Construction on the CO 119 Bikeway is On Track to Start This Fall

Project Background Information

CO 119, commonly referred to as “The Diagonal Highway”, spanning from Boulder to Longmont is expected to see a 25% increase in vehicular traffic by the year 2040. Increased traffic can result in more congestion, delay, tailpipe emissions, and potentially more crashes. The Colorado Department of Transportation (CDOT), the Regional Transportation District (RTD), and Boulder County are taking action to mitigate these outcomes and expand transportation options beyond private automobiles.

The CO 119 Safety, Mobility and Bikeway Project is constructing improvements to make traveling through the corridor safer for all modes and transit travel faster and more reliable. The project is designed to integrate with other active multimodal projects on the corridor to ensure community members can safely and reliably travel throughout the corridor using their mode(s) of choice.

Bikeway Update as of 5/23/2024

(source: Boulder County)

Construction is on track to start this fall! This is very exciting for the design team and for those that are eager to ride the bikeway. Details on where construction will start will be coming in late summer.

Planned Underpass at N. 63rd Street to be Built as an Overpass

Late in the design process a large underground water line was discovered and it is in the way of the planned bikeway underpass at N. 63rd Street and another water line is in the way of the planned bikeway crossings near the southern terminus of the bikeway. Moving the water line would cost more than $3 million dollars and would delay the completion of the bikeway by more than one year.

The CO 119 Bikeway design team compared the cost and delay of moving the waterline to replacing the planned underpass at N. 63rd Street with an overpass. After much consideration the team is recommending that the planned underpass at N. 63rd Street be built as an overpass.

The overpass would be the same steepness as the underpass. The overpass or underpass would meet ADA standards with nothing steeper than a 5% grade. An overpass or an underpass are similar steepness and grade change in this location. The overpass would be a little bit longer than the underpass.

The design team will be asking the Board of County Commissioners to amend the application of projects that are of statewide significance to approve the overpass at 63rd and the new bikeway connection to Fourmile Canyon Creek Trail.

This rendering is an example of the size and scale of a typical bike overpass and how it would look compared to the surroundings, including the view of the mountains. The design team will be asking for your input on the actual look and design of the bridge this summer.

Bikeway Connection to Fourmile Canyon Creek Trail near the southern end of the bikeway

The CO 119 Bikeway design team researched many possible solutions to the southern terminus where the bikeway will intersect with the Fourmile Canyon Creek Trail. The team developed four possible reroutes and weighed such issues as bikeway user experiences, cost, out of direction travel and project delays. The other options were millions of dollars more than this option. One option would have brought the bikeway right next to traffic. This option keeps cyclists far from motorized traffic.

After much consideration the team is recommending that the bikeway stay in the median and come in between CO 119 north and south bound lanes to the Fourmile Canyon Creek Trail. The entire bikeway, including this section will meet ADA standards and be 5% steepness or less.

This option does include a bridge over Fourmile Canyon Creek that would be under the 2–5-year floodplain and would require an occasional detour using Jay Road and 47th Street. The plan is to have the warning of the detour well marked so bikeway users will know when the detour route should be taken.

 Bikeway would come between CO 119 to connect to Fourmile Canyon Creek trail (approximately where the people in this photo are standing).
Graphic showing the new connection of the bikeway, the 119 Bikeway is shown in green.

For more information visit, or contact Alexandra Phillips, Boulder County Bike Planner, at or 303-441-4520.

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