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Triggering Traffic Lights

Discussion in 'General Motorcycling Discussion' at netrider.net.au started by DKEL, Mar 18, 2006.

  1. For those that dont know, in summary, Many traffic lights work by the presence of an induction loop underneath the road. A large mass of metal (a car) triggers the loop and the lights soon go green (hopefully).
    Of course our problem is that sometimes bikes are not big enough to trigger the lights.
    There have been other posts about getting off and pressing the pedestrian buttons, going through red etc.
    Question for comment:
    Are Rare Earth Magnets place don the bike any good for the purpose of triggering traffic signals?

  2. Not sure about the rare earth magnets. If they affect the inuctance of the loop then they would assist.

    The primary reasons for the loops not sensing the presence of a vehicle is because the vehicle has failed to alter the inductance sufficiently. This can be due to:

    * Vehicle has low ferrous content (IRON / STEEL). If your bike (Or car for that matter) has alloy wheels, alloy engine, alloy frame, belt drive etc, but very little steel, then sorry, it isn't going to trigger the sensors.

    * Vehicle has too much ground clearance. Many large trucks and buses don't trigger the sensors because the ground clearance means the iron / steel is too far above the loop. This coupled with alloy wheels on most new trucks means they have the same problem as a lot of bikes.

    * Loop sensitivity set too low. Sensor fails to works simply because it has not been set correctly.

    If you know of an intersection where the sensors do not appear to work for you, take a note of the location and ring the number on the cabinet (It's different in each state and in Brisbane there two different ones - on for Main Roads and one for Brisbane City Council). Tell whoever answers the problem, making sure that you give the lane, direction and the fact that you are on a motorbike. They won't attend the intersection immediately, however they will check the sensitivity of the loops and adjust accordingly, sometimes calling you back to see if the problem still exists.
  3. Wow Auscruiser!That was very comprehensive!

    I remeber reading in AMCN a few years ago about this


    The green light trigger. If you seem to have problems with triggering lights everywhere it might be worth getting one of these.
  4. Somebody told me that clicking the starter motor on briefly, as it's electric, can help trigger the sensors...

    I dunno.
  5. Another thread got derailed onto this topic not long ago. Vic suggested putting the side stand down directly over the sensor (remembering to put the bike in neutral of course :wink:). Tried it on a few problem intersections tonight and it does actually work - no more running red arrows for me :grin:.
  6. Three main things affect the sensitivity of the coil.

    Material distance from the coil.

    Material Conductivity

    Material Permability

    Now, most alloys used on new bikes have low conductivity, ie Al (25-50%IACS) (note: steel is heaps lower about 1-10% depending on alloying, but has a large effect due to permability- ability to be magnatised)

    By adding a small rare earth magnet, you get a large increase in the permability, there for creating a greater change in inductance in the coil.

    If you put the magnet close to the end of your stand, it will get closer to the coil (when stand is lowered) giving it a greater effect on the coil.

    Trigging the started moter may effect the coil as a selenoid is activated which is esentialy a coil producing a magnetic field to move a ferrous core.
  7. Fitting a rare earth magnet under your bike would also be a fun way of collecting "souvenirs" on trips (or provide just enough attraction to make nails stand up just before your rear tyre goes over them) :LOL:.
  8. Old Hard Drives

    This is a bit of a late post to this thread but I just joined. I have always pulled my old hard drives apart for the bearings and magnets. I have been using the magnets as tool holders but recently had the bright idea of mounting one under my bike to see if it would trigger a set of lights that was giving me problems.

    I was almost surprised when it worked. So for anyone who is thinking about purchasing a GreenLight system and has an old hard drive you may already have just what you need.
  9. I usually push the starter button at lights where I am by myself and it seems to work. That said, if you do find some lights don't register you on a bike alone, call the telephone number displayed on the light switch/centre somewhere close by usually easily to see. There is a telephone number displayed and number to mention or else just remember the intersection(s) to write down when you get to a destination (that has pen + paper).
  10. i've taken to stopping right on top of the sensors and haven't had any problems at all for a while now. might look a bit odd stopping a few feet back but it works for me.
  11. i've also heard clicking the starter works... and it does seem to for me, can anyone confirm the physics of that?

    Also heard that coasting in neutral to the lights and putting your side stand down on the line of the loop also works...
  12. stop your bike on the + of the grid,give a lil rev always helps
    or and flash your high beam it triggers the sensor's
  13. We need a school physics teacher here :) But as I understand it, induction loop works by testing inductance of the loop of wire stretched under the road. Because at least some of your vehicle is made of metal when you stop above the wire it effectively changes the resistance of the core, thus changing inductance of the loop.

    So, starting the motor, revving it up, flicking the lights and other such things intended to create fluctuations of electromagnetic field should have no effect whatsoever, because this is not what inductance is about. Putting the stand down does have an effect, because it brings another lump of metal closer to the loop.
  14. This page gives a pretty good explanation on the technology behind the triggers at intersections.
  15. I know of several traffic light loops which are triggered by my mountainbike, and I expect that that could be part of the design criteria to "capture" bicycles too.

    There is very little steel in my mountainbike - the chain, the pedal shafts, the gear clusters, the axles and the bottom bracket bearing assembly.

    Apart from faulty loops could the problem be due to motorcyclists going past the loops to wait right on the edge of the intersection?

    There are also times when, due to traffic light controller computer malfunctions, a particular light sequence does not occur as scheduled. Not even a car will trigger it then. We had that happen several weeks ago.


    Trevor G
  16. If none of the above suggestions work, you could always get off the bike and jump up and down on the sensors.... :roll:
  17. You're welcome to try, but unless you're wearing metal boots I think you'll just give people a good laugh :p
  18. There's a traffic light from olympic park to parramatta rd that didn't seem to respond to anything, I had to get off the bike and press the pedestrian crossing button, worked like a charm, the damn traffic lights changed while I was walking back to the bike.
  19. There's a couple of sets of lights around Launceston that won't change for bikes. My mate and I got caught last week, late at night. There were a couple of cars around that but they were all going the other direction so their lights stayed green and ours were red. We lined our bikes up, shuffled them around, nothing.

    So after what seemed like ages and still no cars in sight behind me, I flicked her into neutral, got off, ran over and pressed the pedestrian button. My friend nearly pissed himself laughing but undoubtedly, the second I considered running the light would be the second a cop showed up. I wouldn't have done it if there hadn't been two of us though.
  20. yeah? then there must be somthing wrong with one of the sensors at my local area, i rode up to a main road, stopped at lights, and waited for two repeats of lights sequence...

    pissed off so I rode up to the foot path and pressed that button...