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  • RADAR and side mirrors?

    I was wondering if any LEOs had anyone contest a citiation and was using a side mirror to calculate speed using the RADAR gun. If so how did that hold up in court?

  • #2
    Radar

    I constantly use my radar gun on my side mirror when parked on the side of the street. We are required to submit a PC affidavit for the citation (as if the front of the citation isn't good enough!). What I write on my affidvit is that said vehicle operated by said individual was clocked on radar speeding ??mph in a posted ??mph zone. Also if they do continue speeding I'll use my left hand and hang the radar (hand held) out the window and clock that way just to make sure.

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    • #3
      I've been told you wouldn't be able to because you wouldn't have PC. Its not hard if they are doing 35 in 15. I've never had anyone contest just wanted to know for future refrence if it did ever come up.

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      • #4
        I'm assuming you're speaking of looking into your mirrors to obtain a visual estimation of speed. If so, I do this quite often. I don't make it a habit of stating "I observed a vehicle travelling at a high rate of speed in my rearview mirror..." Don't give the defense any more than necessary. If asked which way you were parked and direction of travel, etc. then obviously it's going to come out that you were estimating speed in your mirror. You'll just have to articulate how every driver on the road estimates speed in their mirrors when changing lanes, merging into traffic, etc.

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        • #5
          We have rear-facing radar antennas and I frequently estimate the speed of vehicles approaching from behind me using the rearview mirror. It's really no more difficult than estimating the speed of a vehicle approaching you from the front...just takes a little practice.
          "He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you."
          -Friedrich Nietzsche

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          • #6
            I remember this topic coming up in my radar class.

            If you're talking about estimating speed using a mirror, the instructor advised against it. His contention was that a mirror, whether sideview or rearview, allows only a limited field of vision and therefore could be contested as inadequate to make a proper visual estimate. Of course, those of us who've run radar on a few thousand cars over the years know that we could estimate the speed of a car using a dental mirror if we had to. But I'm not going to specifically document the mirror's use in my report. If the attorney is good enough to bring it up and argue the point, kudos to him/her. May as well make them earn their $200/hr.

            If you're talking about bouncing the radar signal off a mirror to get a 'confirmation of your visual estimate', we were told that would not hold up very well in court. According to our instructor, there are too many factors that can impact the radar reading (is the mirror flat/concave/convex?, how dirty is the mirror?, are your sure your radar wasn't acquiring another vehicle out of your mirror's limited field of view?, etc.). If someone has a better grasp on the physics involved wants to argue that point, I'd be glad to hear it.

            Now that our vehicles have front- and rear-facing radar, it's not much of an issue for me anymore. As long as I can hit the button to switch it, I'm good.

            Here's one thing I discovered, though. We have a notorious stretch of roadway that's very narrow, hilly, sharply curved and hemmed in by trees. Traffic volume at certain times of day is fairly heavy for a quiet residential street. I've found a spot where I can sit with a hill behind me and a stop sign, then a straighter stretch of roadway in front of me. I can sit in this location with just the front radar on and be alerted to speeders from either direction (many times I'm completing paperwork while listening to the radar's audio signal to catch my attention; then I make my visual estimate and confirmation). The front-facing radar works normally for the vehicles coming at me. But the stop sign works like a mirror and bounces the signal to the hill behind me. That way I hear if a car's approaching from the rear. Once alerted, I make my visual estimate and flip to the rear-facing radar to get my official confirmation.
            Caution and worry never accomplished anything.

