Find Colorado Interstates and Federal Highways
History of Interstates and U.S. Highways in Colorado
Colorado’s Interstate and U.S. highway system has been crucial to connecting the Rocky Mountain state to the rest of the country. The state’s early highways were constructed in the 1910s and 1920s, with major U.S. routes such as U.S. 40 and U.S. 50 playing key roles in connecting Colorado to the east and west coasts. The establishment of the Interstate Highway System in the 1950s brought the construction of I-25, I-70, and I-76, which serve as the major arteries of transportation in the state today.
Colorado’s highways are essential for both tourism and commerce, as the state sees heavy traffic from visitors to ski resorts and national parks, as well as the transportation of goods through major routes like I-70. Interstate 70, which passes through the heart of the Rocky Mountains, sees heavy traffic year-round, with some sections seeing over 50,000 vehicles per day during peak seasons. In addition to supporting the state’s economy, Colorado’s highways are vital for regional and cross-country travel, particularly for freight transportation.
Ongoing highway projects in Colorado aim to accommodate population growth and reduce traffic congestion. The expansion of I-25, particularly around Denver and Colorado Springs, is a major focus, along with improvements to I-70’s mountain corridor. The state is also planning new highway infrastructure, such as additional lanes and interchanges, to address the growing demands on the transportation network.
Building I-70 Through the Rockies: The Eisenhower Tunnel
No highway project in Colorado tested engineers and workers more than driving Interstate 70 through the heart of the Rocky Mountains. The centerpiece of that effort — and arguably the most difficult single construction project in the history of the U.S. Interstate system — was the Eisenhower–Edwin C. Johnson Memorial Tunnel, completed in two bores between 1973 and 1979. At 11,158 feet above sea level, it remains the highest vehicular tunnel on any Interstate highway in the country.
Before the tunnel, I-70 traffic crossed Loveland Pass at over 11,900 feet — a winding, treacherous route that shut down regularly in winter. The tunnel was meant to solve that, but building it introduced its own extraordinary challenges. Workers bored through some of the most fractured, unpredictable rock in the Rockies: granite, schist, and gneiss that shifted pressure unexpectedly, causing cave-ins and forcing constant reinforcement. High-altitude conditions thinned the air enough that equipment ran less efficiently and workers fatigued faster, requiring crews to rotate more frequently than at lower elevations.
Avalanche risk was a constant threat during construction and remains a defining feature of the I-70 mountain corridor today. The terrain on both approaches to the tunnel sits directly in avalanche paths, requiring CDOT to conduct controlled avalanche blasts to protect the roadway every winter. Entire sections of I-70 can close within minutes when slide conditions develop, and the highway's mountain segment between Denver and Vail is routinely ranked as one of the most dangerous winter driving corridors in the country. The combination of steep grades, tight curves, 11,000-foot elevation, and sudden weather changes has made this stretch a perpetual maintenance and safety challenge since the day it opened.
US-550 — The Million Dollar Highway
Running through the San Juan Mountains of southwestern Colorado, U.S. 550 between Ouray and Silverton is one of the most celebrated — and most unforgiving — stretches of road in the United States. Known as the Million Dollar Highway, the name itself is disputed: some say it refers to the cost of early construction, others to the gold ore embedded in the road fill, and still others simply to the views. What isn't disputed is how hard it was to build, and how dangerous it remains to drive.
The road clings to cliff faces above thousand-foot drops, passing through multiple switchbacks that exceed 11,000 feet in elevation. There are no guardrails on much of the route — not an oversight, but a deliberate decision in some sections, because the snowplow blades that keep the road passable in winter would catch on guardrail posts and be destroyed. The tradeoff is a road where a moment of inattention can mean going off a cliff with nothing between you and the canyon floor.
Construction of this route in the early 20th century meant hand-drilling and blasting into near-vertical canyon walls with almost no access roads. Workers were lowered down cliff faces on ropes to set charges in the rock. The San Juans receive some of the heaviest snowfall in Colorado, and avalanche chutes cross the road in multiple places — the route passes directly through active slide paths that still bury the highway several times each winter. Despite repeated proposals to add more protective infrastructure, the terrain simply doesn't allow for it in many places: there is no room between the mountain wall and the drop.
US-550 through the San Juans stands as proof that some roads don't get easier just because they've been paved — the mountain dictates the terms, and drivers and engineers have been working around those terms for over a century.
