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  1. #1
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    Stoplight Triggering

    At a stoplight that changes only when a vehicle triggers the magnetic sensor wire circles in the pavement, the large-diameter circles designed to detect cars typically don't read me standing astride my bike, so I never get a green light.

    If I lay my bike down flat, so the metallic frame covers a substantial portion of the circle only a few inches above the pavement, then the magnetic sensor usually does read it and I get my green light.

    I'm not "into" the road bike community enough to know: is this a well-known trick I've merely re-discovered? Or is this something I should spread around for others' convenience?

  2. #2
    IdontShootPeopleAnyMore
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    whats more dangerous laying down in the middle of the road or running a red light?
    What mountain bike forum do pirates use? .....



    MTB-arrrrrrrrrrrrrrr

  3. #3
    Ovaries on the Outside
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    Quote Originally Posted by DriveByBikeShooting
    whats more dangerous laying down in the middle of the road or running a red light?
    What the ****? Is laying your bike down at a red light dangerous at all? You do realize that one isn't lying down with the bike....

    To OP- laying down a bike on a magnetic strip is proper form. Sometimes they don't trigger, so burn the light. I try to avoid burning reds/stops because I think it is a bad example for cycling.

  4. #4
    Squeaky Wheel
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    If your wheel alone won't trigger the light, call your local road department and ask them to adjust the sensitivity. Around here, all the detector loops have a little white "X" painted where you should put your front wheel for reliable detection. I've see the local road department techs adjusting the loops...they use a bike wheel.

  5. #5
    weirdo
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    I don`t think sensitivity is normally as big a problem as being in the exact right place. I`m also guessing that laying the bike over sometimes works because in the process it ends up directly over the sensors at some point rather than because the frame is closer to the coils. Of course, I could be wrong about that . The nice white Xs sure would be sweet. Our intersections are usually so patched, repaved, and funky looking that there`s normally no way to tell just where the sensors are.

    All I can say for sure is that you`re battling a familiar issue wth the triggering signals thing. It`s an eternal problem for most of us, so you aren`t alone.

    And welcome, Vijeta.
    Recalculating....

  6. #6
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    Just ride up to the signal pole and push the pedestrian crossing button

    There are no "sensors" in the pavement, just wires run in conduit, usually in rectangular shape. When there is enough mass of metal over the wire it alters the electromagnetic field telling the signal controller that it's time to change the light. Standard loops for cars are fairly big and the rectangular shape would most likely completely encompass a person on a bike. If you can tell where the conduit/wire runs, usually by a patch or saw cuts in the pavement, you are better off trying to be on the outer edge and directly over one of the runs of conduit/wire than smack dab in the middle. They are starting to put in smaller loops and loops of different configurations that will detect a bike much easier, but obveously those won't be everywhere.

  7. #7
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    In Tempe they have started putting bicycle buttons next to the curb so you just stay in the street and can push the button. It's quite nice! If there isn't one I just ride up on the sidewalk and hit the pedestrian button. I only run a light if nobody is anywhere around to see and I have been waiting too long, don't want to give any more fuel to the angry motorists when they decide to complain about cyclists in their area.

  8. #8
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    Recently installed or newly paved intersections with obvious octagonal wire pickup loops at the two intersections I have trouble with.

    Both have triggerd once each when I approached the stop line since they were installed. I suspect the loops are on some timed, decreasing signal trigger, algorithm, so after 10 minutes without changing my bike is good enough. I have tried every spot on the two forward loops and there has been no joy in Mudville. I have a steel frame and a big ol' cup and cone BB to trigger with. One state (Utah?) allows you to proceed after stopping and waiting for a break in traffic and Indiana considered doing the same. No luck. They do allow treating it as a stop sign if it is malfunctioning. So If after the usual trigger time no cars have lined up behind or opposite ot trigger the light, I will treat it as malfunctioning, as it is from my perspective. May not stop a ticket, but maybe it will. They don't have pedestrian buttons, and one doesn't even have crosswalks! Very lame.

    The lay the bike down technique is intriguing. Next time I am the sole transportation device awaiting a light change I will try it. Nothing to lose if it doesn't do the trick. I'm standing around anyway,

  9. #9
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    Many of the traffic lights in my area wonít even detect my Harley so I end up making a couple different turns to approach from a different direction or using the pedestrian crossing devices to trigger the lights.

