United States Highway 85 (U.S. 85) travels from the Canadian border in North Dakota to the Mexican border in El Paso, Texas, through the country's Mountain and Northern Plains states. In Colorado, this regional highway serves as a major conduit for interstate commerce, the movement of goods and services, and daily commuters’ trips to and from work, school, and home.

Part of the Denver-Aurora-Lakewood metropolitan statistical area, nestled along Interstate 25 between Colorado’s two largest cities, Douglas County is both a magnet for businesses and a destination for outdoor recreation. The Douglas County segment of U.S. 85, just south of Colorado State Highway 470 (C-470), currently carries approximately 45,000 vehicles daily. This number is anticipated to nearly double by 2040, with an estimated increase to more than 80,000 vehicles.

The route provides access to local commercial and industrial businesses and nearby major employment areas. It is heavily traveled by area residents living in Highlands Ranch, Roxborough, Sterling Ranch, Louviers, Sedalia, the Town of Castle Rock, and unincorporated Douglas County, as well as by commuters traveling to Denver from destinations in the south metro area, and in-state and out-of-state tourists accessing nearby state parks and the Rocky Mountain I-70 corridor. Additionally:

• U.S. 85 is a national defense corridor and a national freight corridor.
• U.S. 85 is an alternative route for I-25 should an incident occur on the interstate that closes or greatly impacts the segment of I-25 south of Denver.
• U.S. 85 provides an entrance to Chatfield State Park and Roxborough State Park.

Increased development and employment growth have strained the highway's capabilities, indicating a critical need for widening and other improvements. To address these issues and add multi-modal enhancements, Douglas County partnered with the Colorado Department of Transportation (CDOT) to implement the current U.S. 85 Corridor Improvements Project by improving 2.5 miles of U.S. 85 (known locally as Santa Fe Drive), from Highlands Ranch Parkway extending a half mile north of C-470 to Dad Clark Gulch.

“Widening and reconstructing the segment of U.S. 85 between Highland Ranch Parkway and C-470 is consistent with the goals and objectives of improving the overall U.S. 85 corridor between I-25 and C-470,” Douglas County Project Director Art Griffith said. “Congestion, safety, lack of multi-modal infrastructure, and the need to accommodate anticipated population growth were factors in determining the improvements that are now being implemented.

“This project will improve access and mobility for all modes of transportation, while addressing safety concerns, related traffic congestion, and access to businesses. It replaces existing outdated infrastructure, provides a closed stormwater sewer system, improves seven RTD [Regional Transportation District] bus stops, helps reduce congestion and traffic delays, thereby reducing greenhouse gas emissions, and incorporates over $30 million in improvements for multi-modal infrastructure.

“This project is the largest single transportation improvement project that Douglas County has managed from start to finish.”

Construction began in October 2022 and is expected to be completed in the fall of 2025. Major components of the project include:

• New additional through lanes in each direction
• A new, wider bridge over C-470 with updated on- and off-ramps, including a new continuous flow intersection (CFI) from northbound U.S. 85 to westbound C-470
• Over 2.5 miles of new pedestrian and cyclist paths from north of C-470 to Highlands Ranch Parkway
• Two new trail underpasses (C-470 and High Line Canal Trails)
• New pavement and medians throughout the corridor
• Signal replacements/updates with timing adjustments
• Major utility relocations
• Storm water drainage improvements

These improvements are designed to increase safety, mobility, and ease traffic operations in multiple ways:

• The addition of safe multi-mobility options for traveling the corridor (car, walk, bus, bicycling)
• Reduction of left-turn conflicts throughout the corridor, specifically at non-signalized intersections
• Reduction of traffic backups due to additional through and turn lanes

“In recent years, Douglas County partnered with CDOT on several other improvements along the U.S. 85 corridor, generally located between C-470 on the north end and I-25 on the south end,” Griffith said. “Since U.S. 85 is a state-owned highway, CDOT is ultimately responsible to operate and maintain the U.S. 85 corridor. However, the county is the primary governmental agency responsible for managing this project through both the design and construction phases, while CDOT and FHWA [the Federal Highway Administration] provide general oversight.

“The developers located in the Chatfield Basin, namely Sterling Ranch and the Shea/Solstice developments, are major financial contributors to these U.S. 85 improvements through commitments made as part of their development agreements with Douglas County.”

The primary contractor for the U.S. 85 Corridor Improvements Project is Kraemer North America. There are over 45 specialized subcontractors on the project as well. RockSol, Emprise, and Benesch are providing consultant services for construction management, inspection, and material testing. Project designers include HDR, Woolpert, WSP, and Yeh & Associates.

The total project cost estimate is $130 million, including costs for construction, design, right of way (ROW) acquisitions, and utility relocation. An additional estimated $30 million in utility relocations were performed and paid for by third-party utility companies. Griffith said the current construction contract amount is for approximately $101.3 million.