Busiest and Longest Federal Interstates and U.S. Highways in Colorado
| Interstate or Highway | Length (mi) | Length (km) | Southern or Western Terminus | Northern or Eastern Terminus | Created |
|---|---|---|---|---|---|
| I-25 | 299 | 481 | New Mexico Border | Wyoming Border | 1956 |
| I-70 | 449 | 723 | Utah Border | Kansas Border | 1956 |
| I-76 | 187 | 301 | Denver, CO | Nebraska Border | 1958 |
| U.S. 40 | 500 | 805 | Utah Border | Kansas Border | 1926 |
| U.S. 50 | 468 | 753 | Utah Border | Kansas Border | 1926 |
| U.S. 285 | 263 | 423 | New Mexico Border | Denver, CO | 1926 |
| U.S. 287 | 300 | 483 | Texas Border | Wyoming Border | 1926 |
| U.S. 6 | 407 | 655 | Utah Border | Nebraska Border | 1926 |
| U.S. 34 | 279 | 449 | Granby, CO | Nebraska Border | 1926 |
| I-225 | 12 | 19 | Aurora, CO | Denver, CO | 1970 |
| U.S. 24 | 295 | 475 | Minturn, CO | Kansas Border | 1926 |
| U.S. 550 | 126 | 203 | New Mexico Border | Montrose, CO | 1926 |
| U.S. 36 | 233 | 375 | Denver, CO | Kansas Border | 1926 |
| U.S. 160 | 451 | 726 | Utah Border | Kansas Border | 1926 |
| U.S. 385 | 316 | 509 | New Mexico Border | Nebraska Border | 1926 |
| U.S. 287 | 298 | 480 | Texas Border | Wyoming Border | 1926 |
Colorado Designated Highways
Colorado Interstate Highway 25, I-25
Colorado Interstate Highway 25, I-25 Bus
Colorado Interstate Highway 25, I-25 N
Colorado Interstate Highway 25, I-25 S
Colorado Interstate Highway 25, Interstate 25 Spur
Colorado Interstate Highway 25, Main St
Colorado Interstate Highway 25, N Interstate 25
Colorado Interstate Highway 25, N Nevada Ave
Colorado Interstate Highway 25, S Nevada Ave
Colorado Interstate Highway 25, W Cimarron St
Colorado Interstate Highway 25, Walsen Ave
Colorado Interstate Highway 70, I 70 Business Loop
Colorado Interstate Highway 70, I-70 E
Colorado Interstate Highway 70, I-70 W
Colorado Interstate Highway 70, N 1st St
Colorado Interstate Highway 70, Pitkin Ave
Colorado Interstate Highway 70, S 1st St
Colorado Interstate Highway 70, Ute Ave
Colorado Interstate Highway 76, I-76 E
Colorado Interstate Highway 76, I-76 W
Colorado Interstate Highway 225, I-225 N
Colorado Interstate Highway 225, I-225 S
Colorado Interstate Highway 270, I-270 E
Colorado Interstate Highway 270, I-270 W
Colorado US Highway 6, Bee St
Colorado US Highway 6, Blue River Pkwy
Colorado US Highway 6, Central Ave
Colorado US Highway 6, Chestnut St
Colorado US Highway 6, E 1st St
Colorado US Highway 6, E Chestnut St
Colorado US Highway 6, E Denver St
Colorado US Highway 6, E Main St
Colorado US Highway 6, E Railroad St
Colorado US Highway 6, E Weston St
Colorado US Highway 6, F Rd
Colorado US Highway 6, Front St
Colorado US Highway 6, G Rd
Colorado US Highway 6, Grand Ave
Colorado US Highway 6, Highway 6 and 24
Colorado US Highway 6, I 70 Business Loop
Colorado US Highway 6, Main St
Colorado US Highway 6, N 3rd St
Colorado US Highway 6, N 4th St
Colorado US Highway 6, N I 76 Frontage Rd
Colorado US Highway 6, North Ave
Colorado US Highway 6, S 3rd St
Colorado US Highway 6, S 4th St
Colorado US Highway 6, S Division Ave
Colorado US Highway 6, S Front St
Colorado US Highway 6, Steele St
Colorado US Highway 6, US-6
Colorado US Highway 6, US-6 E
Colorado US Highway 6, US-6 W
Colorado US Highway 6, Vasquez Blvd
Colorado US Highway 6, W 1st St
Colorado US Highway 6, W 6th Ave
