Colorado Highways: Interstate 25

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Location: South Front Range > Metro Denver > North Front Range
Length*: 298.87mi
S End: New Mexico border at Raton Pass (link to Steve Riner's site)
N End: Wyoming border north of Wellington (link to Andy Field's site)
Nationally: S End: Jct I-10 at Las Cruces, New Mexico; N End: Jct I-90 at Buffalo, Wyoming (1059mi)

Counties: Las Animas, Huerfano, Pueblo, El Paso, Dougals, Arapahoe, Denver, Adams, Broomfield, Weld, Larimer
Places: Trinidad, Walsenburg, Pueblo, Fountain, Colorado Springs, Monument, Castle Rock, Castle Pines North, Lone Tree, Centennial, Greenwood Village, Denver, Northglenn, Thornton, Broomfield, Mead, Loveland, Windsor, Fort Collins, Wellington

NHS: All Interstate Highways are by default part of the NHS. 

Freeway: Entire length (exit lists)

Business Routes:

Roadways Names:

Memorial Designations:
Scenic & Historic Byways: Santa Fe Trail (New Mexico border to Trinidad) America's Byways

Milepost Guide:

  • 0.00: New Mexico border (begin I-25 in Las Animas County)
  • 13.60: SH 12 interchange, Trinidad
  • 14.85: US 160/To US 350/To SH 239/Goddard Ave interchange
  • 34.09: BS I-25 interchange, Aguilar
  • 39.10: Enter Huerfano County
  • 49.00: BL I-25 interchange, south Walsenburg
  • 50.05: US 160/SH 10 interchange
  • 52.32: BL I-25 interchange, north Walsenburg
  • 68.85: Enter Pueblo County
  • 74.36: SH 165 interchange, Colorado City
  • 94.76: SH 45/Pueblo Blvd interchange, Pueblo
  • 97.91: BR US 50/Santa Fe Ave interchange
  • 99.95: US 50 East interchange
  • 101.38: US 50 West/SH 47 interchange
  • 116.43: Enter El Paso County
  • 127.86: US 85 interchange, Fountain
  • 131.65: SH 16 interchange, Fountain
  • 138.97: US 24 East interchange, Colorado Springs
  • 139.74: SH 115/Nevada Ave interchange
  • 141.13: US 24 West/Cimmaron St interchange
  • 160.76: SH 105 interchange, Monument
  • 163.32: Enter Douglas County, Monument Hill
  • 184.21: US 85/Founders Pkwy/Meadows Pkwy interchange, Castle Rock
  • 194.31: SH 470/E-470 interchange, Lone Tree
  • 195.13: Enter Arapahoe County
  • 197.18: SH 88 East/Arapahoe Rd interchange, Greenwood Village
  • 199.38: SH 88 West/Belleview Ave interchange, Enter Denver County
  • 200.09: I-225 interchange
  • 201.57: US 285/SH 30/Hampden Ave interchange
  • 204.03: SH 2/Colorado Blvd interchange
  • 207.48: US 85/Santa Fe Dr interchange
  • 207.99: SH 26/Alameda Ave interchange
  • 209.21: US 6/6th Ave interchange
  • 210.31: BL I-70/US 40/US 287/Colfax Ave interchange
  • 213.62: I-70 Exit 274 interchange
  • 214.46: Enter Adams County
  • 215.24: SH 53/58th Ave interchange
  • 216.30: I-76 Exit 5 interchange
  • 217.00: US 36/I-270 Exit 0 interchange
  • 223.04: SH 128/120th Ave interchange, Northglenn
  • 227.34: Enter Broomfield County
  • 227.74: E-470/Northwest Pkwy Exit 46 interchange
  • 228.02: Enter Adams County
  • 229.10: SH 7 interchange, Enter Broomfield County
  • 231.09: Enter Weld County
  • 235.11: SH 52 interchange
  • 240.11: SH 119 interchange, Longmont
  • 243.14: SH 66 interchange
  • 250.24: SH 56 interchange, Berthoud
  • 252.26: SH 60 East interchange, Johnstown
  • 253.19: Enter Larimer County
  • 255.27: SH 402 interchange
  • 257.30: US 34 interchange, Loveland
  • 262.29: SH 392 interchange, Windsor
  • 269.37: SH 14 interchange
  • 277.88: SH 1 interchange, Wellington
  • 291.97: Enter Weld County
  • 298.87: Wyoming border

