I-25 (US 36 to 104th Avenue) Safety & Operations Improvements Study

About the Project

This project is in the study phase to evaluate improvements to traffic operations and safety on I-25 between US 36 and 104th Avenue. This stretch of I-25 has seen a steady increase in crashes since 2012 – most of these rear-end crashes that are typically associated with congestion.

Project Area

The project area is approximately a five-mile segment of I-25 from US-36/I-270 to the south and 104th Avenue to the north. This urban corridor is located in Adams County and surrounded by the local communities of Sherrelwood, Welby, Federal Heights, Thornton and Northglenn.

Map of proposed transportation improvements along the I-25 corridor, spanning from US 36 to 104th Avenue.
Map illustrating proposed transportation improvements along the I-25 corridor, spanning from US 36 to 104th Avenue. A central yellow band indicates areas intended to bring the corridor to standard, flanked by dark blue lines representing a new climbing lane for northbound traffic and a general-purpose lane for southbound traffic. Orange segments highlight the addition of auxiliary lanes near major interchanges like Thornton Parkway and 84th Avenue, while dashed dark blue lines at the southern interchange denote planned ramp spacing modifications.

Schedule & Important Dates

  • NEPA process: Spring 2024 to early Spring 2027
  • Project Design: Spring 2024 to Summer 2027
  • Construction: Late 2027

 Goals
  • Improve traffic operations and safety
  • Minimize environmental, community, and climate impacts caused by the project
 Improvements Under Consideration to Improve Safety
  • A new southbound general-purpose lane from 104th Avenue to south of 84th Avenue.
  • A new northbound climbing lane from the I-76 entrance ramp to 104th Avenue
  • An expanded buffer of four feet between the Express Lanes and the adjacent general-purpose lanes
  • New continuous auxiliary lanes (northbound between the I-270 and Thornton Parkway interchanges, and southbound between Thornton Parkway and 84th Avenue interchanges)
  • Wider inside and outside shoulders
  • Realignment of the combined I-76 and US 36 on-ramp connection
  • The replacement of the 88th Avenue bridge
  • The removal of bus slip ramps at Thornton Park-n-Ride
  • The realignment of Niver Creek Trail
  • The replacement of the aging pedestrian and bikeway underpass at Thornton Park-n-Ride
 Key Findings
  • Buses servicing the Thornton Park-n-Ride cause safety and operational issues when weaving to and from the outer slip ramps to access the I-25 North Express Lanes.
  • Existing and growing traffic volumes combined with increasing population and employment growth will exceed capacity and increase travel demand by 2050.
  • The crash rate in this corridor has steadily increased since 2012 with the predominant crash type being rear-end collisions that are typically associated with congestion.
Ongoing Stakeholders Coordination
  • The project team has been coordinating with RTD on the proposed design changes to the Thornton park-n-ride including the removal of slip ramps, pedestrian underpass replacement and potential adjustments to transit services.
  • City of Thornton and CDOT engineers have been working together to progress the design and details for the 88th Ave bridge replacement, which is intended to align with the City's 88th Avenue Corridor Study.