Colorado US Highway 6, W 8th St
Colorado US Highway 6, W Denver Ave
Colorado US Highway 6, W Denver St
Colorado US Highway 6, W Main St
Colorado US Highway 6, W Weston St
Colorado US Highway 24, 2nd St
Colorado US Highway 24, 4th St
Colorado US Highway 24, 5th St
Colorado US Highway 24, Caribou St
Colorado US Highway 24, E 9th St
Colorado US Highway 24, E Cimarron St
Colorado US Highway 24, E Fountain Blvd
Colorado US Highway 24, E Platte Ave
Colorado US Highway 24, E US-24
Colorado US Highway 24, Harrison Ave
Colorado US Highway 24, Main St
Colorado US Highway 24, N Poplar St
Colorado US Highway 24, N Powers Blvd
Colorado US Highway 24, N Wahsatch Ave
Colorado US Highway 24, Poplar St
Colorado US Highway 24, Powers Blvd
Colorado US Highway 24, Rose Ave
Colorado US Highway 24, S Powers Blvd
Colorado US Highway 24, S Wahsatch Ave
Colorado US Highway 24, US-24
Colorado US Highway 24, US-24 E
Colorado US Highway 24, US-24 W
Colorado US Highway 34, 8th Ave
Colorado US Highway 34, 9th St
Colorado US Highway 34, 10th St
Colorado US Highway 34, 11th Ave
Colorado US Highway 34, 18th St
Colorado US Highway 34, Big Thompson Ave
Colorado US Highway 34, Big Thompson Canyon Rd
Colorado US Highway 34, E 1st Ave
Colorado US Highway 34, E 1st St
Colorado US Highway 34, E 3rd St
Colorado US Highway 34, E 8th Ave
Colorado US Highway 34, E 18th St
Colorado US Highway 34, E Edison St
Colorado US Highway 34, E Eisenhower Blvd
Colorado US Highway 34, E Platte Ave
Colorado US Highway 34, E Wonder View Ave
Colorado US Highway 34, Edison St
Colorado US Highway 34, Fall River Rd
Colorado US Highway 34, US-34
Colorado US Highway 34, US-34 Bus
Colorado US Highway 34, W 1st Ave
Colorado US Highway 34, W 1st St
Colorado US Highway 34, W 3rd St
Colorado US Highway 34, W 8th Ave
Colorado US Highway 34, W 10th St
Colorado US Highway 34, W 28th St
Colorado US Highway 34, W Eisenhower Blvd
Colorado US Highway 34, W Elkhorn Ave
Colorado US Highway 34, W Platte Ave
Colorado US Highway 34, W Wonder View Ave
Colorado US Highway 36, 5th Ave
Colorado US Highway 36, 28th St
Colorado US Highway 36, Broadway St
Colorado US Highway 36, County Rd 6
Colorado US Highway 36, E Colfax Ave
Colorado US Highway 36, E Elkhorn Ave
Colorado US Highway 36, Foothills Hwy
Colorado US Highway 36, Main St
Colorado US Highway 36, Moraine Ave
Colorado US Highway 36, N Foothills Hwy
Colorado US Highway 36, N Main St
Colorado US Highway 36, N Saint Vrain Ave
Colorado US Highway 36, N Saint Vrain Dr
Colorado US Highway 36, Saint Vrain Ave
Colorado US Highway 36, US-36
Colorado US Highway 36, US-36 E
Colorado US Highway 36, US-36 W
Colorado US Highway 36, Ute Hwy
Colorado US Highway 36, W Colfax Ave
Colorado US Highway 36, W Main St
Colorado US Highway 40, E 4th St
Colorado US Highway 40, E Agate Ave
Colorado US Highway 40, E Brontosaurus Blvd
Colorado US Highway 40, E Jefferson Ave
Colorado US Highway 40, E Park Ave
Colorado US Highway 40, E Victory Way
Colorado US Highway 40, Evergreen Pkwy
Colorado US Highway 40, Genesee Mountain Rd
Colorado US Highway 40, Lincoln Ave
Colorado US Highway 40, Lincoln St
Colorado US Highway 40, Park Ave
Colorado US Highway 40, S Lincoln Ave
Colorado US Highway 40, US-40
Colorado US Highway 40, W 4th St
Colorado US Highway 40, W Agate Ave
Colorado US Highway 40, W Brontosaurus Blvd
