I-25 (US 36 to 104th Ave) Improvements Environmental Assessment (EA) Draft

About the Draft EA

The focus of the project is the I-25 corridor between US 36 and 104th Avenue in Northglenn and Thornton. This project is now in the NEPA phase.


In 2011, CDOT completed the North I-25 Final Environmental Impact Statement, Final Section 4(f) Evaluation (FEIS), and North I-25 Record of Decision 1 (ROD1). The FEIS identified and evaluated multimodal transportation improvements along the 61-mile I-25 transportation corridor extending from the Fort Collins/Wellington area to Denver. Between US 36 and 104th Avenue, the elements of the ROD1 Preferred Alternative that have been constructed include:

  • Six 12-foot general-purpose lanes (three in each direction)
  • Two 12-foot Express Lanes (one in each direction)
  • A concrete barrier between the northbound and southbound directions of the roadway
  • Tolling and intelligent transportation system infrastructure
  • Four new noise walls and the rehabilitation of existing noise walls

The elements of the ROD1 Preferred Alternative that have not been constructed include:

  • A 4-ft buffer along the inside travel lane between the Express Lane and general-purpose lane (one in each direction)
  • 12-ft inside and outside shoulders in each direction
  • Replacement of the 88th Avenue bridge over I-25

CDOT completed the North I-25, US 36 to CO 7 Planning and Environmental Linkages (PEL) study in 2014 The North I-25, US 36 to CO 7 PEL study evaluated improvements to reduce congestion and improve safety on I-25 between US 36 and CO 7 by implementing near term, multimodal, and cost-effective transportation improvements that were compatible with long-term options and the recently constructed interchange structures along the corridor, including the I-25/84th Avenue interchange.

Within the project area the PEL Recommended Alternative included:

  • Adding a fourth 12-ft general-purpose lane in each direction from 84th Avenue to Thornton Parkway
  • Constructing 12-ft continuous acceleration and deceleration auxiliary lanes between the I-25/104th Avenue interchange and the I-25/Thornton Parkway interchange
  • Reconstructing the Thornton Park-n-Ride to include an I-25 median transit station accessed by an above-ground pedestrian bridge

In 2017, FHWA, in conjunction with CDOT and local agencies, completed the I-25 North Metro Managed Lanes Road Safety Audit (RSA) Report, which evaluated conditions along and identified safety enhancements for the I-25 corridor from US 36 to 112th Avenue. CDOT has implemented many of the safety enhancements recommended in the 2017 RSA. The implemented safety enhancements include educational outreach, enhanced law enforcement, and several roadway maintenances and engineering improvements. Roadway improvements have included signing and striping improvements, the implementation of queue warning systems, the addition of shoulder pull-out areas in select locations, rumble strips, and on-ramp modifications.

In 2020, the project team initiated the National Environmental Policy Act (NEPA) and Preliminary Design phase of work. This project followed the CDOT and Federal Highway Administration (FHWA) NEPA process to:

  1. Examine the needs for improvements to the project area
  2. Identify the Proposed Action
  3. Investigate the anticipated benefits and impacts of the proposed improvements (through an Environmental Assessment)
  4. Produce preliminary design plans
  5. Public input from the PEL process and agency input was used in the decision-making process

In May of 2020 CDOT determined that additional studies were needed to evaluate transit alternatives. As a result, the Environmental Assessment (EA) document from 2020 was put on hold. The EA has  remained unsigned, and therefore not published. The NEPA process initiated for the proposed action presented in the EA was not completed.

Additional studies have been completed for the I-25 (US36 to 104th Ave) corridor since the previous NEPA effort. These include:

· 2021 - White Paper #1, North I-25 (US 36 to 104th Ave) Supplemental Options Analysis

· 2022 - I-25/I-270/US 36 Express Lanes Direct Connects Interchange Development Plan

· 2023 - White Paper #2, Safety & Transit Impacts Analysis

These studies have provided recommendations for transit, safety and operational improvements, and through alternatives screening have presented a proposed action for the corridor. 

In 2024, the project team is reviewing this updated proposed action by initiating a new NEPA and Preliminary Design phase for the I-25 (US36 to 104th Ave) Safety Improvements Project.