[DVBC] Everything (and more) that you ever wanted to know about traffic light sensors

[Bob Curtiss]

Any metallic object of sufficient size will trigger these sensors.  
The key is not magnetism, but inductance. Carbon fiber won't do it,  
but aluminum will. It's necessary that the sensitivity of the sensor  
device is set low enough to detect a bicycle, but not so low that  
vehicles in adjacent lanes will trigger the sensor. It's a balancing  
act.

Try riding along the embedded wire. This will result in the maximum  
interaction between the metallic bicycle wheels and the sensor  
circuitry. Note that carbon fiber wheels won't work at all. A group  
of cyclists can "gang up" on the sensor by crowding together on top  
of the embedded sensor wires. It's important to put the wheels  
directly above the wires for maximum effect.

Unfortunately all of this probably still won't work unless the  
sensor's sensitivity is set with bicycles in mind.

Here's a very informative article on the subject, from a bicycle- 
friendly source:

http://www.humantransport.org/bicycledriving/library/signals/ 
detection.htm

~Bob


On May 7, 2006, at 7:22 AM, Douglas Bower wrote:

> For those interested in knowing weather a neodymium magnet attached  
> to the bottom of your $200.00 light weight bicycling shoe can  
> trigger a traffic light read on.
>
>
>
> Drew Knox was able to provide 2 very powerful neodymium magnets for  
> testing.  The intersection of Broad St and Garfield Rd in Lansdale  
> has a traffic light that is configured to provide north, south  
> bound traffic a green light until an east, west bound automobile  
> approaches.  There appears to be no other way of triggering the  
> light to change.  Some traffic lights are configured to change by  
> approaching cars or by a timer.  This intersections traffic light  
> appears to have no timer configured, as I have sat at that light  
> for a very long time without the light changing.
>
>
>
> The sensing device is imbedded into the pavement about 30 feet  
> before the light.  I taped the biggest magnet to a piece of string  
> and waved it over the sensing wire.  I waved it around the corners  
> of the wire and along the entire length of the wire.  I was at that  
> intersection for over 20 min. no automobiles approached from either  
> side of the intersection and the light never changed.  I tied a 12  
> inch adjustable wrench to the string and waved it over the wire  
> with the same results.  After returning to my car I drove over the  
> sensor wire and the light tripped almost instantly.  So my  
> recommendation to all DVBC members is do not waste time attaching a  
> magnet to your shoes….
>
>
>
> I am interested in knowing what the Pennsylvania law is regarding  
> traffic lights that will not change.  I was told by a respectable  
> DVBC member that there is some provision in the law that allows you  
> to proceed through a light if it is not functioning.  The problem  
> with these types of lights is they are not not functioning, they  
> work exactly as they were designed.
>
>
>
> Doug
>
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