As part of a $30 million road widening project, a busy thoroughfare south of Denver is poised to undergo a 100-day closure beginning in early January.

Construction is already underway to widen County Line Road between University Boulevard and Broadway. The corridor, which splits Arapahoe and Douglas counties, experiences an average of 25,000 motorists a day.

Starting Jan. 6, construction crews will close both directions of County Line Road between Clarkson Street and the U-Haul business access. Officials expect road closures to last approximately 100 days and remain closed 24/7.

Crews need to import, move and place large amounts of dirt at Lee Gulch, according to Douglas County officials.

“The fill operations, which are a key component of the widening and reconstruction work, will level out the roadway by removing the dip at Lee Gulch, improving drainage, driver line of sight and overall public safety,” Douglas County officials said in a news bulletin.

The County Line Road widening and reconstruction project is a partnership between Douglas County, Littleton, Centennial and the Denver Regional Council of Governments.

Expected to be completed in September 2027, County Line Road will feature one additional lane between Broadway and University Boulevard. This includes a new traffic signal at Clarkson Street and County Line Road, a mill and overlay in Littleton between Phillips Avenue and Broadway, new sidewalks and relocated water lines.

Douglas County has prepared for County Line Road reconstruction since 2019. Douglas County and its partners hired JHL Constructors for the project.

Business access will remain open via County Line Road. Douglas County officials listed detours in place for the 100-day closure:

• Use University Boulevard to reach businesses east of the closure.
• Use Broadway to reach businesses west of the closure.
• Residential access to Clarkson Street is open via Dry Creek and County Line roads.
• Commuters traveling on County Line Road can use C-470 between University Boulevard and Broadway to bypass closures.

“This is an active construction zone,” county officials said. “Please drive posted speeds, watch for crews and equipment, and avoid distractions behind the wheel.”