When bike commuter Bill Walsh caught a cab driver making an illegal U-turn across the Pennsylvania Avenue bike lane Thursday, he figured it was just more proof of a long-running problem. Instead, the video has become a hit, earning more than 500,000 views since being posted Friday.

In the video, a cab U-turns into Walsh’s path. To Walsh’s surprise, though, an FBI car behind him turns on its siren and pulls the scofflaw driver over.

Walsh, a copy editor for the Washington Post and the author of a book on language snobbery, has had encounters with drivers making illegal U-turns on Pennsylvania before. In another video, he’s nearly hit by a driver on her cell phone.

Walsh wants a physical barrier protecting the bike lane, but worries that a cyclist will have to be hurt or killed by a U-turning driver before changes are made. “I’m afraid that might be what it takes,” Walsh says.