CO 119 Safety & Mobility Improvements Project - Design Phase

Project Overview

The Diagonal Highway (Colorado Highway 119) between Boulder and Longmont is a high-crash corridor. Regional growth and current traffic patterns have led to safety and traffic flow issues. By 2040, the corridor is expected to see a 25% increase in vehicular traffic, which can result in more congestion, traffic delays, tailpipe emissions, and potentially more crashes. CDOT and the Regional Transportation District (RTD) are taking action to mitigate these outcomes and expand transportation options beyond private vehicles.

The CO 119 Safety and Mobility Improvements Project is designing improvements to make traveling through the corridor safer and more efficient for all corridor users, including faster and more reliable transit travel. The project is coordinating with other active multimodal projects on the corridor so community members can safely and reliably access and travel the corridor using their mode(s) of choice. Funding has been secured for implementation of the CO 119 Safety and Mobility Improvements Project, which is expected to go to bid for construction in fall 2023.


  • June 2022 Community Meeting FAQs added to website.
  • Intersection design plans added to website.
  • Design Update: Access from rom Ogallala Road to northbound Airport Road will be maintained. Visit the
    Airport Road page to learn more about design plans for this intersection.
  • The project was not awarded a 2022 Federal RAISE grant.

Project Schedule

  • Preliminary Design began late 2021
  • Final Design began mid-2022
  • Design completion mid-2023

CO 119 Schedule

(Click to enlarge)

Project Area

  • Colorado Highway 119 (CO 119) from Foothills Parkway in Boulder to Hover Street in Longmont.  
  • The Bus Rapid Transit (BRT) routes extend from downtown Boulder to Colorado Highway 66 north of Longmont.

Project Improvements

The project is designing small scale to large improvements to advance project goals of safety, traffic flow, and multimodal connectivity.


  • BRT service.
  • Synchronized traffic signals that optimize the length of green lights and promote traffic flow.
  • Adaptive signal technology that detects when vehicles, pedestrians, and bicyclists are present and adjusts the signal accordingly.
  • Intelligent Transportation Systems that enhance safety and provide real-time information to travelers.
  • Signage and pavement markings to make intersections safer and improve multimodal access.
  • First steps of a broader vision to identify future pedestrian and bicycle connections to the corridor.


  • Physical reconfiguration of the CO 52 intersection.
  • Elimination of left turns at CO 119 and Airport Road.
  • BRT stations, Park-n-Rides, and bus queue bypass lanes.
  • Lighting at intersections, Park-n-Rides, and bus platforms.

Alt text: Map showing project improvements at 5 signalized intersections between Boulder and Longmont on CO 119

  • Less fender benders and crashes
  • Vehicles can move through the corridor faster, with shorter wait times at traffic lights
  • Traveling the corridor by bus will take about half the time it currently does
  • More frequent bus service supports greater travel flexibility
  • Safer and more comfortable experience accessing the corridor on foot
  • Integration between Bus Rapid Transit, Park-n-Rides, pedestrian crossings, and Boulder County’s Commuter Bikeway enables commuters to switch travel modes safely and reliably