In a city coping with an affordability crisis and growing homeless problem, it may seem surprising that one of the most heated political battles of the year centers on how bicyclists stop at stop signs.

Supervisor John Avalos’ proposed ordinance allowing bicyclists to roll through stop signs — instead of coming to a full stop — has generated a mass petition drive by the San Francisco Bicycle Coalition to support it and a rare veto threat by Mayor Ed Lee.

The Board of Supervisors is expected to vote on the legislation Tuesday, and it is still two votes short of the eight needed to override that veto.

“Given that stop signs are there for a reason and people have gotten killed at intersections, it’s not trivial,” said John J. Pitney Jr., a professor of politics at Claremont McKenna College. “Maybe not the most important issue, but it does have significance.”

The legislation has also generated an almost philosophical debate about who is squandering more time: the police who are ticketing bicyclists, the supervisors who are trying to legislate bike traffic laws, or the mayor who is expending political will by threatening a veto.

All sides are digging in.

The police continue to give out tickets to bicyclists along the popular Wiggle route between Market Street and the Panhandle. This month, Katrina Sostek got a ticket on her way to work for running — or rolling — through a stop sign in Duboce Triangle. The officer marked Sostek’s speed on the ticket as less than 5 mph.

“It wasn’t an unsafe situation. I wasn’t endangering anyone. And this police officer took 15 minutes to give me a ticket. She could have been doing something worthwhile during that time,” Sostek said. “I do see unsafe things every day and they are rarely ticketed, but my failure to come to zero miles an hour and only 3 miles an hour lands me with a $200 ticket.”

Strong support, opposition

Judging by petition signatures, stories like Sostek’s have made getting the ordinance passed the second most popular campaign in the 40-year history of the San Francisco Bicycle Coalition, said spokesman Chris Cassidy. The most popular was its opposition to a proposal to charge pedestrians and bicyclists for crossing the Golden Gate Bridge.

Back to Gallery Passions in overdrive on plan to allow rolling stops for... 5 1 of 5 Photo: Liz Hafalia, The Chronicle 2 of 5 Photo: Liz Hafalia, The Chronicle 3 of 5 Photo: Paul Chinn, The Chronicle 4 of 5 Photo: Paul Chinn, The Chronicle 5 of 5 Photo: Paul Chinn, The Chronicle









Opposing the legislation are the mayor, the Mayor’s Office on Disability, the Department of Public Health, the Police Department, the Municipal Transportation Agency and some pedestrian safety advocates.

In a Dec. 4 letter to the supervisors’ Land Use Committee, Police Chief Greg Suhr released collision numbers involving bicyclists and cars for the first nine months of 2015. It showed 447 collisions, with bicyclists at fault 46 percent of the time. Two bicyclists died.

“It is unacceptable to encourage someone to break a law that could result in injury or death because it is ‘inconvenient’ for the driver/bicyclist to come to a complete stop,” Suhr wrote.

Critics countered that the statistics are incomplete and don’t detail the behaviors that led to the collisions.

“If you are talking about ticketing people who are slowly and cautiously going through an intersection, that is not putting anyone in danger,” Supervisor Scott Wiener said at the Land Use Committee hearing.

“Our limited police resources should be used for more important things,” Supervisor London Breed added. “I am hopeful we can get this legislation passed and we can deal with a lot more pressing issues in this city around public safety.”

Speculation on impact

With just one study done on the impact of the rolling stop — in 2010, on an Idaho law — there are little hard data to back up either side’s contention that the ordinance would improve or harm safety on the streets. Only Idaho and a few Colorado counties permit the rolling stop.

That leaves both sides speculating on the impact.

“I fear the passage of this ordinance will come at a high cost to pedestrians, disabled people and seniors,” Supervisor Malia Cohen said at the hearing. Cohen said she would be open to a pilot program.

The legislation would make ticketing bicyclists who roll through stop signs the lowest priority for San Francisco police. It would permit bicyclists to treat a stop sign as a yield sign and ride through without stopping, at a speed 6 mph or less, if they decide it is safe. The police could still do targeted enforcement of bicyclists who don’t yield safely.

Farrell, Peskin undecided

So far, it has the support of six supervisors: Avalos, Wiener, Breed, Eric Mar, David Campos and Jane Kim. Supervisors Cohen, Norman Yee and Katy Tang are expected to vote against it. That means that to override the mayor’s veto, Supervisors Mark Farrell and Aaron Peskin would need to vote for it.

Farrell said he hasn’t made up his mind, while Peskin — who joined the board last week after winning the November election — seemed baffled by the legislation when asked about it. “I’m focused on writing a resolution to extend rent control,” he said. “That’s what I’m thinking about.”

Peskin suggested he wants to see the mayor follow through on his threat to veto the legislation before he gives serious thought about whether to support it.

“Let’s talk about it after then,” Peskin said.

Which means Round 2 of bike yield legislation could still be forthcoming.

Emily Green is a San Francisco Chronicle staff writer. E-mail: egreen@sfchronicle.com

Twitter: @emilytgreen