CO 119 Safety, Mobility & Bikeway | Construction Phase

About the Project

By the year 2040, the Diagonal Highway between Boulder and Longmont is expected to see a 25% increase in vehicular traffic. Increased traffic can result in more congestion, delays, tailpipe emissions and potentially more crashes. CDOT, the Regional Transportation District and Boulder County are taking action to mitigate these outcomes and expand transportation options.

The CO 119 Safety, Mobility and Bikeway project will make improvements to the corridor, resulting in safer, faster and more reliable travel for all modes of transportation. The project spans Colorado Highway 119/Diagonal Highway, between Boulder and Longmont, from approximately Foothills Parkway to Hover Street. The project is designed to integrate with other active multimodal projects on the corridor.

Project Facts

  • Program Cost: $165 million
  • Contractor: Kraemer North America
  • Timeline: Fall 2024 to Spring 2027
  • Location: CO 119 between Boulder and Longmont
    • Nearest Towns/Cities: Boulder and Longmont
    • Mile Point(s): 44.5 to 54.5
    • County: Boulder

To sign up for the weekly construction update emails, follow these steps:

  • Select the "Sign up for CO 119 Mobility Project Updates" button on the right side of the page
  • Scroll to the "Construction Updates & News Releases" section, select "Subscribe to Construction Updates"
  • Enter your email address, select "Northeast Colorado" as the region, check "Front Range I-25 Corridor" and "CO 119 Safety & Mobility Improvements"
  • Submit!

The Construction Manager/General Contractor (CM/GC delivery method) is being used to build the project. Construction started in September 2024.

Check out the online presentation videos to learn more about the safety, mobility, and bikeway improvements. Email [email protected] if you wish to receive this presentation in Spanish.

Project Area

CO 119 Safety & Mobility Project Map
Map showing the CO 119 Safety, Mobility, and Bikeway Project, highlighting proposed project elements between Boulder and Longmont, Colorado.

Key features include:

  • Bus Rapid Transit (BRT) Stations: Marked with red bus icons along CO 119
  • Park-n-Ride Locations: Indicated with blue "P" icons at various stations
  • Operational & Safety Improvements: Shown with green intersection icons
  • Bus Queue Bypass Lanes: Denoted with a gray bus with a green arrow

Proposed RTD BRT Routes:

  • Blue Line (DF1): Minimum of 30-minute weekday service and up to 30-minute weekend service between Longmont and Downtown Boulder Station via 28th Street
  • Orange Line (DF2): Up to 30-minute AM and PM peak service, weekdays only, between Longmont and Boulder via Boulder Junction at Depot Square Station
  • A list of all stops associated with the proposed BRT service is available by downloading the RTD Diagonal Flyer Stop List from the Denver RTD website.

Additional features:

  • Intersection reconfiguration at CO 52/Mineral Road
  • Northern and southern project limits marked in Longmont and Boulder, respectively

Major roads and highways are also labeled, including Airport Road, Hover Street, Niwot Road, Lookout Road, Jay Road, CO 52/Mineral Road, CO 119 and CO 157.

Project Improvements

  • Addition of a commuter bikeway (Diagonal Bikeway) with several local connection points between northbound and southbound CO 119. Underpasses or overpasses will be added at major intersections for safe and uninterrupted cyclist crossing
    • Four underpasses
      • CO 119 underpass
      • Niwot Road underpass
      • CO 52 underpass
      • Jay Road underpass
    • One overpass
      • 63rd Street overpass
  • New signage, striping and improved signal timing at all pedestrian crossings at signalized intersections
  • Signal timing adjustments at key intersections (Jay Road, 63rd Street, CO 52, Niwot Road and Airport Road)
  • Physically reconfiguring the CO 52 intersection to improve safety and to accommodate new Bus Rapid Transit (BRT) stations and the Diagonal Bikeway between the northbound and southbound travel lanes
  • Changing access at Airport Road and CO 119 to reduce crashes and to improve safety and traffic flow
  • Changes to unsignalized intersections (55th Street, Monarch Road, Oxford Road and 83rd Street (pair) and Fordham Street) to increase driver safety and prevent crashes.
Map showing the planned CO 119/Diagonal Bikeway, highlighting underpass and overpass additions and bike and pedestrian path connections between Boulder and Longmont, Colorado
Map showing the planned CO 119/Diagonal Bikeway, highlighting underpass and overpass additions and bike and pedestrian path connections between Boulder and Longmont, Colorado.

