Tripping the Light Fantastic

Actually this is about tripping ordinary lights.

Those of us with non-ferrous bikes ie carbon, aluminum, or titanium know how frustrating it is to sit at a stop light that doesn't know we are there. It lowers our average speed and raises our ire. It's especially frustrating on timed rides, or when the weather is bad.

I saw a program on Netflix that claimed that a rare earth magnet could trip stop lights by interacting with the magnetic fields produced by the sensors. I bought some on Amazon paying $20 for a set of four. They weigh one ounce each. Never allow them to come into contact with each other. They are almost impossible to separate.

I took one and attached it to the inside of my left crank arm on the opposite side from the pedal. The crank arm is aluminum but the bolt that attaches the pedal is ferrous. I put some gorilla tape over it too so it wouldn't shake off. Don't put the magnet on the right crank arm because it will grab the chain every pedal stroke.

I rode my Lucky Greek 100k permanent on Friday night and I found myself alone at a red stop light five times. I put myself over a sensor and stood with my left crank arm down. I never had to wait more than 45 seconds for the light to change.

This isn't exactly a scientific test and I realize it might have just been coincidence that the light changed for me, but I'm pretty sure the magnet is working.

Update: I did some research and the magnet doesn't have any effect. It turns out that the sensors work by running alternating current through the sensor loops and detecting the change in impedance when a large amount of ferrous material is near the loop.

For those who are interested, the changing magnetic field in the loop induces eddy currents in your car that impede the creation and collapse of the magnetic field which occurs 60 times a second and incidentally warms up your car slightly. This effectively increases the resistance of the sensor and reduces the current flowing through it. It is this current reduction that tells the sensor that there is a car parked over the sensor.

Placing a magnet over the sensor changes the magnetic field, either increasing or decreasing it but as the sensor is looking at how the magnetic field changes over a timespan of a few milliseconds, the magnet is not detected. Even the effect caused by moving the magnet over the sensor is too slow to be detected.

So the effect was purely placebo. Bummer.