Are “Speed Traps” Legal in Washington?

Posted Friday, April 6, 2018 by Andrew Charles Huff

The answer is no, speed traps are not allowed in Washington except with some limited exceptions.

But first, what exactly is a “speed trap” in our state? A “speed trap” is when law enforcement uses a pre-measured distance of roadway and then calculates the vehicle speed by using the lapsed time during which the vehicle travels between the entrance and exit of this speed trap. RCW 46.61.470 prohibits the use of these “speed traps” and only authorizes officers to determine speed by using a radar device, aircraft or the “pace” method. The “pace” method is when an officer uses their speedometer to determine a vehicles speed by traveling the same distance behind them.

RCW 46.61.470 does allow an exception to the speed trap rule…and that is the use of “aircraft.” The Washington State Patrol uses their aircraft to measure the speed of a vehicle driving between pre-measured distances on the highway. The pilot will measure how long it takes a vehicle to drive between a pre-measured distance, calculate its’ speed and then radios this information down to a trooper on the road who makes the stop.

But besides this limited use, law enforcement cannot use “speed traps” as defined to stop and ticket drivers for speeding.