On a cold afternoon last December, Brion Barnett was riding his Univega bicycle home along a two-lane, tree-lined street off Southwest Scholls Ferry Road in Beaverton, where he works as a city engineer.

Dusk was approaching. Barnett’s tail light blinked as he pedaled along at about 24 mph. A few cars passed, taking care to give him room. As he approached an intersection, he heard another car approaching from behind.

It was a silver BMW. As it passed—very slowly—the passenger-side mirror struck Barnett’s elbow. “It scared the bejeezus out of me, but there was no actual physical damage,” Barnett says. “I’m lit up like a Christmas tree, so for him to not see me, I find it hard to believe.”

There were no witnesses. But the driver later told police that he had “noticed traffic backed up due to a lone bicyclist riding out in the roadway.”

Barnett memorized the BMW’s license plate number. The next day, he called Portland’s most prominent “bike lawyer,” Ray Thomas, and asked what could be done.

Most bad roadside encounters either pass without consequence or escalate into road rage. But Thomas educated Barnett about a state law so obscure many cops don’t know it exists—Oregon Revised Statute 153.058, “Initiation of violation proceeding by private party.” Write that down. You might want to use it.

“It’s the only statute I’m aware of, in any state, that allows a citizen to become a traffic cop,” says Thomas. “It can be used by a driver against a cyclist, a cyclist against a driver, in boating cases, in hunting cases—it really levels the playing field.”

Thomas figured the driver could be cited for “unsafe passing on the left.” So Barnett made an appointment with the Washington County Sheriff’s Office, filed a written complaint against the BMW’s owner, Eric Janoe, and asked that he be served with a citation. The police were required to follow up. Five months and one court appearance later, Janoe was fined $242. Barnett says he wanted the driver to know that “there’s room in the road to share. It wasn’t to be an A-hole and say, ‘Hey hey, you got a $240 ticket.’”

Another Thomas client, Jeff Mandel, used the DIY ticket law against the driver who hit his wife, Yifang Qian, as she walked across West Burnside Street. In July, a judge found 73-year-old Duck Soon Paik guilty of failure to stop for a pedestrian, but not guilty of careless driving. Her ticket came to $209. “I think if we did it again, we probably would’ve got her on both counts,” Mandel says.

Just got swiped?

Write down everything you remember. You have six months to issue a citation. Download Thomas’ how-to guide. Read it.

Also download an Oregon Uniform Traffic Citation form. If there was an accident, call the police officer who responded. Otherwise call the police non-emergency line, 823-3333. Tell them what you want to do. “Many times…they don’t know what the hell you’re talking about,” Thomas says.

Persevere. Once you find a helpful officer, they’ll have you swear to a summary complaint. (Don’t lie.) Then out goes a summons. Eventually, a court date will be set. (Don’t miss it.)