  10. #10
    ~Disc~Golf~
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    Quote Originally Posted by haager
    ...

    There are no "sensors" in the pavement, just wires run in conduit, usually in rectangular shape.
    Quote Originally Posted by haager
    When there is enough mass of metal over the wire it alters the electromagnetic field telling the signal controller that it's time to change the light. ...
    hmmm.
    Honestly... ahh I give up

  11. #11
    weirdo
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    Quote Originally Posted by highdelll
    hmmm.
    Yup, senseless.
    That`s okay, though.
    Recalculating....

  12. #12
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    Yes, wires CAN be sensors and the curent in them, the signal. The poster got his point across regardless of his definition of 'sensor'. Good enough.

  13. #13
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    Amen.

    What if you are a carbon fiber nut though- horseshoes on a string?




    .

  14. #14
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    Quote Originally Posted by grandsalmon
    Amen.

    What if you are a carbon fiber nut though- horseshoes on a string?




    .
    I've heard that a neodymium magnet epoxied to your sole will werk - never tried it though
    Honestly... ahh I give up

  15. #15
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    Quote Originally Posted by highdelll
    I've heard that a neodymium magnet epoxied to your sole will werk - never tried it though
    Don't get carried away with the Gauss, or you might stick to Manhole covers and grates!

    How ignominious (how often do you get to use THAT word?) would that be?

  16. #16
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    Quote Originally Posted by haager
    There are no "sensors" in the pavement, just wires run in conduit, usually in rectangular shape. When there is enough mass of metal over the wire it alters the electromagnetic field telling the signal controller that it's time to change the light.
    ...er well, there is a controller in the signal cabinet that senses the change in the electric field and tells the signal change the light.

  17. #17
    Ride Responsibly
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    Write your congress person and ask to allow bikes to treat stoplights and signs as yield signs, change the stupid laws.
    Until then wait thirty seconds then run the stupid light.

  18. #18
    Squeaky Wheel
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    Duplicate

  19. #19
    Squeaky Wheel
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    Quote Originally Posted by rodar y rodar
    I don`t think sensitivity is normally as big a problem as being in the exact right place.
    When properly adjusted, the exact right place does not seem to matter much. I can run over detector loops at 20MPH in a variety of spots and see the cross-street light change from green to yellow. The key is to ask your road department to adjust the sensitivity to detect bicycle wheels.

    Here are a couple of pages that talk about triggering lights in more detail:

    http://www.humantransport.org/bicycl...nals/green.htm
    http://www.humantransport.org/bicycl.../detection.htm

  20. #20
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    They often can't adjust the sensitivity with software or the electronic controllers, its the hardware of the loop itself. Not all systems are like this but ours are. Moving to camera sensors is the best way to go. That's what we're doing.

  21. #21
    weirdo
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    Here`s a good idea that`ll never happen. What if they put LED indicators under the green lamp that would show when the sensor (or not sensor) had been tripped? You pull up to the line and watch for the LED. If you don`t see it, move over or roll back a little or whatever until you know it`s registered your presense. Sounds cool to me for "perfect world" solution.
    Recalculating....

  22. #22
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    Quote Originally Posted by BrianMc
    Don't get carried away with the Gauss, or you might stick to Manhole covers and grates!

    How ignominious (how often do you get to use THAT word?) would that be?
    the magnet wouldn't be stationary
    Honestly... ahh I give up

  23. #23
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    I feel so left out - I don't believe we have any of those here in VT - or not on my commute anyways. When the light doesn't change it's just broken. In fact, one stayed red for a few days last year, until an accident occurred...then they fixed it.

  24. #24
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    Quote Originally Posted by highdelll
    the magnet wouldn't be stationary
    If you are rolling the light before it cycles, why carry the magnet? Some can post until the signal changes the light, those who can't could circle, but most will put a foot down and the picture of someone's foot held....

