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  1. #1
    Senior Member nostalgic's Avatar
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    Triggering Stoplights

    This topic has been visited before, but I couldn't find the thread, so here we go again.

    On my way to the university, there are two major intersections I have to cross. The first one has a stoplight that either seems fairly easy to trigger, or is set to change no matter the traffic density, but not the second. I remember reading that there is a way to trigger stoplights without the help of cars and without pushing the pedestrians' walk button, but cannot remember what that is.

    Correct me if I'm wrong, but is there a way?

  2. #2
    mosquito rancher adamrice's Avatar
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    If you can't trigger the light, treat it as broken and ride through when safe.

    Sometimes people with steel bikes can trigger some balky sensors by laying their bikes down directly over the cuts in the pavement

  3. #3
    Senior Member Grishnak's Avatar
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    On the instructables site,is a how to trigger the lights article.I think they used a neodymium magnet.

  4. #4
    Senior Member nostalgic's Avatar
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    Thanks.

    Do neodymium magnets need to be as close to the ground as possible, or can they be placed elsewhere, such as in your front or rear basket?

  5. #5
    Senior Member Spudd's Avatar
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    I don't know if the magnet thing works, but if it does, I would think it would need to be as close to the ground as possible. Here in Toronto they're starting to paint dots on the ground that indicate where you need to place your bike to trigger the light, which is nice.

  6. #6
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    Most traffic sensors (at least in the US) are induction-loop types that work the same as the metal detector devices people use at the beach to find coins and jewelry. They use a high frequency electric current in loops just under the pavement. Any nearby metal absorbs some of the energy of the resulting field and this is what triggers the light. No need for any of the metal to be iron or steel, so a bicycle with aluminum rims should be detectable. *BUT* this depends on how high the sensitivity is set on the detector. Many cities just set them high enough to detect cars and trucks which causes problems for cyclists (and some motorcyclists as well).

    First make sure you're positioning your bike directly over the sensor location. If the pavement cuts are visible then place your wheel directly over the middle cut (or along an edge is it's a single loop pattern). Hidden loops after a repaving make it more difficult, but the loop is usually directly behind the stop line and in the middle of the lane. If it still doesn't respond then treat it as a broken signal (i.e. proceed when safe after being at a full stop) and contact your local transportation department with a request to adjust the sensor for higher sensitivity. In our area they will come out quite promptly to readjust sensors

  7. #7
    Senior Member Shimagnolo's Avatar
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  8. #8
    Stealing Spokes since 82' Fizzaly's Avatar
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    Quote Originally Posted by prathmann View Post
    Most traffic sensors (at least in the US) are induction-loop types that work the same as the metal detector devices people use at the beach to find coins and jewelry. They use a high frequency electric current in loops just under the pavement. Any nearby metal absorbs some of the energy of the resulting field and this is what triggers the light. No need for any of the metal to be iron or steel, so a bicycle with aluminum rims should be detectable. *BUT* this depends on how high the sensitivity is set on the detector. Many cities just set them high enough to detect cars and trucks which causes problems for cyclists (and some motorcyclists as well).

    First make sure you're positioning your bike directly over the sensor location. If the pavement cuts are visible then place your wheel directly over the middle cut (or along an edge is it's a single loop pattern). Hidden loops after a repaving make it more difficult, but the loop is usually directly behind the stop line and in the middle of the lane. If it still doesn't respond then treat it as a broken signal (i.e. proceed when safe after being at a full stop) and contact your local transportation department with a request to adjust the sensor for higher sensitivity. In our area they will come out quite promptly to readjust sensors
    +1 Im pretty sure the sensors are the same as my company uses in parking garages and they are exactly as you described, I personally have found using the corners to be the best method of getting them to trip.

  9. #9
    Senior Member mikeybikes's Avatar
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    If you're not able to trigger it after trying suggestions, contact the local dept of transportation and ask them to calibrate it. I've been successful in getting a dozen or so calibrated. The only one that was never calibrated was torn down two weeks after I called. So, go figure.
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  10. #10
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    Quote Originally Posted by Fizzaly View Post
    +1 Im pretty sure the sensors are the same as my company uses in parking garages and they are exactly as you described, I personally have found using the corners to be the best method of getting them to trip.
    +1 I am an electrical engineer, and prathmann gave a very good description of how most of the detectors work. They are most sensitive to loops of conductive material, and bicycle rims are usually the best things to trigger them. Place your wheel along the line of the pavement cut to get maximum results. If you have a carbon fiber bike, with carbon rims (you need to get your head examined), but one trick that you can use is to put a loop or two of copper wire or tape inside the tire, under the tube.