Annual Average Daily Traffic (2004):

  • 8500 at New Mexico border
  • 14,900 south of Main St, Trinidad
  • 8600 north of BS 25, Aguilar
  • 7500 north of US 160/SH 10, Walsenburg
  • 12,500 north of Walsenburg BL 25
  • 16,800 north of SH 165, Colorado City
  • 34,100 north of SH 45, Pueblo
  • 60,300 north of Abriendo Ave.
  • 71,200 north of 13th St.
  • 28,200 north of US 50/SH 47
  • 27,400 north of Eden
  • 37,400 north of US 85, Fountain
  • 61,900 north of Academy Blvd., south Colorado Springs
  • 83,300 north of south Nevada Ave.
  • 94,200 north of Bijou St.
  • 103,000 north of north Fillmore St
  • 70,100 north of Briargate Pkwy.
  • 53,600 north of SH 105, Monument
  • 52,200 south of Greenland
  • 55,500 south of Wilcox St./Plum Creek Pkwy., Castle Rock
  • 91,600 north of US 85/Founders Pkwy.
  • 86,500 north of Castle Pines Pkwy.
  • 173,000 north of County Line Rd, Centennial
  • 222,000 north of Orchard Rd, Greenwood Village
  • 193,000 north of US 285/SH 30/Hampden Ave., Denver
  • 169,000 north of Downing St
  • 221,000 north of SH 26/Alameda Ave
  • 203,000 north of US 40-287/Colfax Ave.
  • 254,000 north of Park Avenue West *
  • 191,000 north of I-70
  • 234,000 between I-76 and US 36
  • 149,000 north of Thornton Pkwy., Thornton
  • 87,600 north of SH 128/120th Ave.
  • 67,500 north of SH 52
  • 61,400 north of SH 66, Longmont
  • 60,800 north of SH 56
  • 69,800 north of US 34, Loveland
  • 49,600 north of Harmony Rd., Fort Collins
  • 36,700 north of SH 14
  • 18,200 north of SH 1, Wellington
  • 17,000 at Wyoming border

* The busiest stretch of highway in Colorado

I-25 starts off in Colorado just north of Raton Pass, descending down Raton Creek Canyon toward Trinidad. I-25 passes right through the middle of town, using an elevated viaduct over streets and railroad tracks. US 160 joins I-25 at Exit 15 on the north edge of town. North from Trinidad, I-25 generally follows the eastern edge of the mountains and foothills, bypassing to the east of Augilar and Walsenburg. Walsenburg features a marked business loop, and US 160 breaks off to head west. As it continues north toward Colorado City, the terrain gets more rolling, but then flattens out again south of Pueblo.

I-25 flies right through the middle of Pueblo, rather than bypassing it.  The strecth south of downtown in the Abriendo Ave. area has a bunch of substandard features, including 50mph curves, bridges with no shoulders, 25mph exits, short accel/decel lanes, etc. At the Indiana Ave. exit I-25 passes the Rocky Mountain Steel Mill. North of downtown at Exit 101, US 50 West/SH 47, I-25 encouters its first SPUI.

North of Pueblo, I-25 picks up Fountain Creek and follows that north along the west sides of Fountain and Security-Widefield toward Colorado Springs. It is also along the east border of Fort Carson. As I-25 comes into Colorado Springs, it generally follows along the west side of Fountain Creek, swinging around the west side of downtown, then hugging the hillside that marks the west side of the Monument Creek valley through the northwest side of town. I-25 has six lanes through Colorado Springs from Circle Drive in the south to North Academy Blvd in the north. It features two elongated diamond interchanges, one at South Nevada/Tejon, the other at North Nevada/Rockrimmon/Corporate.

