Design Speed Study (55/65mph)

CDOT has completed the I-70 Mountain Corridor Design Speed study between Glenwood Springs and Golden. The purpose of this project was to address the 55 mph vs 65 mph design speed question that was not resolved as a part of the I-70 Mountain Corridor Programmatic Environmental Impact Statement (PEIS) and Record of Decision (ROD). CDOT convened a Project Leadership Team to guide the study, which concluded in April 2016. The full report is available here.

This study has determined that most of the Corridor roadway improvements can and should be designed for 65 mph. However, in two isolated locations in the corridor— east of Idaho Springs from Floyd Hill through the Twin Tunnels (Mile Post [MP] 242 to MP 247) and west of Vail through Dowd Canyon (MP 170 to MP 173)—a lower design speed is preferable. In these two locations, a lower design speed meets the purpose and need for the project as well or better than the 65 mph design speed, and the 65 mph design speed alignments through these locations have higher environmental impacts and costs and are more complex and difficult to construct and maintain. For the Tier 2 projects in these focus areas, a 55 mph design speed is recommended; however, teams will have the flexibility to determine an appropriate design speed – lower or higher – based on current conditions, design guidelines, and evolving technology that may affect design or travel speeds.

The study encompassed a Corridor‐wide review of design speeds, identified issues, and recommended decision‐making criteria and a design speed vision for the Corridor. The report details the review of the traffic operations, roadway geometry, safety history, and environmental opportunities and constraints related to travel speeds was completed for the entire 144‐mile Corridor to provide an overall understanding of the measurable influences of these factors on design speed. The report contains more details regarding travel and design speeds in the locations where the PEIS Preferred Alternative approved roadway improvements that would require design speed decisions in future Tier 2 National Environmental Policy Act (NEPA) processes. As part of this study, CDOT also completed a Guide to Variable Speed Limits on the I-70 Mountain Corridor, which provides guidance on how variable speed limits can be used in the corridor to improve traffic flow.

The results of this study would not lead to construction but rather a tool for subsequent Tier 2 highway improvement projects which may alter I-70’s long term capacity or alignment.

If you have any questions, please contact [email protected].