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Traffic disruptions, closures around Boulder for Saturday’s Ironman 70.3 race

By Jonathan Ingraham June 12, 2025 | updated 2 months ago

Competitor dies in swim leg of Boulder Ironman triathlon

Boulder Reservoir, where the swimming portion of the Boulder Ironman takes place. Photo Credit: SWKrullImaging (iStock).

SWKrullImaging

Competitor dies in swim leg of Boulder Ironman triathlon

Boulder Reservoir, where the swimming portion of the Boulder Ironman takes place. Photo Credit: SWKrullImaging (iStock).



SWKrullImaging


Heading to Boulder, Colorado for the annual Ironman 70.3 race at Boulder Reservoir? Plan ahead…

The Ironman 70.3 Boulder race returns to Boulder Reservoir on Saturday and several traffic and travel restrictions in north Boulder will be in place during the day, Boulder County said on Thursday.

All residents will have access to their homes, but may encounter delays and should follow recommended detours. 

“If you are traveling through the area during the event please pay close attention to the Boulder County Sheriff, Colorado State Patrol, and the volunteer traffic marshals who will be helping to ensure safety for riders and travelers alike,” the County said.

“When passing a bicyclist, motorists must allow at least three feet of space between their vehicle and a bicyclist. To pass a bicyclist safely, drivers may cross a double yellow center line when oncoming traffic is clear.”

Travel Restrictions

The bike course will active between 7 a.m. and 2 p.m. on Saturday and will use the following roads:

CO 119/Diagonal Highway, N. 63rd St., Monarch Rd., Jay Rd., US 36/N. Foothills Hwy, H Rd., and N. 75th St./N. 73rd St., and 71st St.

Download PDF PDF preview

Ironman 70.3 Boulder bike map for 2025.

Courtesy, Ironman Boulder

  • CO 119/Diagonal Highway will remain open, one lane of westbound/Boulder bound lanes will be closed from N. 63rd St. to Jay Rd. Expect delays.
  • Jay Rd. will be closed to westbound traffic from Diagonal Highway to 28th St.
  • US 36/28th St. will be closed northbound from Jay Rd. to Hygiene. Through traffic on northbound US 36 from Boulder to Lyons should use CO 119 to Longmont, head north on Hover Rd., then west on CO 66. If heading to Estes Park, use the same route or you may also use CO 119 to Nederland, then north on CO 72 to CO 7, then continue north to Estes Park.
  • 75th St./73rd/71st St. will be closed southbound from Hygiene Rd. to Niwot Rd. Niwot Rd. will remain open for local access, expect delays
  • St. Vrain Rd. will be closed to through traffic, residents will be allowed to access their homes
  • Hygiene Rd. will be closed to through traffic, residents will be allowed to access their homes
  • Monarch Rd. will be closed from 55th St. to 71st St. Residents will be allowed to access their homes via. 55th and 63rd Streets.
  • 63rd St. will be closed from Diagonal Highway to Niwot Rd. from 7 a.m. until 5 p.m. Residents will be allowed to access their homes from Niwot Rd., but there will be no access to CO 119/Diagonal Highway.
  • 51st/55th St. will be closed to through traffic from Niwot Rd. to Jay Rd. Residents will be allowed to access their homes.
  • Do not try to cross the course. If you need to get from one side or the other use US 36 Southbound or N. 75th St. Northbound, and CO 66 to get around the bike course. Please do not attempt to get across on Hygiene Rd., Niwot Rd., Nelson Rd., St. Vrain Rd., Plateau Rd., or westbound Jay Rd. While those roads will remain open for resident access except for as mentioned above, you will experience longer delays than if you use the loop around the bike course.

Shuttles

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Featured Local Savings

All athletes and spectators must take a shuttle on race morning (unless carpooling with a volunteer). There is no alternative method to getting to the venue.

Parking/Shuttle Pick-up:

• Kyndryl Boulder (former IBM building) 6300 Diagonal Hwy Boulder. You must access from CO 119/Diagonal Hwy.

Shuttle Drop-off:

• Boulder Reservoir, 5565 North 51st St. in Boulder

For additional information, please visit the event website Athlete’s page and click on the “Parking/Shuttle Info” tab.

Recreational Cycling Impacts

Recreational cyclists should avoid traveling in the same direction as the riders on the bike course.

Boulder Reservoir Impacts

Boulder Reservoir will be closed to the public Thursday at 11 a.m. through Saturday.

Download PDF PDF preview

Ironman 70.3 Boulder run map for 2025.

Courtesy, Ironman Boulder

No watercraft of any kind will be permitted into the Boulder Reservoir all day Thursday through Saturday.

(Contact Denver Gazette digital producer Jonathan Ingraham at jonathan.ingraham@denvergazette.com or on X at @Skingraham.)

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