I-25 follows the broad Monument Valley from Colorado Springs north to Monument, and forms the east border of the Air Force Academy part of the way. Monument is basically being assimilated into the Colorado Springs metro area. North of Monument at County Line Road, I-25 rises up and crests Monument Hill, sometimes referred to as the Palmer Divide. At an elevation of 7352 feet, it is prone to severe winter weather. As a result, CDOT has continuous lighting along a three or so mile stretch of it, very rare in a rural area. At first I didn't know what the lighting was for, but Mike Ramsey dropped me a line clearing things up.

I-25 then goes through rolling terrain past Greenland and Larkspur, and after a long straight stretch along East Plum Creek arrives in Castle Rock. I-25 passes to the west of the main part of town, but the town has spread out to envelop both sides of the freeway. Castle Rock is also where the pressure of traffic from metro Denver starts to be felt. I-25 picks up a third lane each direction at the Wolfensberger Rd interchange. From Castle Rock north to Lincoln Avenue (Exit 193), I-25 climbs and falls over a very hilly portion of Douglas County, eventually coming to Lone Tree.

At Lincoln Avenue, I-25 enters the more developed portion of metro Denver. The highway has five lanes in each direction from Lincoln up to I-225 (Exit 200). Near Orchard Road and Belleview Avenue, I-25 skirts the west side of the Denver Tech Center, a massive office park that chokes I-25 and surrounding roads each rush hour. From I-225 northward I-25 has four lanes in each direction.

The section from I-225 to Santa Fe Drive used to be a substandard, with the worst section in a part called the Narrows, from University Blvd to Logan St (MP 205-206). This area hadn't seen a significant upgrade since it was built in the '50s and it was showing. There was poor drainage and minimal shoulders, and the underpass at Logan St would flood during heavy rains, twice in fact during the summer of 1998. It received the nickname Lake Logan. The underpass at Evans Av also had a habit of flooding. But the Southeast Corridor Project, later renamed to T-REX (Transportation Expasion Project) remedied many things in the area. The $1.6 billion project, from Summer 2001 to Fall 2006, expanded I-25 to four lanes in each direction (up from three) from Broadway to I-225, and five lanes from I-225 to C-470 (up from three). The Regional Transportation District at the same time built its Southeast Line along I-25's west side from the existing Broadway station southeast to Lincoln Avenue. Interchange, bridge, ITS, and drainage improvements were made. The left exit and left entrance at the I-225 interchange were eliminated. The project was possible thanks to state voters in November 1999 approving TRANs and metro RTD residents approving bonding for the light rail. A seperate project that ran almost concurrently was rebuilding the I-25 viaduct over Broadway, which at one time was rated as one of the worst bridges in the state.

From Santa Fe northward, I-25 has four lanes in each direction and stays within earshot of the South Platte River until north of Speer Blvd. The section from 6th Avenue (Exit 209) to 20th Street (Exit 212C) has, I feel, too many closely spaced entrances and exits, as well as a sharp curve going over the South Platte River next to Invesco Field at Mile High.

Five miles from 20th Street to north of US 36 have reversible HOT lanes (high occupancy or toll) in the median, two lanes wide Vehicles with two or more people, motorcycles and alternative fuel vehicles (electric, ethonal, propane) are allowed to use the lanes for free, while single occupant vehicles can use them via an electronic toll. The toll point is just south of 58th Ave with HOVs directed into the west lane and toll vehicles into the east lane where the overhead toll reader is. Toll payers need an ExpressToll account, the same eletronic collection system first used by E-470. The lanes are controlled with changeable message signs and gates, with flow going southbound in the morning and northbound evening and weekends. For northbound traffic, entry points are 1) I-25 near 20th St and 2) 20th St downtown with exit points to 1) 70th Ave, 2) westbound US 36 and 3) northbound I-25 north of US 36.  For southbound traffic entry points are 1) I-25 north of US 36, 2) 70th Ave and 3) eastbound US 36 near Pecos with exit points to 1) southbound I-25 near Speer and 2) 19th St downtown. The toll for single occupant vehicles depends on the time of day, but is highest during peak hours. The idea to make the toll high enough so that the lanes don't get so much traffic that HOVs are delayed.

