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  • Question about speed gun

    Is it possible for an officer to get a speed on a car that is going towards the officer and the officer is driving himself? So both cars are moving towards each other. Thanks

  • #2

    Yes, it is known as "moving radar" and works quite well.


    The radar unit takes the closing speed (the patrol car moving towards the target vehicle) and automatically subtracts the police vehicle's velocity - giving a reading of the target. This, of course, requires a certifed calibration on both the patrol car's speedometer and the radar unit; and the officer must ensure that the "patrol" speed indicated on the radar gun is the same as on the speedometer of the car.

    If the cop is going 60 and the violator is doing 70, the "closing" speed will be 130 mph; but the radar gun should show "70" in the target window display and "60" in the one for the patrol car. If the radar gun should get a 'ghost' signal (a slow-moving truck's rear surface, etc.), it may show the "patrol" speed as being too slow - thus making oncoming traffic appear 'faster' to the radar gun.

    You can read a lot more about this and I have over-simplified it, but radar is very accurate under proper conditions and when operated by a trained officer.

    Oh, some of the newer radar guns also have "same direction" capability where the officer/deputy can measure & confirm your speed while you are moving away from him or he is approaching you from behind.

    With the old-school Kustom Signals units we had, they only worked if you were coming towards the antenna; but (as mentioned above) our troopers here in VA have the newer, better ones that do just about everything except prepare dinner.


    The comments above reflect my personal opinion as a private citizen, ordinary motorist and all-around good guy.

    The aforementioned advice should not be construed to represent any type of professional opinion, legal counsel or other type of instruction with regard to traffic laws, judicial proceedings or official agency policy.

    ------------------------------------------------

    "Ignorance on fire is hotter than knowledge on ice."

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    • #3
      Originally posted by Euro_Autobahn View Post
      Is it possible for an officer to get a speed on a car that is going towards the officer and the officer is driving himself? So both cars are moving towards each other. Thanks
      Yep
      "Would I ever leave this company? Look, I'm all about loyalty. In fact, I feel like part of what I'm being paid for here is my loyalty. But if there were somewhere else that valued loyalty more highly, I'm going wherever they value loyalty the most. " --Dwight K Schrute (The Office)

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      • #4
        Thanks for the explanation.

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        • #5
          Get that all the time. How can you clock me when your moving? It's magic they taught us in speed trap school haha. We don't have the same direction moving radar but it's ok most people seem not to speed up in front of me.
          Where'd you learn that, Cheech? Drug school?

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          • #6
            Actually I have two more questions.
            1. Lets say an officer is using moving radar while he is following a car in front of him and the road starts to turn so the car that he was following disappears while another one comes into the radars view. Except, now the car that comes into view is coming towards the officer and not away like the other car. Can the radar suddenly change and show a speed for the new car that is now coming towards the officer.

            2. If yes, would the speed be correct since now the car is heading towards the officer? What I mean by this is does the officer have to switch something on the radar to get an accurate reading from a car that he is following to a car that is heading towards him? Or the does the radar automatically take that into effect being able to tell the difference?

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            • #7
              The radars that my department uses will not allow me to be moving AND register a speed for a vehicle that is IN FRONT of me and MOVING IN THE SAME DIRECTION. In other words if I am going Northbound and have a vehicle in front of me also going Northbound, I will not be able to get a radar reading, I could "pace" that vehicle though.

              In answer to your second question, yes radars in continuous use can provide an automatic different reading once a vehicle leaves the "view" of the radar and another enters into the view. This can be done without turning off or "resetting" the unit.

              As always, departments use different units, this is just typical for the unit used in my squad.
              The above comments reflect the personal, off-the-record, unofficial opinions of the individual posting them only, and in no way, shape, or form should be taken to indicate any particular opinion, policy, or belief by the poster's or any other agency, governmental entity, organization, or corporation. Thank you and have a nice day.

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              • #8
                Yes. My last Stalker could do stationary, moving, and moving in same direction.

                NONE COULD ESCAPE ME!!!
                Airborne Cops are closer to God.
                Arms and legs are just extensions of flight controls.

                THESE BIG RED LETTERS HELP ME FIND MY POST.

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                • #9
                  As answered to your second question, yes the radar will recognize the change and display the speed of the new target, even coming from the opposite direction. (The "doppler tone" would change)

                  There is not simply enough space on an internet forun to explain all of the complexities of police radar and training. In Florida RADAR training is a 40 hour course solely based on the theory, operation, history, types of errors, and other information. In addition officers (again in Florida)are required to successfully estimate the speeds of passing cars (within 3 mph) of 100 cars (50 while driving, and 50 while stationary). There really is more to just turning on the Radar.

                  Some RADAR's are also equipped with a second antennea that monitors traffic behind the police car. It is especially useful obtaining the speeds of cars as they come up behind me.

                  As mentioned RADAR used by a trained operator is difficult to beat.

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                  • #10
                    Originally posted by Euro_Autobahn View Post
                    Actually I have two more questions.
                    1. Lets say an officer is using moving radar while he is following a car in front of him and the road starts to turn so the car that he was following disappears while another one comes into the radars view. Except, now the car that comes into view is coming towards the officer and not away like the other car. Can the radar suddenly change and show a speed for the new car that is now coming towards the officer.
                    My Kustom Signals Golden Eagle will do both same direction and opposite direction RADAR; however, it will not do them simultaneously. It must manually be switched into one mode or the other. If I were getting a reading on the car in front for some reason, then it disappeared and I wanted to get a reading on a car approaching I'd have to change modes, but it would give me a speed almost instantaneously.

                    I believe there is a new RADAR that does both same and opposite direction moving RADAR, as well as approaching and receding simultaneously. It uses both heads at the same time to provide front and rear readings in both mids. No more need to switch manually, the unit will display both automatically.

                    2. If yes, would the speed be correct since now the car is heading towards the officer? What I mean by this is does the officer have to switch something on the radar to get an accurate reading from a car that he is following to a car that is heading towards him? Or the does the radar automatically take that into effect being able to tell the difference?
                    Yes, if he's not using that new RADAR he'd have to switch modes to get a reading. Contrary to what you may think though any cops don't simply driving around checking every car they can. If he was behind a car there'd be no need to check his speed with the RADAR since he'd already know that cars speed because he'd be keeping pace with him, thus the RADAR would most likely be in opposite direction mode anyway.

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                    • #11
                      Thanks for the replies.

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