Bicyclists were twice as likely as drivers to be at fault in the nearly 2,000 collisions that killed or severely injured Bay Area bike riders in the past decade, an analysis by The Chronicle shows.

Bicycle and safety advocates say the deaths two weeks ago of two cyclists hit by a Santa Clara sheriff's deputy's cruiser should serve as a call to improve relations between cars and bikes on the roadways.

The advocates say large numbers of cyclists fail to follow the rules of the road, running stop signs and red lights, and drivers are becoming more aggressive.

"There is a juggernaut out there - the tension between the cyclists and the drivers is so high that it's become a war," said triathlon coach Marc Evans, who is starting a campaign to get the cycling community, drivers and motorcyclists to put more focus on avoiding deadly collisions on the roads.

The Chronicle's analysis of the 33,000 Bay Area collisions involving bicyclists since 1997 shows that, in the most serious accidents, the driving behaviors of bicyclists often were blamed for the crashes. Data collected by the California Highway Patrol show that bicyclists were deemed at fault in 1,165, or nearly 60 percent, of the 1,997 accidents that killed or severely injured cyclists; drivers were blamed only 520 times, or 26 percent. In most other cases, no one was listed as being at fault.

Suspicion of bias

Bicycling advocates said the statistics might in part reflect a bias among police officers, who they say often "blame the victims," especially because cyclists might not get to tell their side of the story as they are being carried off on stretchers.

"There is a prevalent perception among police officers that bikes don't belong on the road," said Leah Shahum, executive director of the San Francisco Bicycle Coalition.

Yet even the most staunch cycling advocates acknowledge that some cyclists give others a bad name by failing to obey traffic laws.

"When I see a rider run a red light, I cringe," Shahum said. "Not only is it totally unsafe, it makes me and all other cyclists look bad."

As for drivers, the data suggest their behavior is getting worse by the year.

Serious crashes

The number of serious Bay Area crashes in which cyclists were at fault has hovered at about 100 per year for the past decade, but the number in which motorists were blamed has steadily risen - from 38 in 1997 to 61 in 2006, the last full year for which data were available.

In addition, the number of accidents involving drivers hitting cyclists and then fleeing has spiked in recent years. Hit-and-run drivers killed four cyclists and severely injured 26 others in 2006 - significantly more than any other year in the past decade.

"There seems to be a natural tension between bicyclists and motorists," said Susan George, town manager of Woodside, who finds the streets in and around her hilly San Mateo County community swarming with cyclists, motorcycle riders, equestrians and drivers out for a good time on weekends and lunch hours.

Groups of dozens or even hundreds of bicyclists sometimes take over the roads, blowing through stoplights and disobeying signs, she said. At the same time, some motorists retaliate aggressively, tailgating the bicyclists, honking at them and trying to force them off the road.

"The majority of cyclists obey the rules, and the motorists, too, but then you get these outlaws," George said. "It's an ongoing battle, and in recent years the tensions have gotten worse."

Berkeley police Sgt. Mary Kusmiss said that in the past two years, her department has noticed an increase in all types of road-rage incidents.

"We get about six calls a month of road-rage cases, of people getting into screaming matches or drivers getting out of their cars and throwing their arms up," she said. "It's not just motorists and cyclists. It can be motorists and pedestrians or motorists and motorists."

Yelling at motorists

Kusmiss said the cases involving bikers can be exacerbated by the fact that in Berkeley, "some cyclists are very political about their cycling: They yell at the motorists to 'Just stop driving.' "

According to the data, when drivers were at fault in an accident, the most common type of violation cited was not giving cyclists the right of way. For bike riders, unsafe speed was the most dangerous violation, followed by riding on the wrong side of the road.

Male cyclists were almost five times more likely to be killed or severely injured than women. Fatalities and severe injury accidents affected all age groups, but riders in their 30s and 40s faired worse than others. Most common fatalities were 48-year-old males.

No one has suggested that cyclists Kristy Gough, 30, of San Leandro and Matt Peterson, 29, of San Francisco who were killed in the March 9 accident on Stevens Canyon Road in Cupertino, were at fault.

Evans, the triathlon coach who regularly trains riders in the hills of San Mateo County and was Gough's coach, said it is often the serious athletic bikers who take the most risks. He said he sees whole clubs of riders zipping through stop signs and failing to slow down.

"You get these guys who think they are Lance Armstrong or something, then they turn around and get themselves killed," Evans said.

Armstrong raised awareness about his fight against cancer with his yellow arm bracelet, and Evans hopes to start a similar bracelet campaign to promote safety among bicyclists, drivers and pedestrians.

Black-and-red armband

Evans has made the prototype of a black-and-red armband that he hopes he and others can distribute to cyclists and motorists in exchange for their promise that they will obey all traffic safety rules. George said she hopes Woodside can be a sponsor for the program.

"On the bracelets, the black is to signify our mourning for those who have been killed, and the red is to signify that you will obey all the traffic laws," said Evans, who said he believes some of the tensions on the roadway arise out of motorists' confusion about not knowing what bicyclists will do at an intersection.

"This is a huge, huge problem, and it is very out of control," he said. "What I want to do is influence cyclists, drivers and motorcyclists to obey the rules of the road."