Two road closures will begin this week in Boulder County as part of the Colorado Highway 119 Safety, Mobility and Bikeway Improvements Project. The closures affect 2nd Avenue in Niwot and the 83rd Street median between northbound and southbound CO 119/Diagonal Highway.
The Oxford Road median closure, originally planned for Friday, Sept. 12, has been postponed to spring 2026 due to upcoming drainage operations. Instead, the closure of the 83rd Street median will now start on Wednesday, Sept. 10.
Starting at 9 p.m. on Tuesday, Sept. 9, the Colorado Department of Transportation (CDOT) will close 2nd Avenue in Niwot at northbound CO 119/Diagonal Highway to allow crews to widen the median for a future Bus Rapid Transit lane. Local access on 2nd Avenue will remain available between Murray Street and the railroad tracks east of the highway. This closure will last until the end of 2025 for all modes of transportation. During this period, travelers are advised to use Niwot Road to reach northbound CO 119/Diagonal Highway.
On Wednesday, Sept. 10 at 9 p.m., CDOT will also close the median at 83rd Street between northbound and southbound CO 119/Diagonal Highway for several weeks. Access through this median will be prohibited during construction for all travel modes.
During these closures, crews plan to construct a raised bikeway crossing and widen the road to extend deceleration lanes.
Travelers should follow posted detour routes for alternate access; a specific cyclist detour is also provided:
– Northbound CO 119 travelers intending to turn left onto 83rd Street should continue past it, turn left onto Airport Road median, then turn left again onto southbound CO 119.
– Southbound CO 119 travelers wanting to turn left onto 83rd Street should pass it, turn left onto Niwot Road median, then turn left again onto northbound CO 119; this route is also signed as a cyclist detour.
Work schedules may change depending on conditions.
According to projections by CDOT, vehicular traffic along Diagonal Highway between Boulder and Longmont is expected to increase by about one-quarter by the year 2040. This growth could lead to more congestion and delays as well as higher emissions and crash risk.
The ongoing project aims to improve safety throughout the corridor while maximizing its operational efficiency for all users—including transit riders and cyclists—by integrating with other multimodal projects underway in the area.
“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.”
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