Signs reading ‘Speed Checked By Radar’ or ‘Speed Enforced by Radar’ are seen nationwide and frequently in California. As you were driving, have you ever wondered if a radar is truly tracking your speed, and if so, how it’s done? Surprisingly enough, these signs do, in fact, indicate radar speed checks, but not continuous radar tracking of every vehicle’s speed. [i] Although each vehicle’s speed is not continuously monitored, the radars refer to ‘radar guns’ used by law enforcement officers. Nordstrand Black PC describes the real meaning of these signs as,

Somewhere along that section of road, there is a spot where police officers will hide using a radar gun to monitor the speed of traffic. If officers catch someone speeding, then they can immediately pull the driver over and either issue a ticket or perform an arrest.” [ii]

Army Sgt. uses a Falcon K-band police radar gun. Photo by US Army photo/Public Domain/Wikimedia Commons

Radio Detection and Ranging (RADAR) can determine an object’s angle, range, or velocity. A traffic radar utilizes the Doppler effect. The Doppler effect is “an increase or decrease in the frequency of waves traveling between an observer and an object.” For example, the siren heard from a firetruck gets louder as it approaches and lower-pitched when driving away. [iii] The video below also details the Doppler effect and why it occurs.

In addition to speed enforced by radar signs, some signs indicate, “Speed Limit Enforced by Aircraft.”

Speed Limit Enforced by Aircraft Sign. Photo by Thatsabigif/Wikimedia Commons

In California, many of these signs are found along Interstate-5 (I-5). Surprisingly, California Highway Patrol (CHP) Golden Gate Division has an “air enforcement office” and “two small airplanes at its headquarters at Napa County Airport.” [iv] Officers identify potential speeding vehicles via radio which are “easy to see” from a helicopter hovering above. The aircraft “can quickly get the lay of the land and spot speeding cars.” The choppers have high-definition cameras but still use only their eyes to detect a speeding vehicle initially. [v]

A helicopter from the California Highway Patrol Photo by Nick Ares/Wikimedia Commons

The pilot will fly low above the car at the same speed or slower. Most freeways within the state of California have “measured and painted perpendicular white lines every mile on the side of the road.” These marks can be seen from the helicopter window and are used to calculate speed. Although CHP aircraft used to patrol “once or twice a day,” cutbacks have lessened that to “simply monitor[ing] speed while on general patrol for other things.” [vi] The CHP aircraft also does “search and rescues, pursuits, surveillance and convert into ambulances in the sky.” On Aug. 24, 2022, the CHP extended an invitation for 1,000 new officers to join their ranks, known as Air Ops. The description of the recruitment video states, “All you need is a passion to serve our communities and a commitment to provide the highest level of Safety, Service, and Security to the people of California.” [vii] The video below was released by the California Highway Patrol on Aug. 24, 2022, extending the offer for new officers to join.

References

[i] Nordstrand Black PC, How Radars Enforce Speed Limits, (2022)[ii] Id.[iii] Washington State Patrol Blog, How Does “Speed Enforced By Radar” Work? (Jul. 29, 2016)[iv] Kelly O’Mara, How Much Truth Is There to Those ‘Speed Enforced by Aircraft’ Signs? (Dec. 22, 2016)[v] Id.[vi] Jim Radcliffe, Speeders can get cited from a flying CHP officer (Nov. 12, 2021)[vii] California Highway Patrol, Join the CHP 1000 – Air Ops (Aug. 24, 2022)