The same devices are used here to control traffic signals and they
tear the daylights out of AM radio reception as you drive over them.  What
one hears is a carrier with lots of 60 HZ modulation on it that drifts across
the station you are listening to as the car drives over the coil.  Some
motor cycles and bicycles don't have enough metal to register and cyclists
have been seen jumping off their bikes and hitting the crosswalk buttons
when there isn't enough traffic around to cycle the lights.:-)

        I think the emergency vehicles here have IR-based strobes that
can control the lights when a police car or fire truck needs to get somewhere
fast.

        I don't know what hardware is actually used, but traffic signals
always seemed to me like a perfect use for PIC's.

Martin McCormick