  25. #25
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    Quote Originally Posted by BrianMc
    If you are rolling the light before it cycles, why carry the magnet? Some can post until the signal changes the light, those who can't could circle, but most will put a foot down and the picture of someone's foot held....
    who said I was rolling it?
    Honestly... ahh I give up

  26. #26
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    Quote Originally Posted by rodar y rodar
    Here`s a good idea that`ll never happen. What if they put LED indicators under the green lamp that would show when the sensor (or not sensor) had been tripped? You pull up to the line and watch for the LED. If you don`t see it, move over or roll back a little or whatever until you know it`s registered your presense. Sounds cool to me for "perfect world" solution.
    This is actually a good idea. I'll have to figure out how to make that happen.

    The challenge would be to use a light that is visible, yet not blinding.

    So in our town, we can detect carbon fiber road bikes. But it is crucial to be placed on the most sensitve part of a 6' dia loop or a 6x6. The key is to get as much metalic parts near the wires imbedded in the pavement.

    On a 6x6, it is with your front hub on the top-left or top-right corner. On a 6' dia, it is about a third from the left or a third from the right. Basically your front hub and your back hub is over a sawcut. And to top it off for good measure, I turn my front wheel along the sawcut. Even carbon bikes have aluminum hubs, drivetrain, spokes and rim liners. This is enough to trigger the lights.

    (If you can't trigger in a Harley, chances are you are waiting in the center of the loop which is the least sensitive spot on the detector loop.)
    Just get out and ride!

  27. #27
    Frys With That, Please
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    Here in ID it's legal to proceed through a red light AFTER one stops and confirms that it is safe to do so.

    It's also legal to roll through a stop sign here too.

  28. #28
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    Quote Originally Posted by highdelll
    the magnet wouldn't be stationary
    Quote Originally Posted by highdelll
    who said I was rolling it?
    If the cyclist in question is not rolling, the magnet IS stationary. That is now OK?

    The "you" used in "If you are rolling a light" is a rhetorical device to help the reader enter the scene and understand why that magnet might not be moving. I was writing to anyone reading the reply.

    We are pushing towards OT here so I hope that explains things.

  29. #29
    weirdo
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    Quote Originally Posted by cda 455
    Here in ID it's legal to proceed through a red light AFTER one stops and confirms that it is safe to do so.

    It's also legal to roll through a stop sign here too.
    Yup, most of us are aware of that and, it`s part of the discussion in the current "Stopsign Question" thread. Although a lot of us ride that way, I for one (and probably a lot more too) am envious of you guys up there who get the law`s blessing to roll `em.
    Recalculating....

  30. #30
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    Quote Originally Posted by BrianMc
    If the cyclist in question is not rolling, the magnet IS stationary. That is now OK?

    The "you" used in "If you are rolling a light" is a rhetorical device to help the reader enter the scene and understand why that magnet might not be moving. I was writing to anyone reading the reply.

    We are pushing towards OT here so I hope that explains things.
    Jesus Christ on a cracker!! -
    One (1) - The action of pedaling (or back-pedaling) moves the magnet around.
    TWO (2) - a simple 'wag' of the shoe - let's say heel-down/toe-up.

    We are not pushing towards OT,
    YOU suggested that the cyclist is rolling.
    The Magnet idea certainly has validity, as if you understand Jr. High science class, a magnet passing over a wire will produce a current.

    I used to werk avionics on these things...
    <object width="640" height="505"><param name="movie" value="http://www.youtube.com/v/dNkP4WwJInE?fs=1&amp;hl=en_US"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/dNkP4WwJInE?fs=1&amp;hl=en_US" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="505"></embed></object>
    baddest plane that was, ever - F14D
    Honestly... ahh I give up

  31. #31
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    Quote Originally Posted by highdelll
    Jesus Christ on a cracker!! -
    One (1) - The action of pedaling (or back-pedaling) moves the magnet around.
    TWO (2) - a simple 'wag' of the shoe - let's say heel-down/toe-up.
    I was trying for a bit of levity, a bit of humor! I was NOT condemming the concept. In fact, I like it and plan to try it. (So we are OT!)

    I was having a hard time putting myself in your shoes to figure out where I messed up.

    I thought about the size I could fit on my shoe then I just took the idea to the silly extreme of someone putting on a magnet so strong they got stuck to things. Unrealistic, dumb, but funny IMHO. YMMV

  32. #32
    weirdo
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    If you mount the magnet on your own shoe, you won`t have to put yourself in Highdell`s.
    Recalculating....

