Interstate 25

I-25 New Mexico I-25 Colorado I-25 Wyoming
North End
South End
I-25 south - Greenwood Village, CO

Growth along Interstate 25 in Colorado expands the freeway to ten plans plus two auxiliary lanes through Greenwood Village. 08/11/16


Interstate 25 follows the Front Range of the Rocky Mountains joining the capital cities of Santa Fe, Denver and Cheyenne. I-25 also serves Albuquerque, New Mexico’s largest city and Pueblo and Colorado Springs in central Colorado. Suburban growth along the corridor may someday join the Denver and Colorado Springs metropolitan areas. HO/T lanes (North I-25 Express Lanes) accompany the freeway from 20th Street at Downtown Denver to Adams County, north of I-270 and south of Thornton.

High Priority Corridor

Interstate 25 is part of High Priority Corridor 27: Camino Real for its entire length.

Parallel U.S. Routes

Interstate 25 replaced all of U.S. 85 from Las Cruces, New Mexico, north to Denver, Colorado. The freeway also replaced U.S. 87 from Raton, New Mexico, northward to its terminus in Buffalo, Wyoming with the exception of a parallel stretch between Glenrock and Casper. U.S. 85 parallels the freeway again in the Cheyenne vicinity. These U.S. routes are generally not co-signed in New Mexico or Colorado, but U.S. 85 and U.S. 87 are well-signed in Wyoming.

Other overlaps with U.S. routes in New Mexico include U.S. 60 north from Socorro, U.S. 285 near Santa Fe, U.S. 84 from Santa Fe east to Las Vegas and U.S. 64 at Raton. Within the Centennial state, U.S. 160 accompanies I-25 north from Trinidad to Walsenburg and U.S. 24 overlays I-25 at Colorado Springs. Within Wyoming, U.S. 26 runs in tandem with I-25 west from Dwyer to Glenrock while U.S. 20 ties in from Orin to Glenrock.


Interstate 25 through New Mexico replaced or directly overlaid all of U.S. 85 from Las Cruces north to the Colorado state line north of Raton. The first section to open ran from Socorro to Belen. Overall upgrades to U.S. 85 for I-25 were completed through the state in 1980.1

The Big I

The Big I Interchange is the crossroads where I-25 and I-40 meet northeast of Downtown Albuquerque, New Mexico. The original exchange between the two freeways was known as “The Crossroads of the Southwest.”2 Opened to traffic in 1966,3 the directional interchange with left side ramps was constructed on the premise of moving military personal and other long distance traffic through the Albuquerque metropolitan area. Daily commuter traffic interests were not factored into the original interchange design.2 As as a result, the previous interchange was designed to handle 40,000 vehicles per day (vpd), but increasing traffic congestion and weaving traffic patterns eventually plagued the exchange, which served 300,000 vpd by 2000.3

The “Big I” construction built a five-level systems interchange connecting I-25 with I-40. The three phase reconstructed sections of I-40 and I-25 within 1.5 miles of the Big I. This included straightening out the S-curve along I-25 that previously passed under Candelaria Road.  High speed flyovers replaced left side ramps and both freeways were expanded by one lane per direction. Additionally the adjacent frontage road system was completed and expanded to improve traffic flow through the Big I area along I-40 and the nearby Santa Barbara-Martineztown neighborhood.4 Ultimately costing $293 million,5 work on the Big I interchange kicked off on June 30, 2000 and concluded on May 25, 2002.3 The construction contract was valued at $222 million, while the design, construction engineering, and property acquisition made up the bulk of the added costs.5

Colorado Springs Metropolitan Interstate Expansion: COSMIX

Interstate 25 was also improved through the Colorado Springs area. As of March 2006, the Holland Park Noise Barrier and bridges over Ellston Street were completed. Projects continued to include widening and modernization of the freeway at the Bijou Interchange/Colorado Avenue, from Fillmore Street to Garden of the Gods, the section near North Nevada Avenue (Business Loop I-25) and Rockrimmon, and from Woodmen to North Academy. Completion of Colorado Springs Metropolitan Interstate Expansion (COSMIX) occurred by December 2007.


