Boulderthon Marathon Set for Sept. 28, Traffic Delays Expected

Boulder County, Colo. – The Boulderthon Marathon, along with the Half Marathon, 10K, and 5K events, is scheduled to take place on Sunday, Sept. 28, 2025, in Boulder County and the City of Boulder. Local officials advise that travelers in the area may experience delays and are encouraged to use recommended detours.

From 7 a.m. to 4 p.m. on race day, a large number of runners will utilize various roads including Jay Road, 51st Street, and sections of Pearl, Spruce, and Folsom Streets, among others. Residents living near the race courses will have access to their homes, but drivers should plan to avoid the race route to ensure smooth travel. Pilot cars will manage access in some neighborhoods, and law enforcement will guide traffic.

The Boulder County Sheriff and City of Boulder Police will oversee safety for both participants and travelers during the event. “It’s important for everyone on the road to be cautious and attentive,” an official stated. “We ask that drivers adhere to instructions from race marshals and police to help maintain safety.”

Anyone with questions or concerns can reach Boulderthon’s Community Coordinator at 970-610-0556 or contact John Holste, the Boulder County Special Events Supervisor. Additional information on traffic impacts can be found on the Boulder County website.

In addition, the event will include specific road closures, and the Boulder Reservoir will remain closed until 1 p.m. Participants and spectators should stay informed of route alterations and road closure updates as race day approaches.