  33. #33
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    I'm guessing the answer to my original question -- is this trick well-known in the road cycling world? -- must be "no", because no one has responded otherwise.

    Tried to keep the original post simple, didn't go into the technicalities of a conductive mass changing the inductance of the pavement pickup loop, thus changing the tuning of a resonant circuit creating a frequency change which the controller responds to. Ask your local ham radio operator about a grid-dip meter (or source-dip meter now that we're in the solid state age) if you want more info on how it works.

    Here in LA we do have small diameter sensor circles in some locations which are designed to pick up a person or a bike, and they work fine. It's the large ones designed for a car which don't always trigger for a cyclist.

    As for running the light, best is to set a good example as someone mentioned, but I might run the red in certain circumstances as a last resort (remote intersection, no traffic, etc.). However, the spot I'm thinking of is leaving the beach bike path at a parking lot exit to cross Pacific Coast Highway. With six lanes to cross, three each way, and the level of traffic during the day when I'm usually riding, given the average speed of that traffic, just running the red light would be SUICIDAL. Thanks anyway, but I'm riding to IMPROVE my health.

  34. #34
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    Quote Originally Posted by BrianMc
    I was trying for a bit of levity, a bit of humor! I was NOT condemming the concept. In fact, I like it and plan to try it. (So we are OT!)

    I was having a hard time putting myself in your shoes to figure out where I messed up.

    I thought about the size I could fit on my shoe then I just took the idea to the silly extreme of someone putting on a magnet so strong they got stuck to things. Unrealistic, dumb, but funny IMHO. YMMV
    Honestly... ahh I give up

  35. #35
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    Quote Originally Posted by Vijeta
    I'm guessing the answer to my original question -- is this trick well-known in the road cycling world? -- must be "no", because no one has responded otherwise...
    As for running the light, best is to set a good example ...., but I might run the red in certain circumstances ....However, the spot I'm thinking of ...With six lanes to cross, ... and the level of traffic ...when I'm usually riding, given ...that traffic, ... running the red light would be SUICIDAL. Thanks anyway, but I'm riding to IMPROVE my health.
    I would guess the lack of response is a 'no' too. It is a new one to me. I haven't tried it yet as I need a lull with no cars opposite or behind to trigger it so that I can. hasn't happened lately. One bike is 531 and the other 4020, so if it works I have near ideal candidates. I will post here when I get it done. I also plan the Magnet on the shoe trick.

    I agree about setting a good example at lights. There comes a point of waiting, where the light is malfunctioning with regard to me and my bike and in Indiana we can proceed after stopping for a red light that is malfunctioning.

    I also have one stoplight controlled intersection that is so busy as to be suicidal to run it but there is enough cross trafic to trigger it to date, so no issues have arisen there. I have a pair of stoplights on an alternate route. One I can go right instead of straight and eliminate the problem. The other is across a 6 lane which varies in traffic density a lot. When busy, so is my cross street so cars trigger it. If traffic is light, it is on both, and the stoplights on the main route make large holes. I'd be be nice to be able to trigger that one.

    Let you know.

  36. #36
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    camera sensor is not that much better, I have to put my bike sideways in the middle of the lane for it to turn green, missed it it stays red and it's a 2 minute wait.

    There are usually no cars behind me, I don't want to wait for one.
    When there is one occasional car, they see me putting the bike sideways and try to make myself appear bigger as if I saw a mountain lion, they honk at me.

    There is no predestrian crossing on that side and I would have to cross 3 times as a predestrian.
    Clipless pedals sucks for that though..

  37. #37
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    Quote Originally Posted by Vijeta
    I'm guessing the answer to my original question -- is this trick well-known in the road cycling world? -- must be "no", because no one has responded otherwise.
    I'd guess it's a "no." The better trick is to lay your bike diagonally.

    Remember, the loops are tuned to pick up passenger cars. Some semi-truck trailers are a bit tall and can get lost before picking up the rear axles.

    The inductance is along the loop wires. A bicycle, for all intents and purposes is a piece of paper standing on end (vertical.) This doesn't provide enough surface for the field to hit if you are parked in the middle of the circle or square. By leaning your bike diagonally, you create a bigger surface to cross the inductance field AND you put more of your bike where it is more sensitive.