The largest multi-modal transportation project in Colorado history, T-Rex, started in September 2001. With origins dating back to 1944, the predecessor of Interstate 25 was the Platte Valley Drive Road. The $33 million project broke ground on November 16, 1948 and encompassed 11.2 miles. The road became known as the Valley Highway. Between Evans Avenue and 52nd Avenue, the freeway opened on November 23, 1958. Traffic counts topped at 33,000 vpd. By 1964, construction commenced for Interstate 225 with a design capacity of 50,000 vpd. This freeway opened fully between Interstate 70 and Interstate 25 on July 21, 1976. Both facilities were well over capacity with the Valley Highway at 230,000 vpd and Interstate 225 at 120,000 vpd in 1998. Traffic volumes were consistent in both directions of travel. This was based upon the fact that Denver has two major employment hubs: the Central Business District to the north and the Southeast Business District to the south. These factors set the tone for the T-REX construction project.

T-REX stands for Transportation Expansion Project and involves the Interstate 25/225 corridors. In 1992 studies began on how to handle the burgeoning transportation woes the Valley Highway entailed. The problem resulted in the partnership of the Colorado Department of Transportation (CDOT) and the Regional Transportation District (RTD), which is responsible for the Denver light rail system. The two agencies commissioned the Southeast Corridor Major Investment Study (MIS) to handle the growing dilemma. By 1995 several options were in consideration. They included the construction of new freeway lanes, the double-decking of existing freeway lanes, and construction of heavy rail, construction of monorail, and various other mass transit related options. By 1997 the Denver Regional Council of Governments (DRCOG) adopted the MIS recommendations. Those included 19.7 miles of new double-track light rail, 13 new light-rail stations, expansion of travel lanes to coincide with interchange improvements and bridge replacement projects, and HOV lanes among other concepts. Environmental Impact Studies, commenced in 1998, were completed in 18 months. Funding issues were addressed in 1999 and a Record of Decision signed in March 2000.6

Route Information

  • North End – Buffalo, WY

  • South End – Las Cruces, NM

  • Branch Routes – 1

  • Total Mileage – 1,061.67


New Mexico – 462.12

  • Cities – Las Cruces, Socorro, Belen, Albuquerque, Santa Fe, Las Vegas, Raton

  • Junctions

Colorado – 298.60

  • Cities – Trinidad, Pueblo, Colorado Springs, Denver, Longmont, Loveland, Fort Collins

  • Junctions

Wyoming – 300.95

  • Cities – Cheyenne, Douglas, Casper, Buffalo

  • Junctions

Source: December 31, 2021 Interstate Route Log and Finders List

I-25 Annual Average Daily Traffic (AADT)

Location Vehicles per day
Cheyenne, WY 23,675
Douglas, WY 9,137
Casper, WY 22,111
Buffalo, WY 2,894
Central New Mexico - 1972
Interstate 25 through north central New Mexico – 1972.

Through traffic along Interstate 25 between Albuquerque and Santa Fe utilized a multi-lane divided stretch of U.S. 85. Completion of the freeway in New Mexico in 1980 led to the removal of all signs for U.S. 85 in the Land of Enchantment.

Southern Colorado - 1968
All of Interstate 25 was complete from Walsenburg north to Wyoming by 1968. This excerpt was taken from the 1968 Colorado Official Highway Map.

The final section of I-25 to open in Colorado was a 21 mile segment between Trinidad and Walsenburg. It was dedicated on September 21, 1969.

I-25 south at E-470 / C-470 - Lone Tree, CO
Approaching the E-470 toll road and C-470 on Interstate 25 south at Lone Tree, Colorado. E-470 provides an eastern bypass for Interstate 25 around the Denver metropolitan area. The 47 mile long beltway uses all electronic tolling (AET). Photo taken 08/11/16.
Eastern Wyoming - 1964
1964 Wyoming Official Highway Map

Short segments of Interstate 25 were open to traffic in Wyoming by 1964:

  • Missile Drive (Exit 10) to the U.S. 85 split at Exit 17 (1958)
  • A three mile segment north of Chugwater (1959)
  • Fletcher Park Road to south of Glendo (1961 and 1962)
  • West Douglas to East Glenrock (1959 and 1962)
  • Yellowstone Highway to Bypass U.S. 20/26 in Casper(1960 and 1961)
  • North Terry Draw to south of Kaycee (1960)

Interstate 25 was expanded to four lanes per direction between Logan Street and Interstate 225. Two lanes in each direction were also added to Interstate 25 from Interstate 225 to the Colorado 470/E-470 junction, bringing this portion of highway to ten overall lanes of width. Interstate 225 saw expansion to six overall lanes between Interstate 25 and Park Road at Aurora. Eight interchanges were reconstructed, including the southern terminal of Interstate 225. The highway aspect of the project entailed $795 of the overall $1.67-billion project. To mitigate time concerns, a design-build scheme was implemented to the overall project. This allowed construction and design to take place simultaneously.

