It had happened just, once too often.

Rebecca Mead is a bicycle commuter, and up with determined cheerfulness the daily outrages of automobile traffic - the lunging buses, the cars that don't signal, the taxis and bread trucks that seem ready to dive over a biker's back without so much as changing gears.

Then on May 23, Mead was making her way down Courthouse Road in Arlington, en route to her job as an education specialist at the Smithsonian Natural History Museum. She had waited at the light at 15th Street and then bicycled out - ahead of traffic, as she tells it - when a white Chrysler suddenly sped by to her left and swung into a right turn directly in front of her bicycle.

"I slammed on my brakes and skidded into the curb," Mead said a few days ago.

Neither she nor the bicycle was badly banged up, but Mead was furious. This was her regular commute route. She and the Chryler might tangle like this every morning. And what was it with these drivers, anyway?

Mead got back on her bicycle and followed the Chrysler into the parking lot where it had stopped. She and the driver, a lawyer named J. Walter Newlon, had words. Yes, he had seen her, Newlon said, but he had his turn signal on and that was that. He went off to work.

Mead marched over to the court-house. She reported the whole business to the police, and the police, to her surprise, issued a summons ordering Newlon to traffic court.

The charge was reckless driving, later amended to failure to yield right of way. And the assistant commonwealth's attorney handling the case, through some small cosmic fluke, had bicycled his way through law school.

"We have a lot of empathy for bikers," said the prosecutor, Kenneth Melson.

Newlon pleaded guilty and was charged for court costs - $18.

"A very nice fine," Mead said afterward, sounding satisfied. "All I was really looking for was some kind of minimum fine." And court costs, she said, would do.

Newlon said he was not particularly upset by the whole business.

"She was in back of me," he said. "I could see her in the mirror. If I'd have stopped, she'd have crashed into the rear of the car and broken her neck."

Why did he turn in front of her without letting her pass by?

"She didn't have the bicycle under control, that was all that was," Newlon said.

Mead is mollified and figures it's one point for the bikers in what sometimes seems fike a badly stacked game.

"I was outraged because he cut me off," she said. "I was even more outraged because he was so obnoxious about it. He never even apologized. I just wanted it formally brought to his attention, in hislanguage, that I had priveleges - and I did."