The interchange with I-70 (Exit 214) is known as the Mousetrap, and is much better off now than it used to be. See the History section below for more. From the Mousetrap up to the Turnpike Tangle, I-25 has four lanes with auxiliary lanes going each direction, and a nice broad concrete cross section. The Turnpike Tangle is my name for the mass of ramps and bridges that make up I-25's two interchanges with I-76 (Exit 216) and I-270/US 36 (Exit 217), along with the I-76/270 interchange. Construction was ongoing from the mid-'90s to 2008, with the goals of extending I-270 from 76 northwest to 25/36, and connecting HOV lanes on 25 and 36 with direct ramps. See my I-270 and US 36 listings for more.

From the Turnpike Tangle north and out of the metro, I-25 has three lanes in each direction. At 104th Avenue, the speed limit goes from 55 to 65, and at SH 128/120th Avenue (Exit 223), a good chunk of the traffic melts away. From 120th up past Wellington, I-25 is mostly straight and flat, with the steepest grade being just south of SH 56/Berthoud (Exit 250). At SH 66 (Exit 243) the three lanes in each direction become two, and it is like that all the way to Wyoming. From SH 7 to Wellington, there are exits, on average, about every three miles, so you keep busy avoiding exiting/entering cars. Traffic levels drop very suddenly at Fort Collins. Heading north, when you hit the Buckeye Road exit (Exit 281), the land suddenly changes from lush, green farmland to brown prairie. Ah, the wonders of irrigation.....

I-25 is the main artery of the North Front Range for traffic between Denver and Fort Collins. There has been an ongoing North Front Range Transportation Alternatives Feasibility Study to determine the best thing to do in the corridor, which could be one or a combination of passenger rail service, intercity bus service, HOV lanes, or more general lanes. Some numbers: There were 88 accidents in the 14-mile stretch from SH 7 to SH 66 in 1992, but that ballooned to 183 in 1996. The scariest part is that traffic counts keep increasing. Planners expect the counts to increase by (not to) 600,000 motorists between Loveland and Denver by 2020. Some call it "a looming transportation nightmare." (April 13, 1998 Fort Collins Coloradoan by the AP) Interchange improvement projects completed since the late '90s include Exit 240 (SH 119) at Longmont, Exit 268 (SH 68) at Fort Collins, Exit 235 (SH 52) at Dacono and Exit 257 (US 34) at Loveland.

Photo Gallery:

Before I-25 was constructed, US 87 pretty much exactly followed its alignment. As a consequence, US 87 is not signed and basically nonexistent. Outside of Denver, the freeway that would become I-25 started as scattered expressway and freeway sections of US 85-87 and US 87-SH 185. See those listings for more. I-25 first appears on state maps in 1961.

Years when various sections of I-25 are shown as completed on maps (south to north):

New Mexico border to Wootton
Wootton to Spring Creek
Spring Creek into Trinidad
A couple of interchanges in place by 1962
Freeway 1969
Trinidad to Ludlow
Ludlow to south Walsenburg
A couple of interchanges in place by 1962
Freeway 1970
Walsenburg bypass
North Walsenburg to Apache City
Apache City to SH 165
SH 165 to south of Pueblo
South of Pueblo to 13th St
13th St to US 50 east
US 85-87 freeway before 1957
US 50 east to north of Pueblo
US 85-87 expressway before 1957
Freeway 1962
North of Pueblo to Fountain
US 85-87 expressway 1958
Freeway 1960
Fountain to South Nevada Ave
US 85-87 expressway 1957
Freeway 1960
South Nevada Ave to Mesa Rd
Mesa Rd to North Nevada Ave
North Nevada Ave to Monument
US 85-87 expressway before 1957
Freeway 1960
Monument to Larkspur
US 85-87 expressway before 1957
Freeway 1965
Larkspur to south Castle Rock
US 85-87 expressway before 1957
Freeway 1968
Castle Rock bypass
US 85-87 expressway before 1957
Freeway 1965
North Castle Rock to about Lincoln Ave
US 87 expressway before 1957
Freeway by 1960
Lincoln Ave to about Arapahoe Rd
US 87 expressway 1958
Freeway by 1960
Arapahoe Rd to Colorado Blvd
Colorado Blvd to Emerson St
Emerson St to 3rd Ave
3rd Ave to Colfax Ave
Colfax Ave to 38th Ave
38th Ave to 58th Ave
58th Ave to 120th Ave
US 87 expressway before 1957
Freeway 1962
120th Ave to SH 7
US 87 expressway before 1957
Freeway 1963
SH 7 to SH 52
SH 52 to SH 66
SH 66 to SH 56
SH 56 to US 34
US 34 to Timnath
Timnath to SH 14
SH 14 to north of Wellington
North of Wellington to Wyoming border