Similar projects using this form of engineering occurred with the Colorado 470/E-470 project and Interstate 15 reconstruction in Salt Lake City. Light rail lines were added along the west side of Interstate 25 and down the median of Interstate 225. A new highway lighting system was also put in place. The new fixtures use 1,000-watt lamps on 65-foot poles placed every 370 feet within the freeway median. Additionally sound barriers were also placed at certain locations within the project zone. Intelligent Transportation Systems (ITS) added during the T-REX project included ramp meters, variable message signs (VMS) and closed circuit cameras. The goal was to have the project completed on or before June 2008. Fortunately, accelerated construction resulted in a late 2006 completion date, 22 months ahead of schedule.6

The North Forty

Due to increasing development and rise in traffic volumes, expansion of Interstate 25 was slated to occur along a 40-mile stretch north of the capital city. The $370 project was broken into four phases, the first of which incurred the southernmost seven miles of the project area, covering the alignment between Colorado 7 and 52. This $73 million segment involved safety and capacity improvements. Construction ran between November 2001 and early 2005. Included in Phase One was an expansion of Interstate 25 from four to six lanes, reconstruction of the Weld County 8 interchange and removal of a railroad overpass to the north. The overall scheme allows for the addition of HOV lanes.

Phase Two entailed widening of Interstate 29 from Colorado 52 to Colorado 119. $36-million in road work on this element of the North Forty took place between November 2006 and June 2009. Phase Three widening of Interstate 25, between Colorado 119 and 66, expanded the freeway to six lanes and replaced five bridges during work from September 2007 and July 2009. Future work will widen Interstate 25 northward to Colorado 14 at Fort Collins.7

For a history of the completion of Interstate 25 in Colorado, visit Interstate 25 @ AARoads.

For a history of the completion of Interstate 25 in Wyoming, visit Interstate 25 @ AARoads.

Highway Guides

North End – Buffalo, Wyoming

I-25 US 87 North at I-90

I-25/US 87 north at US 16 - Buffalo, Wyoming

Exit 299 leaves I-25/US 87 north for US 16 and Business Loop I-90 west to Downtown Buffalo one mile ahead of the exchange with Interstate 90. Photo taken 08/12/16.

I-25 north end - Buffalo, Wyoming

An end shield for Interstate 25 north stands just east of Johnson County Fairgrounds and ahead of the directional T interchange (Exit 300) with I-90. Photo taken 08/05/16.

I-25/US 87 north at I-90 - Buffalo, Wyoming
I-25/US 87 north at I-90 - Buffalo, Wyoming
I-25/US 87 north at I-90 - Buffalo, Wyoming

Single lane ramps partition traffic for the continuation of U.S. 87 north onto I-90 west to Sheridan and Billings, Montana and I-90 east to Gillette, Moorcroft and Rapid City, South Dakota. Photos taken 08/05/16.

I-90 US 87 East at I-25

I-90/US 87 east at I-25 - Buffalo, Wyoming

Interstate 90 & U.S. 87 angle southeast across a broad valley fed by Rock Creek on the approach to Buffalo and I-25 south. Photo taken 08/07/16.

I-90/US 87 east at I-25 - Buffalo, Wyoming

Business loops for both I-25 south and I-90 east branch southward from Interstate 90 to accompany U.S. 87 Business along Main Street to U.S. 16 in Buffalo. I-25 bypasses the city center to the east. Photo taken 08/07/16.

I-90/US 87 east at I-25 - Buffalo, Wyoming

U.S. 87 splits with I-90 east at the directional T interchange (Exit 56B) for Interstate 25 south. The two overlap to Casper. Photo taken 08/07/16.

I-90 West at I-25 US 87

I-90 west at I-25/US 87 - Buffalo, Wyoming

Interstate 90 curves northwest from Business Loop I-90 and U.S. 16 to next meet the north end of I-25 at Exit 56B. Photo taken 08/07/16.

