Tuesday, December 18, 2007

[Cyclelicious] New comment on Traffic lights and bicycles: The technical explana....

Bob Shanteau has left a new comment on your post "Traffic lights and bicycles: The technical explana...":

Brian suggested using a magnet to trip actuated traffic signals.

Sorry, but a loop detects conducting metal. They work like the metal detectors people use to find coins at the beach. Of course, a loop at a traffic actuated signal needs a larger piece of metal than a coin, but not more massive, such as the bottom of a car.

A piece of conducting metal causes an decrease in the inductance of the loop and therefore an increase in the resonant frequency of the oscillator circuit in the detector. Sorry, but there is no way that a permanent magnet can cause a change in the inductance of a loop in an oscillator circuit. Just ask any electrical engineer or physicist.

So you want to try a magnet anyway but can't tell when you have been detected by a loop at a signal? Buy a metal detector at your local outdoor store and see if it detects your magnet. I would be curious to learn what you find out.

If you really want to increase your chance of being detected at a traffic signal, then wrap several turns (the more turns the better) of insulated magnet wire (try Radio Shack) around your front wheel and splice the ends together, insulating the splice. You can use thin magnet wire (size does not matter) under the rim tape of a clincher rim with electrical tape around the splice. Then stop with your front wheel directly over the slot of a loop, if you can see it. If you cannot see the loop, then stop about 3 feet from the edge of a 12 foot travel lane. Or you can try asking your local friendly traffic engineer to paint a bicycle detector symbol over the loop slot.

If you cannot see the loop slots, do NOT stop in the middle of the lane!!! That is where most loops are LEAST sensitive to vertical pieces of metal such as a bicycle wheel. (There is an exception with figure-8 shape loops, but if you can't see the loop, how do you know what shape it is?)

Posted by Bob Shanteau to Cyclelicious at 12/18/2007 01:54:00 AM