Colorado US Highway 40, W Byers Ave
Colorado US Highway 40, W Colfax Ave
Colorado US Highway 40, W Jefferson Ave
Colorado US Highway 40, W Jefferson St
Colorado US Highway 40, W Park Ave
Colorado US Highway 40, W Victory Way
Colorado US Highway 40, Zerex
Colorado US Highway 50, 1st St
Colorado US Highway 50, Amb Thompson Blvd
Colorado US Highway 50, Bent Ave
Colorado US Highway 50, E 1st St
Colorado US Highway 50, E Bowker Ave
Colorado US Highway 50, E Cranston Ave
Colorado US Highway 50, E Main St
Colorado US Highway 50, E Rainbow Blvd
Colorado US Highway 50, E Tomichi Ave
Colorado US Highway 50, Elm Ave
Colorado US Highway 50, Main St
Colorado US Highway 50, N Bent Ave
Colorado US Highway 50, N Main St
Colorado US Highway 50, N San Juan Ave
Colorado US Highway 50, N Townsend Ave
Colorado US Highway 50, Royal Gorge Blvd
Colorado US Highway 50, S 5th St
Colorado US Highway 50, S Main St
Colorado US Highway 50, S Santa Fe Ave
Colorado US Highway 50, S Townsend Ave
Colorado US Highway 50, Santa Fe Dr
Colorado US Highway 50, Swink Ave
Colorado US Highway 50, US-50
Colorado US Highway 50, US-50 Bus
Colorado US Highway 50, W 1st St
Colorado US Highway 50, W Bowker Ave
Colorado US Highway 50, W Cranston Ave
Colorado US Highway 50, W Rainbow Blvd
Colorado US Highway 50, W Tomichi Ave
Colorado US Highway 84, US-84
Colorado US Highway 85, 8th Ave
Colorado US Highway 85, Denver Ave
Colorado US Highway 85, E 160th Ave
Colorado US Highway 85, E Bridge St
Colorado US Highway 85, E Las Vegas St
Colorado US Highway 85, Founders Pkwy
Colorado US Highway 85, Lake Ave
Colorado US Highway 85, Main St
Colorado US Highway 85, Meadows Pkwy
Colorado US Highway 85, N 2nd St
Colorado US Highway 85, N 8th Ave
Colorado US Highway 85, N Main St
Colorado US Highway 85, N Santa Fe Ave
Colorado US Highway 85, Oak Ave
Colorado US Highway 85, S 2nd St
Colorado US Highway 85, S Denver Ave
Colorado US Highway 85, S Kalamath St
Colorado US Highway 85, S Nevada Ave
Colorado US Highway 85, S Oak Ave
Colorado US Highway 85, S Platte River Dr
Colorado US Highway 85, S Santa Fe Ave
Colorado US Highway 85, S Santa Fe Dr
Colorado US Highway 85, US-85
Colorado US Highway 85, US-85 Bus
Colorado US Highway 85, Venetucci Blvd
Colorado US Highway 85, W Bridge St
Colorado US Highway 87, US-87
Colorado US Highway 96, US-96
Colorado US Highway 134, US-134
Colorado US Highway 138, 2nd Ave
Colorado US Highway 138, Broadway St
Colorado US Highway 138, E 1st St
Colorado US Highway 138, N 3rd St
Colorado US Highway 138, N 4th St
Colorado US Highway 138, Railroad St
Colorado US Highway 138, Saunders Ave
Colorado US Highway 138, US-138
Colorado US Highway 138, W 1st St
Colorado US Highway 160, 1st Ave
Colorado US Highway 160, 4th Ave
Colorado US Highway 160, Broadway Ave
Colorado US Highway 160, Camino del Rio
Colorado US Highway 160, Denver Ave
Colorado US Highway 160, E 5th St
Colorado US Highway 160, E Goddard Ave
Colorado US Highway 160, E Grand Ave
Colorado US Highway 160, E Main St
Colorado US Highway 160, E Sante Fe St
Colorado US Highway 160, Grand Ave
Colorado US Highway 160, Grande Ave
Colorado US Highway 160, Hwy 160 Frontage Rd
Colorado US Highway 160, Main St
Colorado US Highway 160, Mancos Rd
Colorado US Highway 160, Pagosa St
Colorado US Highway 160, Park Ave
Colorado US Highway 160, Railroad St
Colorado US Highway 160, Randolph St
