CDOT proposes build option to cut crashes, widen shoulders on I-25 segment through north Adams County

Colorado Department of Transportation staff described a preferred safety-and-operations package for I-25 Segment 2A (US 36 to 104th Avenue) during an Oct. 8 briefing with Adams County commissioners, saying the option aims to reduce crashes, improve transit reliability and maintain peak-period travel times.

"We are in preliminary design. We have finished 20% level, and we are working towards 30% level," said Tom McGinnis, CDOT Region 1 resident engineer for I-25 segments, describing the ongoing design and environmental process. McGinnis said public meeting No. 2 was scheduled in late October and that CDOT expects to finish a NEPA document in May and proceed to final design and right-of-way work ahead of a conservative construction start in late 2027.

CDOT presented corridor safety data in the meeting. The corridor experienced about 490 crashes in a baseline year and an existing crash rate of 1.86 crashes per million vehicle miles, staff said. Two-thirds of crashes occur in the southbound direction; staff reported an average of 205 days per year with at least one southbound crash and 119 days for northbound.

CDOT traffic and safety modeling showed a substantial reduction in projected crash counts and crash rate with the preferred alternative: staff cited an approximate 46% decrease in crash rate in the 2050 analysis relative to the no-action scenario, excluding some additional site-specific countermeasures such as upgraded signage and ramp terminal improvements.

The preferred "Build 2" alternative includes: - wider shoulders and a larger express-lane buffer to improve safety and accommodate bus breakdowns; - a climbing lane and auxiliary lanes in the northbound direction to address steep grades and merging; and - a fourth general-purpose lane in the southbound direction (capacity widening) with auxiliary lanes between interchanges.

CDOT told commissioners that the proposal removes problematic slip ramps that currently provide direct access to the Thornton Park-and-Ride; RTD has told CDOT it plans to maintain bus service to the area but will reroute buses to existing interchanges (for example, 80th Avenue) rather than using those slip ramps.

Traffic modeling showed the preferred alternative reduces peak travel times: CDOT estimated about an 11-minute PM (northbound) savings and a 5-minute AM (southbound) savings compared with the 2050 no-action forecast, and faster recovery of congestion after peak periods.

Commissioners asked for clarification on specific elements, including confirmation that the project includes a rebuild of the 80th Avenue bridge and coordination with Thornton regarding a planned typical section and sidewalks. CDOT confirmed the 80th Avenue bridge work is included and that the team is coordinating with Thornton on multi-modal accommodations.

Schedule: CDOT listed public meeting No. 2 for Oct. 22, with NEPA documentation planned for completion in May (next year) and a FONSI or decision document expected in December 2026 under the conservative schedule staff presented. Final design and right-of-way activity would follow the NEPA decision; staff projected construction could begin in late 2027 once permits and right-of-way are secured.