I always seem to get stuck behind people - usually tourists (or tourons as we sometimes call 'em) who are waiting for the stop sign to turn green!
You reminded me of one of my favorite jokes:
Q: What's the difference between a drunk driver and a stoned driver?
A: The drunk driver will run the stop sign. The stoned driver will stop, and wait for it to turn green.
okay, okay, stop throwing rocks at me.
The magnet is a good idea. The same effect could be had with a 8" long piece of 1" keystock on a lanyard. A 1" by 1" by 8" piece of mild steel has other uses that are too... complicated to go into here.
seriously, any chunk of ferrous metal can set the light off, magnet or not. The big loop set into the pavement has an AC current going through it, which makes it resonate at a certain frequency. (like a radio antenna) When a big piece of metal gets near it, the frequency changes, the controller picks it up, and the light changes. Needs to be something solid though. The thin steel in some rims and in the spokes isn't enough.
Maybe the best way to think of it - it's a big metal detector.
Induction is one of the coolest electrical effects, IMO.
-Mark