A bicyclist killed in a collision with a pickup truck during the Ironman Boulder race Sunday veered from a dedicated bike lane, hit the truck and fell on the road before she was run over, according to the Colorado State Patrol.

Michelle Walters, 34, of McCook, Neb., was riding westbound on U.S. 36, when she swerved out of a lane marked by cones that was set up to protect bicyclists in the race.

“She hit the truck and fell off the bicycle and was hit by some portion of the rear tire, or rear bumper,” Trooper Nate Reid said Monday.

Walters was struck by 55-year-old Boulder resident Timothy Lacey on U.S. 36 just north of Broadway at 9:57 a.m.

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A woman who answered the phone at a relative of Walters’ home said the family was not ready to speak about Walters or the crash.

“They will not be speaking right now. They will do something at a later time,” said the woman, who declined to identify herself.

The crash marks the fourth time a cyclist has been killed by a driver in Boulder County since late May.

“We are deeply saddened to confirm the death of one of our athletes at Ironman Boulder,” race organizers said in a statement released Sunday. “We are working with the Colorado State Patrol to gather all of the details regarding the incident that occurred on State Highway 36 just north of Broadway. Our condolences go out to the athlete’s family and friends, whom we will continue to support.”

CSP officials said alcohol and speed are not believed to be contributing factors in the crash.

U.S. 36 north of Boulder had not been closed to vehicle traffic during Sunday’s race. That stretch of two-lane road had a shoulder blocked off with cones for cyclists and traffic realigned for the race.

Organizers of such events decide how safety barriers and road closures are configured in conjunction with the State Patrol, Reid said.

“They come up with a plan, and based on that we decide how many troopers are needed to staff the event,” Reid said. “Ultimately, we approve their plan. The expertise lies with the organizer. They do these types of things all over the country. Obviously, we have to balance the community’s needs and the safety of the participants at the same time.”

Media representatives for Ironman, which is headquartered in Tampa, Fla., didn’t respond to requests for comment Monday.

Although closing the 112-mile race course would make the event safer, it would also cause serious traffic problems for the community, Reid added.

Riders had plenty of room to stay within their designated lane, and the line separating them from vehicular traffic was heavily coned, he said.

“Why she left that area is still unknown,” Reid said.

Andrew Freeman, who participated in the race, said many of the riders were traveling outside the cones.

“I saw plenty of people riding on the wrong side of the white line or cones,” the Boulder resident said in an e-mail.

Freeman, who has participated in many bike races, said it isn’t unusual for riders to become impatient with slower riders and “cross the white line to pass.”

“At the same time, the traffic issues created by these races … can be significant and include frustrated drivers that may not be using extra caution to avoid the race participants.”

The fatal crash remains under investigation.

The Boulder Daily Camera contributed to this story.