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Traffic signal sensors

Discussion in 'Gen 2 Prius Main Forum' started by Prius Newb, Aug 20, 2014.

  1. Prius Newb

    Prius Newb Junior Member

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    After a lengthy delay of a dead 12v battery and a completely inept state government who couldn't get a copy of the title in the mail for almost 6 weeks, I finally got my 2009 Prius Touring edition out on the road.

    As I was driving home from a late(ish) night outing, about 10:45 pm, I came upon a traffic light with the in ground loop sensor. The ICE was off and I was approaching the sensor on battery power. It is my understanding that these in ground sensors detect disturbance to an electromagnetic field mostly caused by introducing some metal into the vicinity of the loop.

    I (im)patiently sat at the intersection and watched the lights cycle through twice for left turns and opposite direction traffic, but my light never changed from red to green.

    Obviously, I introduced metal into the loop's vicinity, I drove my car on top of it.

    The light never turned green, so when there was no traffic coming, I proceeded through the intersection. As soon as the ICE came on (and I assume began running the alternator/electric motor), the light turned green.

    Is this just a weird coincidence or did the alternator create a magnetic field which was detected by the in-ground loop? Has anyone else experienced this phenomenon, or was it just "one of those things". If so, are there any suggestions on how to keep from getting stuck at traffic lights?
     
    #1 Prius Newb, Aug 20, 2014
  2. xliderider

    xliderider Senior Member

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    My understanding of the traffic sensors is the same as yours, that a large enough metallic object, will be detected.

    I've turned a conventional ICE car's engine off at long traffic lights and the non running engine had no effect on the detection of my car over the sensor. I must admit that I restarted the engine before the light changed to green though.

    Are you sure you were over the detection loop? I've seen cars that were too far forward over the sensor, and too far back for the sensor to detect it.

    SCH-I535
     
    #2 xliderider, Aug 20, 2014
  3. wjtracy

    wjtracy Senior Member

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    I agree that car position seems to be the main factor.
    I do not recall any prior posts suggesting Prius itself could be an issue at traffic lights.
    The other thing I've seen is the ambulances can control the signal, but unfort our signal system doesn't handle that situation well, and keep red lights on the side streets for extended periods.
     
    #3 wjtracy, Aug 20, 2014
  4. Prius Newb

    Prius Newb Junior Member

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    Yes definitely over the loop. I am thinking/hoping that it was just a freak occurrence, but will find out tomorrow as I will be driving the same route at the same time of day.
     
    #4 Prius Newb, Aug 20, 2014
  5. xliderider

    xliderider Senior Member

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    Yes, this has happened to me several times, as I work at a major urban hospital. When the ambulance overrides the traffic signal, it can skip a cycle or two on the secondary side of the intersection to get in sync.

    SCH-I535
     
    #5 xliderider, Aug 20, 2014
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  6. wjtracy

    wjtracy Senior Member

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    ...exactly right at the hospital...sometimes you could easily get a second ambulance by the time the signals recovered from the first ambulance, and you could be there 20 minutes waiting for a green light. Seems like now the ambulances gave up trying to control the lights, and just hope they can get cooperation from the drivers.
     
    #6 wjtracy, Aug 21, 2014
  7. fuzzy1

    fuzzy1 Senior Member

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    Most of those loops are supposed to be able to detect bicycles, at least when parked at just the right spot. So they should be able to detect a parked, non-Ready Prius too.
     
    #7 fuzzy1, Aug 21, 2014
  8. Easy Rider 2

    Easy Rider 2 Senior Member

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    Over the loop or not, sometimes moving just a few inches will make a difference.
    Motorcycle riders have and even bigger problem.
    If it happens again, report it to the city or county where the signal is located.
    Your car has PLENTY of metal to trigger the inductive loop.......engine on or off.
     
    #8 Easy Rider 2, Aug 21, 2014
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  9. Prius Newb

    Prius Newb Junior Member

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    I know about the motorcycle problems first hand. I can't get out of my neighborhood's gated entry without driving on the sidewalk to bypass the swing gate.

    Drove over same sensor last night with same scenario, different results. The light did change.
     
    #9 Prius Newb, Aug 22, 2014
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