The Accuracy of a Speed Measuring Device Must Be Proven

Posted Monday, December 5, 2016 by Andrew Charles Huff

It’s hard to be sitting in traffic court for long and not hear the case of Seattle V. Peterson referenced by either attorneys or judges. This case provides the framework for the use of speed measuring devices (radar guns) in court and essentially requires that the accuracy of these devices be proven.

On March 1, 1982, Seattle Police Officer Thomas Byers was on routine patrol when he observed a car that appeared to be speeding. Using his radar device, he determined Mr. Peterson was speeding and issued him a citation. Mr. Peterson decided to challenge the ticket and requested a Contested Hearing.

At the hearing, the only evidence of speed was Officer Byers’ testimony that, before he locked in a reading on the radar unit, it appeared to him from visual observation that Peterson’s vehicle was traveling between 40 and 45 m.p.h. The court found the infraction committed.

But on appeal, the issue was whether the particular machine (SMD) itself was proven to be reliable. The court found that if the validity of a scientific principle (the Doppler effect) is a prerequisite to its admission into evidence, then the accuracy of the actual device must also be proven before the results can be admitted into evidence.

Here, the only evidence offered regarding the radar unit was the testimony of Officer Byers, who candidly acknowledged that his information about the radar device was limited to instructions on how to calibrate and operate it. No evidence was offered relating to the design and construction of the radar unit. The only evidence on the accuracy of the radar unit was the opinion of Officer Byers that he had confidence in the accuracy of the unit.

Seattle v. Peterson, 1985