County Line Road Closes March 19-21 for Underground Crossing Installation

Crews working on the $30 million County Line Road Widening and Reconstruction Project closed a stretch of the road between Clarkson Street and Phillips Avenue for alternating lane operations and hard closures March 19-21, pausing traffic along one of the busiest arterials connecting Highlands Ranch, Littleton and Centennial while they installed underground crossings beneath the corridor.

The hard closure portion began at 7 p.m. Thursday, March 19, though the exact end time was not fully confirmed in available notices. The short-term operations represented a distinct activity within the larger 100-day full closure that Douglas County launched January 6 between Clarkson Street and the U-Haul business access, a stretch that averages about 25,000 road users each day.

Douglas County project manager Cori Cowan has described the scope of what crews are working through: "bringing the grade up several feet and adding sound walls." The underground crossing installation falls within that broader earthwork phase, which also requires crews to import significant amounts of dirt for construction at Lee Gulch, filling what locals have long called the "roller coaster" dip along the corridor.

The full closure between Clarkson and the U-Haul access, running Monday through Friday from 7 a.m. to 7 p.m. with possible Saturday work under Douglas County approval, was expected to lift around mid-April 2026. Drivers navigating around the closure have been directed to use University Boulevard for east-side business access and Broadway for the west side. Access to Clarkson Street has been maintained throughout.

The County Line Road project, a collaboration among Douglas County, the City of Littleton, the City of Centennial and the Denver Regional Council of Governments, has been in the works since 2019, when Douglas County began acquiring right-of-way and designing utility relocation alongside contractors Benesch and JHL Contractors and the Highlands Ranch Metro District. Construction began in September 2025.

When complete in September 2027, the reconstructed road will carry four lanes instead of two, with a new traffic signal at the Clarkson Street intersection, new sidewalks, a sound wall and a mill-and-overlay resurfacing of the Littleton segment between Phillips Avenue and Broadway. Centennial Mayor Stephanie Piko captured the road's standing in the community at the project's groundbreaking: "County Line Road is one of those topics that comes up often. It holds a lot of nostalgia."

Residents with questions about the project can reach the Douglas County project hotline at 720-795-9622, extension 2523.