I-90 west at I-25/US 87 - Buffalo, Wyoming

A left side ramp takes motorists onto Interstate 25 & U.S. 87 south. U.S. 87 north commingles with the I-90 corridor north to Sheridan and Billings, Montana. Photo taken 08/07/16.

I-90 west at I-25/US 87 - Buffalo, Wyoming

Traffic separates from I-90 west for Interstate 25 & U.S. 87 south to nearby Buffalo, Casper and Cheyenne. Business Loop I-90 west returns to I-90 at an adjacent half diamond interchange (Exit 56A on I-90 east). Photo taken 08/07/16.

I-25 North End Throwback

I-25 north at I-90 in March 2001. Photos by Dale Sanderson.

I-25 north at I-90 - Buffalo, WY - 2014
I-25 north at I-90 - Buffalo, WY - 2014

Signs for Interstate 25 northbound to I-90 in Buffalo were replaced to use Clearview font in 2015. Photos taken 08/15/14.

South End – Las Cruces, New Mexico

I-25 South at I-10 US 180

I-25 south - Las Cruces, New Mexico

Entering the Las Cruces area along Interstate 25, seven miles ahead of I-10. Photo taken 04/25/17.

I-25 south at I-10 - Las Cruces, New Mexico

The final reassurance marker for Interstate 25 precedes the Wells Street underpass by New Mexico State University in Las Cruces. Photo taken 04/25/17.

I-25 south at I-10 - Las Cruces, New Mexico

Traffic separates at the south end of Interstate 25 for I-10 east toward El Paso, Texas and west to Deming, Lordsburg, and southeastern Arizona. Photo taken 04/25/17.

I-25 south at I-10 - Las Cruces, New Mexico

Traffic separates at the south end of Interstate 25 for I-10 east toward El Paso, Texas and west to Deming, Lordsburg, and southeastern Arizona. Photo taken 04/25/17.

I-10 US 180 East at I-25

I-10 east at I-25 - Las Cruces, New Mexico

I-10/U.S. 180 travel southeast past Downtown Las Cruces and converge with the end of Interstate 25 beyond New Mexico State University. Photo taken 04/25/17.

I-10 east at I-25 - Las Cruces, New Mexico

Underway from April 26, 2012 to April 9, 2013, the I-10/I-25 Interchange Reconstruction Project replaced a substandard loop ramp for I-25 north with a high speed flyover.8 Photo taken 04/25/17.

I-10 east at I-25 - Las Cruces, New Mexico

The flyover ramp (Exit 144) for I-25 north to New Mexico State University and the east side of Las Cruces parts ways with Interstate 10/US 180 eastbound. Photo taken 04/25/17.

I-10 US 180 West at I-25

I-10 west at I-25 - Las Cruces, New MexicoI-10 west at I-25 - Las Cruces, New Mexico

Interstate 10, U.S. 85 and U.S. 180 leave an agricultural area across Fillmore Arroyo just ahead of the three-wye interchange (Exit 144) with Interstate 25 north. Photos taken 04/25/17.

I-10 west at I-25 - Las Cruces, New Mexico

Interstate 10 & U.S. 180 turn westward across south Las Cruces, overtaking U.S. 70 en route to Deming. I-25 lines the U.S. 85 corridor northward along the Rio Grande toward Truth or Consequences, Socorro and Albuquerque. Photo taken 04/25/17.

I-25 South End Throwback

Photos taken by Jeff Royston (12/00, 05/27/04 and 05/27/04).


  1. U.S. and Interstate Highways in New Mexico (Steve Riner).
  2. Big I Project Information New Mexico State Highway & Transportation Department.
  3. “World Premiere” Albuquerque Tribune, The (NM), May 24, 2002.
  4. “Twin Mountain to Start Road Work” Albuquerque Journal (NM), February 17, 2000.
  5. “Project Was A Boon To City’s Economy.” Albuquerque Journal (NM), May 26, 2002.
  6. T-REX CDOT.
  7. The North Forty Project. CDOT.
  8. “I-10/I-25 interchange project to finish ahead of scheduled.” Las Cruces Sun-News (NM), March 30, 2013.

Page updated June 11, 2019.