    The most sensitive part of a 6' diameter loop is about 1/3 width into the circle. The most sensitive part of a 6'x6' square loop is along an edge.

    When the loops are buried before the top lift of asphalt and the sawcuts are not visible, I place my bike near where I think the loop is and lean my bike over diagonally. Otherwise I put my bike vertical in the area of most sensitivity.

    As to the question of video detection, it's a hit or miss. Unless the Traffic Engineer or Technician built a detection zone of bicyclist, there may not be a zone that a bicycle can trigger enough pixal changes to register a call. Again, calling the local agency that runs the signal can help to create bike zones.

    The latest technology (applied technology) is radar. It scans the intersection for anything moving and can detect pedestrians approaching the intersection and put in a call. Unfortunately, we haven't tried it out yet.
    Just get out and ride!

  38. #38
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    traffic002, any experience with a magnet triggering?
    Honestly... ahh I give up

  39. #39
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    Quote Originally Posted by traffic002
    I'd guess it's a "no." The better trick is to lay your bike diagonally.
    ... By leaning your bike diagonally, you create a bigger surface to cross the inductance field AND you put more of your bike where it is more sensitive.....The most sensitive part of a 6' diameter loop is about 1/3 width into the circle. The most sensitive part of a 6'x6' square loop is along an edge.
    Good stuff. Leaning it is definitely easier and less of a 'weird out' for a driver coming up behind.

    Interesting that the geometry of the loop affects the placement of the zone of greatest sensitivity. I don't have circles so any idea about octagonal loops and leaning? Are they squares with the corners cut off or distorted circles, or intermediate between the two (1/6 way inside, lean a little)? The two I can see yet are octagons. While the buried one I deal with, (if I remember correctly). is a square.

    Also curious about the magnet idea, if you have any info.

  40. #40
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    Quote Originally Posted by highdelll
    traffic002, any experience with a magnet triggering?
    I've heard rumors about this and discussions with folks wanting to make it work on motorcycles. But we've never tested it out. I suppose I could take my super strong magnet (about the size of a half dollar but can old 40#) and see if I can trigger our signal right outside City Hall. I would imagine it still depends on location of the magnet.

    The problem is they are trying to fix something that isn't broken.

    If I can trigger a signal with my carbon fiber bike, there is no reason you can't trigger it with your moped.

    So you create an electromagnetic field that, theoretically, disrupt the field produced by the induction loop. However, the electronics that read the deltas in inductance is tuned specifically for cars, trucks, motorcycles. Can the electronics work within the change that a magnet can make? IDK.

    I can, however, say that if I am more than 6" from optimum placement of my bike, then I do not get detected. There's a little more wiggle room with a steel bike and even more with a motorcycle. But if you just park in the middle of the lane, your probability of being detected goes way down.
    Just get out and ride!

  41. #41
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    The magnet alone makes no difference, it's the metal that makes the difference. The traffic controller sends and alternating current through the loop which generates an electric field. When metal comes into the field, eddy currents are induced in the metal and these eddy currents in effect work against the field lowering the overall inductance of the loop. This lowering of the inductance is what the traffic controller senses. So, you would be just as well off strapping a hunk of metal to the bottom of your shoe - the more conductive the metal the better (so a hunk of copper would probably work better than a magnet, but I have never tested it).

    On the cameras, I have found two things that work: first make sure you stop where cars normally stop to make sure that you are in the detection box, and then make yourself as big as you can (open your coat, raise your arms over your head, etc.). The other thing I will do when it is dark is to shine my headlight right at the camera.

  42. #42
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    Quote Originally Posted by woodway
    The magnet alone makes no difference, it's the metal that makes the difference. The traffic controller sends and alternating current through the loop which generates an electric field. When metal comes into the field, eddy currents are induced in the metal and these eddy currents in effect work against the field lowering the overall inductance of the loop. This lowering of the inductance is what the traffic controller senses. So, you would be just as well off strapping a hunk of metal to the bottom of your shoe - the more conductive the metal the better (so a hunk of copper would probably work better than a magnet, but I have never tested it).
    Electronic inductors have ferrite cores. One reason may be cost, but the most likely is ferrite is more highly inducible. (COuld Wiki, it but Ineed to go). I don't think copper is, or wouldn't inductors on copper layered PCBs raise havoc with the circuits thereon? A magnet presumed a DC current in the loop not AC, so it will only be as effective if it messes up the field, and a piece of mild steel may be more effective. Since I bave about 5.5-6.5 pounds of steel in frame fork and BB, and some of you with Carbon bikes have enough fasteners and pieces to get it done, so I guess I don't need an anvil on my shoe.