Project Goals

  • Improve safety in the whole corridor
  • Maximize the number of people able to move through the corridor
  • Maximize intersection operational efficiency
  • Improve transit travel times and increase ridership
  • Maximize corridor-wide operational efficiency
  • Increase opportunities for bicycle commuting and connectivity to the bicycle and pedestrian network

Project Benefits

  • Vehicles can move through the corridor faster, with shorter wait times at traffic lights, resulting in fewer crashes
  • 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 environment for pedestrians and cyclists accessing the corridor
  • Integration between Bus Rapid Transit, Park-n-Rides, pedestrian crossings and the Diagonal Bikeway enables commuters to switch travel modes safely and reliably

Project Schedule

  • Construction began in September of 2024
  • The project is scheduled for completion in Spring of 2027

Traffic Impacts

Week of May 17 to 23, 2026

Lane Closures

Tuesday, May 19 and Wednesday, May 20, 9 a.m. to 3 p.m., there will be various single lane closures on northbound Colorado Highway 119/Diagonal Highway near 55th Street, Oxford Road and Airport Road for traffic barrier removals and road striping.

Temporary Trail Closure at Airport Road

Beginning Monday, May 18, the multi-use trail at Airport Road between northbound and southbound CO 119 will be temporarily closed to all travelers. This closure will last through Friday, May 22, and is required to construct a new bikeway connection. Pedestrians and cyclists are advised to avoid the Airport Road intersection and use alternate routes.

During this time, (Monday, May 18 to Friday, May 22) both RTD bus stops at Airport Road and CO 119/Diagonal Highway (Stops #18005 and #19973) will be temporarily closed for pedestrian safety.

All other closures at Airport Road will remain the same as crews continue Phase 1 of safety improvement work:

Right lane and right turn lane closure on southbound Airport Road, just north of CO 119/Diagonal Highway. This closure is necessary to construct planned safety improvements including a raised crosswalk and island.

Northbound Airport Road median reduced to one lane while the left lane is closed.

Partial closure of the trail at Airport Road between northbound and southbound CO 119/Diagonal Highway.

Detours and Alternate Routes:

Use 83rd Street to access northbound CO 119/Diagonal Highway. Travelers turning right from southbound Airport Road onto southbound CO 119/Diagonal Highway can turn from the southbound lane.

CO 52 and South Fordham Street Closures Postponed
The temporary, full closures of CO 52 (between CO 119 and 71st Street) and South Fordham Street median planned for May were postponed due to weather and scheduling changes and will now begin as soon as early June.

More details will be added as dates are confirmed.

Traffic-Pacing Operations

Intermittent traffic-pacing operations will occur on CO 119/Diagonal Highway throughout construction while crews move equipment across the highway. Traffic will move slower and may result in brief traffic holds as part of this work. Please be patient and do not pass the traffic-pacing vehicles — passing them poses a safety risk to all drivers on the road. Thank you for your patience!

Respect the Cone Zone

As you travel through the construction zone, please stay in designated traffic areas. The construction site is strictly off-limits for drivers, cyclists and pedestrians. Entering between barriers or cones at any time is extremely unsafe for travelers and project crews. Law enforcement is on site regularly to monitor traffic, and fines are doubled in the construction zone.

Colorado Speed Enforcement Program

The Colorado Speed Enforcement program is active in the CO 119 Safety, Mobility and Bikeway work zone. The program addresses high speeds by using camera technology to track and enforce speed limits. Learn more by visiting the Colorado Speed Enforcement program page.

Help Ease Traffic: Explore Alternative Transportation During Construction

Hey, drivers! We know construction along CO 119/Diagonal Highway can be a hassle, and we're working hard to improve this corridor for everyone. In the meantime, we encourage the use of alternate modes of transportation to help reduce traffic and make your commute easier. Whether it’s carpooling, biking or using public transit, every little bit helps ease congestion and keep things moving smoothly for everyone.

Thanks for your patience and support – we’ll get there faster together!