It all comes down to language in the State Constitution that's a throwback to centuries ago, when politicians in England would try to arrest opponents to prevent them from voting in parliament.
Washington's earliest lawmakers didn't want that happening to them, so it was written into the State Constitution and remains today.
"We interpret the Constitution to say that they can't be impeded on their way to legislative session, and so we'll follow that policy," said Washington State Patrol's spokesman Bob Calkins.
Troopers say they can't know the face of every state senator or representative, but they do let one go about five or six times a year.
"If the trooper were to learn during the course of a traffic stop that the person is a legislator, that they're on their way to legislative session, the trooper would simply get them on their way as soon as possible," Calkins said.
State Representative David Sawyer, only one year into his term, remembers hearing about the speeding privilege rule in ethics training.
"I don't think anyone would do that, because I think people would be outraged," Sawyer says. "You're not above the law, that's ridiculous."