Spend enough time on a bicycle, veteran riders say, and it's bound to happen: Out on the road one day, you'll be the target of a hurled insult or something else thrown by a passing motorist.

Or worse -- you'll be forced off the road or brushed back by an aggressive driver speeding by and laying on the horn.

"It's things that make you realize you are vulnerable," said Sarah Schroer, 41, a Santa Rosa resident and avid cyclist.

Motorists counter with their own stories, recalling bike riders who have dangerously ignored stop signs or pedestrians who have darted in front of traffic outside of crosswalks.

The often heated debate on road rules in Sonoma County has played out in public forums and polarized some camps, with cycling enthusiasts and fed-up drivers squawking about bad behavior by the other side.

The situation has been fueled by the growing number of recreational bike riders on area roads and a series of vehicle crashes in the past two years that have seriously injured or killed cyclists and pedestrians.

The county Board of Supervisors is set to wade back into the debate Tuesday by considering a proposed ordinance that would make it easier for bike riders and pedestrians to sue those who intentionally threaten and harass them.

The proposal has been advanced by bicycling advocates, with support from Supervisor Shirlee Zane.

Sonoma County would become the first county nationwide to enact such a law. Los Angeles, Berkeley, Washington, D.C., and Sunnyvale were the first cities to do so, while Sebastopol became the first local city to pass a so-called "vulnerable user" ordinance in December. The Healdsburg City Council is set to weigh a similar proposal in May.

The county proposal differs from those adopted by cities in one significant way. Where most cities entitle successful plaintiffs to triple monetary penalties -- a provision aimed at enticing attorney interest -- damages and fees under the county ordinance would be left up to the discretion of the court.

County officials said the change was needed to avoid a conflict with state law. Bicycling advocates said they accepted that analysis while voicing disappointment that it did away with a core provision.

Even so, they said the county ordinance would offer a clearer path to redress in civil court, where the standard of proof is lower than in criminal proceedings. And it would send a strong message to motorists, helping to rein in hostility toward cyclists and pedestrians.

"What it is saying is this is shared public space," said Gary Helfrich, executive director of the Sonoma County Bicycle Coalition, which has advanced the ordinance locally. "Sonoma County isn't a place where we tolerate people harassing each other on our public roads."

The ordinance also would prohibit pedestrians and cyclists from physically or verbally abusing other nonmotorized road users, Helfrich noted.

Critics have pushed back on two fronts. First, they say the proposal targets motorists for bad behavior when cyclists and pedestrians are sometimes equally to blame.

"Some of the bicyclists and pedestrians are guilty of not using good sense," Linda Berg told the Sebastopol City Council in December when its ordinance was approved. "I'm not sure putting the burden on the motorist is a good idea."

Cyclists have acknowledged that greater education is needed among their ranks to ensure traffic laws are followed. Vigilante enforcement by drivers or unprovoked aggression toward law-abiding cyclists doesn't help the situation, they say.

On the second front, critics say laws already are in place to punish those convicted of serious car-versus-bike crimes, and any ordinance targeting lesser incidents risks meddling in a murky area of law.

Advocates, though, say those cases are seldom filed, partly because there are no laws prohibiting harassment or intimidation of pedestrians or cyclists.

The county ordinance would change that for the unincorporated area, covering various cases of physical or verbal abuse where the intent is to injure a cyclist or pedestrian.

"We're not talking about name-calling here," said Helfrich, the bike coalition director.

Zane, a cyclist herself, pointed to the sport's local growth, including multiple appearances by the professional Tour of California and group rides such as Levi Leipheimer's GranFondo that draw thousands of participants to the area.

"We're all sharing the road, and anything we can do to make it safer for all of us is in our best interest," Zane said.

The impact of such ordinances is unclear. In cities where they are in place, no cases have been brought forward under the new legal protections, county officials said.

But bicycling advocates say the local laws limit the roadside confrontations that can lead to court action. They point to records maintained by the Los Angeles County Bicycle Coalition that show a drop in harassment reports made by cyclists since the city's ordinance went into effect.

"It's pushing the conversation. That's the thing we want to do more than nailing anyone in court," said Bill Oetinger, 66, ride director with the Santa Rosa Cycling Club.

Schroer, the Santa Rosa cyclist who led a pack of riders over 100 miles of local roads Sunday, said she hoped a new county ordinance would calm tensions with motorists.

"That's the main thing. I hope it would be a deterrent," she said.

The proposal requires a majority vote by the Board of Supervisors. The hearing Tuesday morning will include a staff presentation and public comment. A formal vote could follow at the board's March 19 meeting.

You can reach Staff Writer Brett Wilkison at 521-5295 or brett.wilkison@pressdemocrat.com.