 bridges, and Arizona's 29-mile segment has 3 Poor bridges out of 19. Utah has the most bridges on the route, 397, with 1 rated Poor. Half the bridges on I-15 date from 1975 or later.

In Utah County, a design-build project widened 24 miles of I-15 from Lehi to Spanish Fork, rebuilt 63 bridges and finished on December 15, 2012, at a final cost of $1.465 billion.

Tolls on I-15

A trip on I-15 from end to end in the general lanes is toll-free. FHWA's January 2023 inventory lists two tolled facilities on it, and both are optional express lanes next to free lanes. SANDAG runs the I-15 Express Lanes in San Diego County, where solo motorists with FasTrak pay a price that changes with traffic and carpools ride free. UDOT runs the express lanes along the Wasatch Front.

Both systems have grown past what the inventory shows. Riverside County opened express lanes on I-15 from Cajalco Road in Corona to near State Route 60 in 2021, and Utah began tolling a Layton-to-Riverdale extension on October 31, 2022, bringing its lanes to about 82 miles each way from Spanish Fork. The facility miles in the table are FHWA's figures for each lane system and can differ from the tolled length of I-15 itself.

I-15 auxiliary routes

I-15 has three three-digit routes, and one number, I-215, is used in three states. California's 55.08-mile I-215 leaves I-15 at Murrieta, passes through Riverside and San Bernardino and rejoins it at Devore; it was signed I-15E until AASHTO approved the new number in 1982. Utah's 29-mile I-215 serves Salt Lake City, Millcreek, Holladay and Cottonwood, and Nevada's 11.71 miles run through Henderson and Las Vegas. Montana has the two shortest: I-115 runs 1.2 miles into Butte and I-315 runs 0.83 miles into Great Falls.

How I-15 came together

I-15 was established on August 14, 1957, with its southern end planned near San Bernardino. The 1968 federal expansion of the Interstate system added an extension to San Diego, and AASHO confirmed it on June 24, 1969. In Idaho, a branch first numbered I-15W was approved as I-86 in 1977.

The Virgin River Gorge section in Arizona opened on December 14, 1973, and Nevada finished its last pieces, in North Las Vegas and near the Arizona line, in 1974. Montana wrapped up construction in 1988. The final link in the whole route, a bypass of Plymouth, Utah, opened on November 20, 1990.

Utah rebuilt 16.2 miles between Salt Lake City and Sandy starting in April 1997 and finished in 2001, ahead of the 2002 Winter Olympics. That job cost $1.63 billion and included about 130 bridges. Earlier, in 1975, UDOT built a wildlife overpass near Beaver that the Utah Division of Wildlife Resources considers the first in the United States.

I-15 traffic and road conditions

Searches for I-15 closures and crashes jump whenever something shuts the road, and the fastest answer comes from the state that manages that stretch. Their traveler sites are below, from California north to Montana.

I-15 questions