From Castle Rock to Denver, numerous projects have been done starting in the late 1990s. The Founders/Meadows interchange (Exit 184) was rebuilt in 1998, and the former US 85 partial interchange south of Founders was removed in November 2001. Two major projects to widen the accident-prone stretch from Founders to Lincoln to six lanes were completed in 2002.  Widening to six lanes from Founders to Wolfensberger was completed in November 2007. The substandard Exit 191 (Schweiger) and Surrey Ridge (Exit 189) interchanges, which featured ramps that teed into mainline I-25 like a right-in-right-out intersection, were closed September 4, 2009 when the new east frontage road was opened. A project to complete four lanes each direction from RidgeGate to Founders was complete in October 2009, while three lanes each direction from Wolfensberger to south of Plum Creek Pkwy was completed in December 2009. Also in December 2009, the new Plum Creek Pkwy interchange in south Castle Rock opened. Previously it featured a split arrangement with the southbound ramps intersecting Plum Creek Pkwy and the northbound ramps intersecting Wilcox St, but the interchange was realigned entirely along Plum Creek Pkwy.
In Denver, a major project to upgrade the Broadway viaduct was completed in spring 2006. The viaduct, built in 1958, was one of the worst-rated bridges on the state highway system and the project expanded I-25 in the area to four lanes in each direction, up from three.

The north I-25 HOT lanes were converted from HOV-only to HOT operation on June 2, 2006. The lanes had been HOV-only since their opening in 1994. The HOT conversion was in response to a law passed in 1999 requiring the tolling.

The Southeast Corridor Project, called the T-REX Project (TRansportation EXpansion), started on September 24, 2001. The project involved major reconstruction of I-25 from Broadway in Denver to Lincoln Ave in Lone Tree. Every bridge from Logan St to I-225, excluding Yale Ave, was rebuilt. Drainage improvements were made to eliminate "Lake Logan", substandard ramps and accel/decel lanes were reconstructed, the University cloverleaf was modified to a SPUI, the left entrance/exit at I-225 was eliminated, and ITS elements were added. A double track light-rail line was built along I-25's west side, with new light rail stations, park-n-ride lots and pedestrian overpasses in the Tech Center. Through lanes were added to bring the number to four in each direction from Broadway to I-225 and five in each direction from I-225 to SH 470. Roadway improvements were completed August 22, 2006 and the light rail line opened November 17, 2006.

Between US 36 and SH 7 numerous projects have happened on I-25 since the late 1990s. A new overpass near 112th Ave was built in 2003. The 120th Ave bridge was replaced in 2006. The 128th Ave bridge was replaced in 2008. New interchanges at 136th Ave and 144th Ave opened in 2004 and 2006, respectively. The replacement of 104th Ave bridge was completed in 2010.

The six-lane widening north of metro Denver, known as the North 40 Project (40 miles from SH 7 to SH 14) had its first competion in fall 2004 of the widening from SH 7 to SH 52. Two separate projects, completed in April 2009, extended the six lanes north to SH 66. In fall 2012 a project rebuilding the SH 392 interchange with a higher-capacity diamond interchange was complete.

The US 34 interchange at Loveland was originally a full cloverleaf. This led to white-knuckle experiences for drivers using the loop ramps, as they were only going 20 mph and mixing with 75 mph I-25 traffic in the weave area. In summer 2010 the northeast and southwest loops were removed and replaced with intersections on US 34 as part of a safety project entirely funded by the Centerra development.

