Interstate 25

Joining the capital cities of Santa Fe, Denver and Cheyenne, Interstate 25 follows the Front Range of the Rocky Mountains. I-25 also serves Albuquerque, New Mexico’s largest city and Pueblo and Colorado Springs in central Colorado. Suburban growth along the corridor nearly joins the Denver and Colorado Springs metropolitan areas.

High Occupancy Toll (HO/T) lanes (North I-25 Express Lanes) accompany Interstate 25 from 20th Street at Downtown Denver to Adams County, north of I-270 and south of Thornton. The I-25 North Express Lanes: Mead to Fort Collins project extends the managed lanes northward to SH 14 (Mulberry Street) at Exit 269 in northeast Fort Collins. Costing $302 million, construction commenced in 2018 on I-25 between Sh 402 and Mulberry, and from SH 56 to SH 402 in late 2019. Work runs through 2023.

The I-25 South Gap Project Monument upgraded 18 miles of Interstate 25 from south of Castle Rock to Monument. Partitioned into three sections, $419 million in construction through November 2022 expanded I-25 with tolled Express Lanes from SH 105 (2nd Street) / Exit 161 to a point south of Exit 181 / Plum Creek Parkway. Work commenced in September 2018 and the Express Lanes opened on December 10, 2021.

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

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 cosigned 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 ran from Socorro to Belen. Overall upgrades to U.S. 85 for I-25 were completed through the state in 1980.¹

Construction building I-25 in Colorado ran from 1958 to 1969. A timeline for the completion in the Centennial State is on the Interstate 25 Colorado guide on AARoads.

Interstate 25 in Wyoming was constructed from 1958 to 1982. More detailed information is on the Interstate 25 Wyoming guide on AARoads.

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 N Nevada Avenue (former Business Loop I-25) and Rockrimmon, and from Woodmen to North Academy. Completion of Colorado Springs Metropolitan Interstate Expansion (COSMIX) occurred by December 2007.

T-REX

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 Platte Valley Drive Road. Encompassing 11.2 miles, the $33 million project broke ground on November 16, 1948. The road eventually became known as the Valley Highway.

Valley Highway opened between Evans Avenue and 52nd Avenue 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 I-70 and I-25 on July 21, 1976. Both facilities were well over capacity with Valley Highway at 230,000 vpd and I-225 at 120,000 vpd in 1998. Traffic volumes were consistent in both directions of travel because of Denver’s two major employment hubs: the Central Business District to the north and the Southeast Business District to the south.

Involving the corridors along both I-25 and I-225, T-REX was the acronym for Transportation Expansion Project. Studies began in 1992 on how to address the burgeoning transportation woes along Valley Highway. As a result, a partnership formed between 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).

Several options were in consideration by 1995. They included the construction of new freeway lanes, the double decking of existing freeway lanes, the construction of heavy rail, construction of monorail, and various other mass transit related options. The Denver Regional Council of Governments (DRCOG) adopted the MIS recommendations by 1997. 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 the addition of HOV lanes among other recommendations. 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