If you’ve ever been pulled over for speeding, you know that your vehicle speed was likely recorded by a laser or radar Speed Measuring Device (SMD). The Washington State Patrol uses both radar and laser SMDs to enforce speed limits and keep our highways safe.
How “Speed Enforced By Radar” Really Works
RADAR stands for Radio Detection And Ranging, and is a general term for the process of determining the range, angle, or velocity of objects. Modern traffic radar uses the Doppler effect, which is an increase or decrease in the frequency of waves traveling between an observer and an object.
You’ve probably experienced the Doppler effect yourself, just in the course of everyday life. If you’ve ever heard a high-pitched ambulance siren approaching, and then it gets lower-pitched when driving away from you, you have experienced the Doppler effect.
The Doppler effect doesn’t just apply to sound. Light also travels using wavelengths. And this is how Troopers measure speed.
How do Troopers Use Radar for Speed Testing?
When measuring for speed, a Trooper will typically use an SMD to direct a beam of light toward an object. The SMD measures the time it takes for the beam to be reflected back to the device. This split-second measurement is incredibly precise, and tells the Trooper the object’s exact speed.
Law enforcement officials typically measure speed in three different scenarios: while stationary on the side of a roadway, while in a moving motor vehicle, or from an overhead aircraft.
- While stationary, if the Officer or Trooper suspects a driver is traveling faster than the posted speed limit, they will simply aim an SMD at the vehicle to detect the actual speed and confirm their suspicion.
- If an SMD is mounted in a moving motor vehicle, the device will measure the difference in speed between the moving police or patrol car and the suspect vehicle. The device will then intelligently calculate the true groundspeed of the suspect vehicle.
- Vehicle speed can also be measured and enforced by a stopwatch or GPS mapping system in overhead planes.
Accurate and Reliable – and Protecting Public Safety
Every SMD used by the Washington State Patrol is tested and certified for accuracy at least once every two years. You can learn more about the testing and certification of Speed Measuring Devices by the Washington State Patrol here.
Speed enforcement by radar is an important tool that law enforcement agencies like the Washington State Patrol use to protect drivers and keep our roadways safe and efficient. If you ever have questions about speed enforcement by radar, just ask a Trooper – we’re here to help keep you safe!