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Marathon Mayhem: Denver Races Disrupt Weekend Travel
17 May
Summary
- The 20th annual Denver Colfax Marathon features eight races over two days.
- Over 28,000 runners expected to participate in marathon, half, 10-miler, and 5K.
- RTD bus and rail services face detours and delays Sunday due to race routes.
The 20th annual Denver Colfax Marathon is set to cause significant traffic and transportation impacts throughout Denver this weekend, May 17-18, 2026. The event, Denver's largest running event, anticipates over 28,000 participants across eight races spanning two days.
On Sunday, May 18, 2026, several races, including the full marathon and half marathon, will commence at 6 a.m. starting in City Park and extending through Lakewood. Roads will be subject to rolling closures from 5 a.m. to 1 p.m. as runners pass through, with continuous reopening of affected areas.
The Regional Transportation District (RTD) has announced service adjustments for both bus and rail lines. From 5:30 a.m. to noon on Sunday, May 18, 2026, detours are expected, especially for routes operating along Colfax Avenue. While a Saturday 5K race will not affect rail service, customers on affected routes Sunday should anticipate delays and plan accordingly.