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            • #7
              Originally posted by kirch
              If you're talking about bouncing the radar signal off a mirror to get a 'confirmation of your visual estimate', we were told that would not hold up very well in court. According to our instructor, there are too many factors that can impact the radar reading (is the mirror flat/concave/convex?, how dirty is the mirror?, are your sure your radar wasn't acquiring another vehicle out of your mirror's limited field of view?, etc.). If someone has a better grasp on the physics involved wants to argue that point, I'd be glad to hear it.
              we all know the beam travels at 186,000miles per second and a little bit of dirt isnt going to change that, its a constant... its not going to have any major effects, however the angle of the mirror can have an effect on angular cosine... but thats actually taking the violators speed down a few mph... so it benifets the violator if anything, you can argue that in court... i mean if it were up to me, i wouldnt do the "bounce off the mirror" trick just because a wannabe "know it all" attorny is going to attack that mess like crazy acting like he knows what he's talking about and what not... rather not deal with it... with the amount of speeders on the roadways, its better to just do it by the book so you wont run into any ruts in court.
              Last edited by VAsteve20; 03-04-2006, 09:34 AM.

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              • #8
                I'm a RADAR/LIDAR master instructer and I know your not supposed to bounce the signal off the side mirror but the speeding on this roadway is bad. On a normal basis I would not recomend this or do it myself. This is the only way I can get a clear shot with out impeading the flow of traffic. I may do this once or twice a week and it has been effective in the speed control here. I guess word travels fast here.

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                • #9
                  The instructor of my radar class also advised against bouncing off of the mirror. Instead I will sometimes park parallel to flow of traffic and hang my radar gun backwards out the window and watch the approaching traffic and the readout in the mirror. You quickly adapt to reading the radar gun backwards. I only do this on narrow streets where the narrower field of view in the mirror does not impede my ability to see approaching traffic.
                  If you see me running try to keep up!

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                  • #10
                    Originally posted by LeeRoy
                    Instead I will sometimes park parallel to flow of traffic and hang my radar gun backwards out the window and watch the approaching traffic and the readout in the mirror.
                    I do this when I can but more times than not I will have a vehicle parallel parked behind me.

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                    • #11
                      Originally posted by VAsteve20
                      we all know the beam travels at 186,000miles per second and a little bit of dirt isnt going to change that, its a constant... its not going to have any major effects, however the angle of the mirror can have an effect on angular cosine... but thats actually taking the violators speed down a few mph... so it benifets the violator if anything, you can argue that in court... i mean if it were up to me, i wouldnt do the "bounce off the mirror" trick just because a wannabe "know it all" attorny is going to attack that mess like crazy acting like he knows what he's talking about and what not... rather not deal with it... with the amount of speeders on the roadways, its better to just do it by the book so you wont run into any ruts in court.
                      LIDAR beams travel at 186,000 miles a second, RADAR is only travelling at 760 MPH.

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                      • #12
                        Originally posted by SWH
                        LIDAR beams travel at 186,000 miles a second, RADAR is only travelling at 760 MPH.
                        SONAR (sound waves) travels at 760mph in air at sea level, RADAR is based on radio waves, which, like LIDAR and the rest of the EM spectrum, travel at the speed of light in a vacuum.

                        Edit: On a side note, dirt may scatter the radio wave so it might not be pointed at what you might be pointing the gun at, although I doubt it. Given the wavelength of radio waves even a sheet of rusted metal would look like a perfect mirror to a radar gun.
                        Last edited by Dolmen; 03-04-2006, 06:12 PM.
                        Mankind shall not be free until the last king is strangled with the entrails of the last priest.

                        Dithyrambe Sur La Fête Des Rois -- Denis Diderot (1713 - 1784)

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                        • #13
                          Originally posted by Dolmen
                          SONAR (sound waves) travels at 760mph in air at sea level....

                          Great idea! Let's start using SONAR to measure vehicles speeds. Instead of a radar detector, you could roll down your window and listen for the {{{PING!!!!}}} sound coming from the parked squad car.


                          Instead of using a rear-view mirror for radar, every cruiser would just have a large periscope for when they were parked behind a small hill.

                          Sorry......I just could not resist throwing that one in there.

                          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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                          • #14
                            Originally posted by SWH
                            LIDAR beams travel at 186,000 miles a second, RADAR is only travelling at 760 MPH.
                            lol alright...
                            sure thing... when i went through radar school, i was taught the beam travels at 186k mps...

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