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 June 21 to 27, 2026

Lane Closures

On Monday, June 22, 7 p.m. to 5 a.m. overnight, there will be various single lane closures on southbound Colorado Highway 119/Diagonal Highway at the Airport Road intersection for road striping.

On Tuesday, June 23, 9 a.m. to 3 p.m., there will be a left-lane closure on southbound CO 119 at Niwot Road and at the Airport Road intersection to remove and set traffic barriers.

On Friday, June 26, 9 a.m. to 3 p.m., there will be northbound and eastbound lane closures at the Hover Street and CO 119 intersection for drilling work.

Phase 3 of Airport Road Safety Improvement Work

On Monday, June 22, crews will transition to the Phase 3 of safety
improvement work at the Airport Road and CO 119/Diagonal Highway intersection. This final phase is anticipated to last approximately several Phase 3 traffic impacts:

  • Closure of one southbound lane on Airport Road, just north of southbound CO 119/Diagonal Highway. The designated right-turn lane on southbound Airport Road is open
  • Airport Road northbound median reduced to one lane
  • Left shoulder closure on southbound CO 119/Diagonal Highway
  • Pedestrians and cyclists can use the underpass under Airport Road to access the northwest crossing to cross southbound CO 119/Diagonal Highway
  • RTD bus stop on southbound CO 119/Diagonal Highway at Airport Road will be closed

Fourmile Canyon Creek Trail Closure

Beginning Thursday, June 25, the segment of Fourmile Canyon Creek multiuse path, between 47th Street and Foothills Parkway, will be closed as crews construct bikeway connections. This closure is expected to last until late 2026.

Detour:

From northbound CO 119: Turn south on the trail at CO 119/Diagonal
Highway, continue toward Independence Road, and north onto 47th Street to reconnect to the Fourmile Canyon Creek trail.

From 47th Street: Turn south on the trail, continue to the Foothills
Parkway/CO 119 interchange and continue north on CO 119/Diagonal
Highway.

From southbound Foothills Parkway: Continue south toward the Foothills

Parkway/CO 119 interchange (near Mountain View Memorial Park) to
reconnect to the Fourmile Canyon Creek trail.

Overnight Intersection Closure at Hover Street and CO 119 - Sunday, June 28

On Sunday, June 28, 7 p.m. to 5 a.m., the Hover Street and CO 119/Diagonal Highway intersection will be closed to all modes of transportation as crews switch the intersection to temporary traffic signals.

Detour Routes:

Southbound Ken Pratt Boulevard: Turn right at the intersection onto Hover Street, turn left onto Nelson Road, turn left onto South Fordham Street and turn right onto southbound CO 119.

Southbound Hover Street: Use right turn lane to continue onto southbound CO 119.

Northbound Hover Street: Turn right at the intersection onto Ken Pratt Boulevard, turn left onto Sunset Street, turn left onto Nelson Road and turn right to return to northbound Hover Street.

Northbound CO 119: Make a sharp right at the intersection onto southbound Hover Street, turn left onto Pike Road, turn left onto Sunset Street and turn right onto northbound Ken Pratt Boulevard.

63rd Street Overnight Median Closure

On Tuesday, June 30, 6 a.m. to 5 p.m., the 63rd Street median between northbound and southbound CO 119/Diagonal Highway will be temporarily closed to all modes of transportation as crews install the bikeway overpass.

Detour:

Northbound 63rd Street travelers: Turn right onto northbound CO 119, turn left at Colorado Highway 52, and turn left onto southbound CO 119 to return to 63rd Street

Southbound 63rd Street travelers: Turn right onto southbound CO 119, turn left onto Jay Road and turn left onto northbound CO 119 to return to 63rd Street.

Ongoing Closures

South Fordham Street Median Closure - Through 5 p.m., Monday, June 22

The South Fordham Street median between northbound and southbound CO 119/Diagonal Highway is temporarily closed to all modes of transportation. This closure allows crews to remove asphalt and install a raised crossing, improving safety for people traveling through the corridor.

Phase 2 of Airport Road Safety Improvement Work - Through Monday, June 22

On Monday, June 8, the ongoing safety improvement work at the Airport Road and CO 119 intersection transitioned to Phase 2.

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!