Interstate 25 (I-25): Las Cruces to Buffalo Route, Miles and Crash Data

How long is I-25?

The FHWA Route Log gives I-25 1,060.58 miles as of January 2026, which ranks 13th among Interstates. New Mexico holds the longest piece at 461.74 miles. Wyoming's 300.25 miles edge out Colorado's 298.59 by less than two miles.

Wikipedia, which cites the same FHWA table, and Interstate Guide both print 1,061.67 miles. Their state figures run a little higher, by 0.70 mile in Wyoming and 0.38 in New Mexico, so they appear to come from an older edition. Shared pavement does not explain the gap. The Route Log has no overlap notes for I-25 and books all of its miles to I-25 itself.

Where I-25 starts and ends

I-25 begins at the I-10 interchange at exit 144 in Las Cruces, just south of the New Mexico State University campus. US 85 joins it there and stays with it the length of New Mexico. The road ends at I-90 and US 87 in Buffalo, Wyoming.

Northbound, it passes Socorro, Belen and Los Lunas before Albuquerque, then tops Glorieta Pass southeast of Santa Fe at 7,452 feet and Raton Pass at 7,798 feet on the way into Colorado. In Colorado it links Trinidad, Walsenburg, Pueblo, Colorado Springs, Castle Rock, Denver and Fort Collins, crossing the Palmer Divide at Monument Hill between the Springs and Denver. Cheyenne and Casper are the Wyoming cities. Albuquerque calls its stretch the Pan-American Freeway, and in Denver the road follows the South Platte River as the Valley Highway. The whole route is High Priority Corridor 27, the Camino Real.

Interstate junctions along I-25

Read from Las Cruces north, the list opens with I-10 at the southern end and I-40 at the Big I in Albuquerque. Colorado adds I-70 and I-76. In Wyoming, I-25 meets I-80 at Cheyenne and closes at I-90 in Buffalo. Between I-40 in Albuquerque and I-70 in Colorado, no other main Interstate crosses it.

Fatal crashes on I-25

Fatal crashes on I-25 killed 431 people from 2020 to 2024, about 86 a year. The yearly count went from 76 in 2020 to a high of 102 in 2022, then fell back to 83 in 2023 and 85 in 2024. Spread over the route's length, that is 8.1 deaths per 100 route miles a year, under the Interstate average of 9.5. I-25 ranks 28th of the 56 routes long enough to have a rate.

Colorado had 196 deaths and New Mexico 195, nearly a tie, but Colorado's come from 298.59 miles against New Mexico's 461.74. That gives Colorado a rate of 13.1 and New Mexico 8.4. Wyoming's 40 deaths over 300.25 miles work out to 2.7. El Paso County, Colorado, which contains Colorado Springs, leads every county on the route with 49 deaths. Bernalillo County, around Albuquerque, follows with 45, and then comes Socorro County, New Mexico, with 39. Pueblo County has 34 and Santa Fe County 27.

Counties with the most I-25 crash deaths

Bridges on I-25

The 2025 National Bridge Inventory counts 1,044 bridges on the I-25 main line, and half of them date from 1968 or earlier. Most, 721, rate Fair. Only 34 rate Poor, about 3.3 percent, and Wyoming has 20 of those even though it has the fewest bridges of the three states, 296. New Mexico has 12 Poor bridges out of 417. Colorado has 2 out of 331.

In early December 2025 CDOT finished the Greenland wildlife overpass near Larkspur, a deck 200 feet wide and 209 feet long over the six lanes of I-25. CDOT calls it the largest wildlife overpass in North America, and it works with five underpasses and fencing nearby. Before they were built, this stretch averaged one wildlife collision a day during the spring and fall migrations, and CDOT expects that number to fall by 90 percent.

Tolls on I-25

FHWA's toll inventory dated January 1, 2023, lists two facilities on I-25, both priced express lanes in the Denver area. Plenary Roads Denver operates the stretch between 20th Avenue downtown and US 36 at Kalamath Street. The Colorado Transportation Investment Office picks up at US 36 and continues to E-470 and the Northwest Parkway. FHWA gives them 7.0 and 11.0 miles; those are facility lengths from the inventory and may not line up exactly with the tolled miles of I-25. Both are optional, and a trip from Las Cruces to Buffalo in the regular lanes costs nothing.

That inventory leaves out two newer express lane projects. The 18-mile South Gap lanes between Monument and Castle Rock opened on December 10, 2021, and began charging in January 2024. Prices there change with the time of day, and vehicles carrying three or more people ride free with a switchable transponder set to HOV. To the north, CDOT opened 14 miles of express lanes from Berthoud to Fort Collins for testing in late 2023 and started charging on April 7, 2026. With an ExpressToll pass, each segment costs $1 to $4.75. Six more miles, from Mead to Berthoud, are still under construction.

I-25 auxiliary routes

I-25 has a single three-digit route. I-225 covers 12.46 miles in the Denver-Aurora area and connects I-25 with I-70. It opened over its full length on July 21, 1976, and Denver's T-REX project later widened I-25 to ten lanes from the I-225 junction south to C-470.

Building I-25, state by state

The first piece of Denver's Valley Highway, from Evans Avenue to 52nd Avenue, opened on November 23, 1958. Colorado finished its share in 1969, when the last 21 miles between Trinidad and Walsenburg were dedicated on September 21. New Mexico began with a section from Socorro to Belen and completed its upgrade of the old US 85 corridor in 1980. Wyoming, where the freeway replaced stretches of US 87, built its section from 1958 to 1982, the latest of the three.

The big city rebuilds came after 2000. Albuquerque's Big I, the I-25 and I-40 interchange first opened in 1966, was rebuilt as a five-level interchange between June 30, 2000, and May 25, 2002, for about $293 million. Denver's T-REX began in September 2001, cost $1.67 billion, added light rail and wrapped up in 2006, 22 months ahead of schedule. The COSMIX widening through Colorado Springs was done by December 2007.

I-25 traffic and road conditions

Winter storms sometimes close I-25 in both directions on Raton Pass, and Monument Hill between Denver and Colorado Springs is known for blizzards and high winds. For closures and crashes on the road today, use the traveler site of the state you are driving in. They are listed from New Mexico north to Wyoming.

I-25 questions