“Douglas County paid 100 percent of all the preconstruction costs,” he said. “Federal funding for the construction phase totals $29,773,000, with the majority of these federal funds being allocated via the Denver Regional Council of Governments through the Transportation Improvement Program project selection process. CDOT is contributing $3.6 million, while Douglas County is responsible for the remainder of the project costs.”

The project has been phased in order to keep two lanes of traffic flowing in both directions on U.S. 85 during high-volume traffic periods, reducing traffic impacts. There have been only a few exceptions when full or partial closures were required for specific construction operations, mainly associated with the bridge work. The project has implemented multiple traffic shifts on U.S. 85 and temporary alignment changes at intersecting streets to keep traffic flowing while opening new work areas.

One example of this phasing is the construction of the new bridge that carries U.S. 85 over C-470. Kraemer North America built half of the new bridge to the west of the existing bridge first.

“Then in December 2023, we moved all six lanes of U.S. 85 traffic onto the western half of the new structure,” Griffith said. “In March 2024, we demolished the existing bridge that was built about 60 years ago. The old bridge was a cast-in-place concrete bridge, and demolition plans were very complex. Blasting was considered, but that option was eliminated due to risks.

“Kraemer completed the demolition in only two and a half days without incurring any damage to the existing C-470 concrete pavement, by cushioning the highway below with enough dirt to cover a football field, twice. Crews worked around the clock, while the C-470/U.S. 85 interchange was fully closed, and C-470 mainline traffic was diverted to the off- and on-ramps.

“The public outreach plan, which included coverage from the major news networks, did a great job getting the message out to the public to avoid this area and helped reduce backups during the extended weekend closure, which kept traffic delays to a reasonable 10 to 15 minutes. The girders on the second half [east half] of the new U.S. 85 bridge were set in late June 2024, and the deck pour was completed the first week of August 2024.”

The old bridge over C-470 consisted of seven lanes, including only two through lanes in each direction. The newly constructed bridge has three through lanes in each direction, double left-turn lanes with additional storage for the heavy northbound U.S. 85 to westbound C-470 traffic movement, and a single left-turn lane for southbound U.S. 85 to eastbound C-470, which supplements the existing dedicated southbound flyover ramp that exits U.S. 85 a half mile north of C-470.

“One unique feature the project is incorporating is partial continuous flow intersections that will improve traffic operations for heavy traffic movements, like for northbound U.S. 85 to westbound C-470,” Griffith said. “This design requires displacing this left-turn movement and crossing it over southbound U.S. 85 traffic — utilizing an additional traffic signal — in advance of the C-470 interchange complex.

“The new bridge will also provide a 10-foot sidewalk along the west side of U.S. 85, connecting the Wolhurst Senior Community with the C-470 Trail and Chatfield State Park. Previously there was no bicycle/pedestrian infrastructure along U.S. 85 within the entire project limits.”

Two new grade-separated trail crossings under U.S. 85 are being installed along high-volume bicycle/pedestrian trails — one at the C-470 Trail and another at the High Line Canal Trail. Additionally, the project includes a new multi-use trail along the eastern side of U.S. 85 from C-470 south to Highlands Ranch Parkway, which includes constructing a grade-separated crossing under the BNSF Railway and the Union Pacific Railroad.

“The C-470 Trail is already recognized as one of most important regional trails that connects the mountains to the plains, and the High Line Canal Trail traverses 78 miles through the south and east Denver metro area,” Griffith said. “The trail along the east side of U.S. 85 ties into Douglas County’s east-west trail, which extends east thru Highlands Ranch, Lone Tree, and connects to the Town of Parker.”

Currently, most of the utility relocations have been completed, apart from a few remaining critical gas and electric relocations. The majority of underground storm water sewer infrastructure work and almost all retaining wall construction is completed, along with most removals required for future improvements.

"Given the project challenges with utility relocates and traffic volumes, the progress to date is truly remarkable,” said Mike McNish, Kraemer North America Area Manager. “This is attributed to the collaboration and partnership between Douglas County, CDOT, and Kraemer to work together and solve problems expeditiously."

“As of [the time of writing this article], most roadway reconstruction and widening has been completed,” Griffith said. “Martin Marietta Materials Inc. has placed most of the bottom and middle mat of asphalt paving. It is anticipated that they will place most of the top mat of stone matrix asphalt in the second quarter of 2025.

“In the fall of 2024 and into 2025, Kraemer will complete the new multi-modal trail along the east side of U.S. 85. The remaining phases include finishing operations, landscaping, final striping, sign installations, and moving traffic into final alignment. Douglas County motorists and regional travelers can expect improvements to be completed in fall 2025.”