In Colorado Springs, the project known as COSMIX (Colorado Springs Metro Interstate Expansion) was completed in December 2007. The project was a design-build project modeled after T-REX. COSMIX accomplsihed: Total rebuild of the Bijou Street interchange, total rebuild of the Nevada/Rockrimmon interchanges and widening from Fillmore to North Academy. At the completion of COSMIX, I-25 had six lanes all the way through Colorado Springs from Circle Drive to North Academy; previously it was four lanes through the Bijou interchange and north of Fillmore. Among the deficiencies corrected by COSMIX were chronic flooding at the Bijou underpass, sharp ramps at the Rockrimmon interchange and a left exit southbound at North Nevada.

COSMIX was the feather in the cap for I-25 in Colorado Springs, it came on the heels of numerous smaller projects:
Another area where I-25 has required a total rebuild is through the central part of Trinidad, a large portion of which is elevated viaduct. The project to replace the northbound viaduct was completed in later 2009, and with American Recovery and Reinvestment Act (federal stimulus) the southbound viaduct was added to the contract and work swithced over to that side. The southbound viaduct was opened in February 2011.

The Valley Highway: What was originally built in Denver was not I-25, but the Valley Highway. It was completed in sections from north to south. All 11mi of the entire route (from 58th Ave. to Evans Ave.) opened for traffic on November 23, 1958. It was only built to four lanes, and traffic quickly reached capacity. Contingencies were built into the right-of-way for six lanes, but CDH could not afford to build all six. Funding would have come from the Interstate system for it, since the Valley Highway would eventually be I-25, but the funding was not available until 1957, too soon to be used for the Valley Highway.

The Mousetrap: The Mousetrap is what the I-25-70 interchange in north Denver is called. The original Mousetrap was an interchange on the Valley Highway, not designed or built to ever be an Interstate. It opened in 1951 when the first 2.2-mile section of the Valley Highway opened from 38th to 52nd Avenues. The Mousetrap was the interchange with 46th Avenue, at the time a major east-west street. The Mousetrap cost $2.2M, the largest contract ever awarded by CDH.

In the 1960s, I-70 was slated to be extended across Colorado, rather than just ending in Denver, so I-70 opened in 1964 as an elevated highway over 46th Avenue. The old Valley Highway interchange at 46th then became the link between I-25 and I-70. It still had substandard ramps and curves, and accidents were "common". The Mousetrap name dates from the late 1960s when airborne traffic reporter Don Martin observed the intertwining ramps could trap a mouse. In 1993 Martin remarked, "It had a terrible curve so that eastbound trucks going from I-25 to I-70 were always rolling over. They were the mice."

In 1971 the Denver Police Department built a 60-foot observation tower in the middle of the Mousetrap to watch for accidents and monitor traffic conditions. The substandard Mousetrap remained for over 20 years, when in 1984 it snagged its ultimate victim: Before dawn on August 1, 1984, a truck carrying six armed Navy torpedoes overturned on the SB-EB ramp. Both freeways were closed for eight hours so the torpedoes could be cleared, resulting in a traffic nightmare. The accident became a national news event and made Congress aware of Denver's problems with the Mousetrap. It was the pivotal event in starting reconstruction of the Mousetrap. At the time, the interchange carried 300,000 vehicles a day; 1997's count was 340,000 VPD, more than projected to use it in 2010.

Construction on rebuilding the Mousetrap started in June 1987. Many phases followed, including: New 44th Avenue bridge; new I-25 alignment through interchange; new I-70 alignment through interchange; widen I-25 from 38th to 58th Avenues and new HOV lanes; reconstruct 58th interchange; reconstruct 38th/Park interchange including huge flyover into downtown; rebuild I-70 from I-25 to Washington; and rebuild I-70 from Washington to Brighton. $269M later, the reconstruction was finished with a dedication of the westbound I-70 viaduct on December 16, 2003.
Info from articles in the March 23, 1998 and December 16, 2003 Rocky Mountain News

The Mousetrap in 1958, looking north.

Looking south along I-25 over the Mousetrap in 1998. HOV lanes go down the middle. Both graphics are from the March 23, 1998 Rocky Mountain News.

Related Site: I-25 @ Interstate Guide


Last updated 8 November 2014