Ask a Cop: Is it Illegal to Warn Other Drivers of Speed Traps?

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Whether you have a question about certain laws and how they might affect you, your family or friends or how to stay safe in certain situations, we want you to ask them. Every week we will run one question and answer. To submit a question, email Shannon.burkey@patch.com.


Is it illegal to warn people of speed traps? For example, when people flash their lights to warn motorists that a police car is hiding ahead, or posting something on say Facebook with the location of the trap?


First, let's look at the legal definition of a 'speed trap' in the California Vehicle Code.

Section 40802 defines a speed trap as, "A particular section of a highway measured as to distance and with boundaries marked, designated, or otherwise determined in order that the speed of a vehicle may be calculated by securing the time it takes the vehicle to travel the known distance." Another illegal speed trap would be the use of radar or any other electronic device that measures the speed of moving objects on a roadway which has a prima facia speed limit not justified by an engineering and traffic survey within five years, or a local street or road not classified as "local" on the "California Road System Maps," or does not meet specific qualifying criteria.  

Assuming the reader is simply referring to a traffic officer conducting his or her enforcement duties, the answer is no. Our purpose for making a speed enforcement stop is simple–to get drivers to slow down. Whether they obey the speed limit due to their own good judgment, the avoidance of a citation, or your forewarning, the outcome is the same: A safer roadway.  

Recently, I heard a local radio station commenting on an officer's presence via traffic camera during a broadcast. Later, during a live interview at the same radio station, I mentioned this. I thanked the traffic announcer and explained that his warning probably helped drivers slow down and pay attention to their driving, in essence helping my fellow officer achieve his goal.  

I would caution against flashing lights at other motorists. Not only could it be distracting, but also depending on certain factors (brightness of lights versus how dark it is outside, eye health, your proximity, etc.) it could impair the vision of other drivers. Waving arms, honking, and other attention-getting behavior might also be alarming and distracting.    

Section 24409(a) states, "Whenever the driver of a vehicle approaches an oncoming vehicle within 500 feet, he shall use a distribution of light or composite beam so aimed that the glaring rays are not projected into the eyes of the oncoming driver," and (b), "Whenever the driver of a vehicle follows another vehicle within 300 feet to the rear, he shall use the lowermost distribution of light..." In other words, do not flash your high beams at other drivers.   

Regarding the use of your hazard lights, section 25268 states, "No person shall display a flashing amber warning light on a vehicle as permitted by this code except when an unusual traffic hazard exists." Since an officer conducting traffic enforcement is neither a hazard nor unusual, this section would not permit the legal use of amber warning lights.

~Sarah Jackson, Santa Cruz County California Highway Patrol

Flip October 16, 2012 at 06:20 PM
I've been driving for over 30 years, and it's always been a "known" signal that if an approaching car is flashing it's lights at me in the daytime, it's because I'm about to come up on a speed trap.
Watzon McWats October 16, 2012 at 07:47 PM
My observation has been that the use of flashing lights to warn other drivers of speed traps in our area tends to be localized and dependent on the time of day. More specifically, it seems most common on the mountain roads during commuter hours. 17, 129, HWY9, Old San Jose, etc. It's also a marginally safer way to say "move over" or "you're driving under the speed limit" in the hills without tailgating someone right off the road. Meaning sort of depends on context. I agree, it can be confusing.
Patrick Dale October 17, 2012 at 04:57 AM
Yes! I believe its old school,truckers would flash to let you know to slow down .I recently got flashed i wasn't driving but told my friend to slow down there was a cop around the bend.He thought i fooling with him but i persisted ,sure enough there was a cop waiting for us .It saved him from a ticket . By the way I am 61.
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