    Random thought - how many Car-Free folk ride carbon fiber bikes?

  11. #11
    Wookie Fred chewybrian's Avatar
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    What I want to know is, what is the signal to the driver behind me, to please pull up to trigger the light? The one light that gives me trouble is on my afternoon commute, in heavy traffic, and will not trip for me. I can pull up far enough that the car behind *could* trigger the light. But, whatever signals I give, pointing to the ground, and then the light, I get only blank stares from the confused motorist behind me.

    Many times, a right on red is just as easy, depending on your heading, and that's my usual answer. But, in that case, it would mean a long run the wrong way, or a u-turn in crazy traffic.
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  12. #12
    Stealing Spokes since 82' Fizzaly's Avatar
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    There are a few in my area that don't have signals, they are on timers but in boise cyclists only have to come to a stop and can proceed through (if clear that is) so in my morning rides (5:30am) i generally come to a rolling stop anyways as there usually isn't any cars to be seen.

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    Quote Originally Posted by chewybrian View Post
    What I want to know is, what is the signal to the driver behind me, to please pull up to trigger the light?
    I have a lot of cars that stop about 2 car lengths BEHIND me at lights like this. O_o I usually just motion them forward with a big smile, and then point to the ground and the light. Sometimes when I motion them forward, they just look confused. I just smile & nod and keep motioning. Then they usually move up.

    Sometimes if they look friendly & I feel chatty, I'll tell them about tripping the light signal.

    I only have one light on my regular routes that I can trip with any regularity all by myself.

  14. #14
    In the right lane gerv's Avatar
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    Thanks for these links.

    The second link summarizes the issue pretty well. There are 3 types of sensor. The most common in my city is the inductive loop sensor. You need to get your wheel to cover as much of it as you possibly can. Normally here the sensors are shaped as hexagons, but the technique is the same... shoot for a section and cover as much as you can.

    One thing to note is that, depending on the sensitivity of the light, it may never trigger without a 3000 lb can on top of it. Motorcycles will be left idling at the light, as well as bicycles.

    In that case, consider calling your city and telling them you'll be soon forced to run red lights. Don't get off the bike and trigger the walk button... this makes it difficult and even dangerous to get back in the lane. Instead, tell your city to get it fixed for you.

  15. #15
    Senior Member wahoonc's Avatar
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    Quote Originally Posted by gerv View Post
    Thanks for these links.

    The second link summarizes the issue pretty well. There are 3 types of sensor. The most common in my city is the inductive loop sensor. You need to get your wheel to cover as much of it as you possibly can. Normally here the sensors are shaped as hexagons, but the technique is the same... shoot for a section and cover as much as you can.

    One thing to note is that, depending on the sensitivity of the light, it may never trigger without a 3000 lb can on top of it. Motorcycles will be left idling at the light, as well as bicycles.

    In that case, consider calling your city and telling them you'll be soon forced to run red lights. Don't get off the bike and trigger the walk button... this makes it difficult and even dangerous to get back in the lane. Instead, tell your city to get it fixed for you.
    I have been in some places where the walk lights didn't work either.

    If I cannot trigger the light in one cycle I will ride through it and report it.

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  16. #16
    Senior Member Shimagnolo's Avatar
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    Quote Originally Posted by wahoonc View Post
    I have been in some places where the walk lights didn't work either.
    aka the "placebo button".
    I have even encountered a light that had the button programmed as a placebo button during the day, but if pressed before 6am it gave an immediate green light.

  17. #17
    bragi bragi's Avatar
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    The city of Seattle has been nice enough to paint a little "T" over the spot that is most likely to trigger a traffic light at many intersections. I've noticed that my wheels don't trigger the signal nearly as effectively as my bottom bracket; but then, I ride a fairly heavy steel touring bike. At intersections that don't seem to work with bicycles, I either treat it like a malfunctioning signal and run the light if traffic is sparse, or use the pedestrian signal.

    But honestly, unless it's very late at night, there is enough car traffic in the city that I don't need to worry about tripping signals; there's usually a huge massive car or SUV around to do it for me.
    If you're not part of the solution, you're part of the precipitate.

  18. #18
    Sophomoric Member Roody's Avatar
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    My problem is that I'm too impatient. I'll wait about 15 seconds over the loop, then figure it's broken and run the light. Then I'll look back over my shoulder and see that it's already green.


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