Colorado US Highway 160, S Broadway
Colorado US Highway 160, S Camino del Rio
Colorado US Highway 160, San Juan St
Colorado US Highway 160, Santa Fe Ave
Colorado US Highway 160, Santa Fe St
Colorado US Highway 160, US-160
Colorado US Highway 160, US-160 Bus
Colorado US Highway 160, W 7th St
Colorado US Highway 160, W Main St
Colorado US Highway 160, W Sante Fe St
Colorado US Highway 160B, US-160B
Colorado US Highway 285, 8th St
Colorado US Highway 285, E Hampden Ave
Colorado US Highway 285, E Jefferson Ave
Colorado US Highway 285, Gunbarrel Rd
Colorado US Highway 285, Gunnison Ave
Colorado US Highway 285, Main St
Colorado US Highway 285, N Broadway St
Colorado US Highway 285, Spruce St
Colorado US Highway 285, US-285
Colorado US Highway 285, US-285 N
Colorado US Highway 285, US-285 S
Colorado US Highway 285, W Hampden Ave
Colorado US Highway 285, W Hampden Dr
Colorado US Highway 285, West Ave
Colorado US Highway 287, 3rd
Colorado US Highway 287, Buchanan Ave
Colorado US Highway 287, Cleveland Ave
Colorado US Highway 287, Clifford St
Colorado US Highway 287, College Ave
Colorado US Highway 287, E 15th St
Colorado US Highway 287, E Colfax Ave
Colorado US Highway 287, Federal Blvd
Colorado US Highway 287, Garfield Ave
Colorado US Highway 287, Main St
Colorado US Highway 287, N 107th St
Colorado US Highway 287, N College Ave
Colorado US Highway 287, N Lincoln Ave
Colorado US Highway 287, N Main St
Colorado US Highway 287, S 112th St
Colorado US Highway 287, S Cleveland Ave
Colorado US Highway 287, S College Ave
Colorado US Highway 287, S Lincoln Ave
Colorado US Highway 287, S Main St
Colorado US Highway 287, US-287
Colorado US Highway 287, W 3rd Ave
Colorado US Highway 287, W 15th St
Colorado US Highway 287, W 120th Ave
Colorado US Highway 287, W Colfax Ave
Colorado US Highway 287, Wansted St
Colorado US Highway 350, Barnes Ave
Colorado US Highway 350, Potter Dr
Colorado US Highway 350, US-350
Colorado US Highway 350, W 5th St
Colorado US Highway 350, W Main St
Colorado US Highway 385, 8th St
Colorado US Highway 385, Borders St
Colorado US Highway 385, Colorado Ave
Colorado US Highway 385, County Road HH
Colorado US Highway 385, Dexter St
Colorado US Highway 385, E 5th St S
Colorado US Highway 385, E Olive St
Colorado US Highway 385, Main St
Colorado US Highway 385, N Dexter St
Colorado US Highway 385, N Interocean Ave
Colorado US Highway 385, N Labelle Ave
Colorado US Highway 385, N Labelle St
Colorado US Highway 385, N Main St
Colorado US Highway 385, S 2nd St E
Colorado US Highway 385, S Interocean Ave
Colorado US Highway 385, S Labelle St
Colorado US Highway 385, S Lincoln St
Colorado US Highway 385, S Main St
Colorado US Highway 385, South 2nd St E
Colorado US Highway 385, US-385
Colorado US Highway 385, W 2nd St N
Colorado US Highway 385, W Goff Ave
Colorado US Highway 385, West 1st St N
Colorado US Highway 385, West 1st St S
Colorado US Highway 400, E Colorado St
Colorado US Highway 400, E Goff Ave
Colorado US Highway 400, W Colorado St
Colorado US Highway 491, N Broadway
Colorado US Highway 491, US-491
Colorado US Highway 550, Camino del Rio
Colorado US Highway 550, Main Ave
Colorado US Highway 550, Main St
Colorado US Highway 550, N Main St
Colorado US Highway 550, S Townsend Ave
Colorado US Highway 550, US-550
Colorado US Highway 85/87, US-85 87