  43. #43
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    Well, like all things, it depends. Whenever you put inductors on a PCB you have to watch our for unintended side effects. A lot of engineering typically goes into making sure those circuits are operating properly.

    Back to the original topic - IMHO it all comes down to a properly tuned loop which will have not have any trouble detecting a bicycle wheel. No steel/copper/magnets needed.

    The city recently re-paved the road out in front of my office, and I can see the intersection from my ofice window. The day after the repaving, a traffic engineer came out to retune the loop detectors and put the little white "X"'s on the pavement that show where to put your bike wheel to trigger the light., He had a little rig with a bicycle wheel mounted in it that he placed over each loop, and then he went back to the controller and fiddle with the detection sensitivity. Pretty cool!

    If you are stopping on top of the loop in the right spot and it's not seeing you, call you local roads department and ask them to fix the problem!

  44. #44
    weirdo
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    Quote Originally Posted by woodway
    The day after the repaving, a traffic engineer came out to retune the loop detectors and put the little white "X"'s on the pavement that show where to put your bike wheel to trigger the light., He had a little rig with a bicycle wheel mounted in it that he placed over each loop, and then he went back to the controller and fiddle with the detection sensitivity. Pretty cool!
    VERY cool- send that dude my way!
    Recalculating....

  45. #45
    ~Disc~Golf~
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    Quote Originally Posted by woodway
    ...

    If you are stopping on top of the loop in the right spot and it's not seeing you, call you local roads department and ask them to fix the problem!
    WOW - wishful thinking to the utmost!!
    Honestly... ahh I give up

  46. #46
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    Quote Originally Posted by highdelll
    WOW - wishful thinking to the utmost!!
    Not crazy. Maybe a bit optimistic. Worth a shot, though.

    1. Don't know yet if they are bad. Got to see if I can trigger the things in the suggested zones. I don't think so, as I was trying different spots, so I should have hit on it, but two suspected triggers suggests I may have accidentlly hit a very narrow sweet spot.

    2. Maybe some of the cheaper ones aren't adjustable?

    3. If adjustable, I'll be lucky to see it changed in 12 months given the speed of response to two other comments, but I suppose it is fodder for the stop check, and proceed if traffic allows when the light does not trigger.

  47. #47
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    Here's a helpful vidoe.

    I do agree that not all agencies have finely tuned loops. It's sad. But I did encounter that on some group rides.

    Anyway, check this out and see if it helps: http://www.youtube.com/watch?v=Sj-mN..._order&list=UL
    Just get out and ride!

  48. #48
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    Well, the one light I thought I triggered before, I have now triggered twice more placing the bike in the third of where I think the circle is. It is an Indiana Department of Transportation intersection. Octagonal loops I am treating as circles.

    The one I have the option to go right, instead, gave me a faster change than the car behind would have triggered so the jury is out, but it looks promising. The third and most difficult, if there is no traffic, has had trafffic so no valid test. Be nice to be able to obey all traffic lights. That REALLY sets motorists off (though maybe 50% don't stop when going right on a red light).

  49. #49
    weirdo
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    Cool vid, traffic! It really says something about a city`s public works dept when they`re willing to go to the trouble of proucing something like that for the benefit of cyclists.
    Recalculating....

  50. #50
    Squeaky Wheel
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    Lucky for me I work in a City (Bellevue, WA) that actually cares about promoting safe cycling. Here is a blurb from the transportation page on the city website:

    To activate a traffic signal when on a bike
    You don't have to push a pedestrian button to get a traffic signal to change for you on your bike. Stop on the "X" mark or on the image of a bicycle painted onto the pavement to change the signal. If you encounter a signal that does not change for you, make an online transportation maintenance request or call the Signal Shop at 425-452-6950.

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