The next time you’re sitting at a red light that looks as though
it will never go green, refer back to this: On-demand signals
use what they call “induction loop vehicle detectors” to sense
when a vehicle is waiting at a light. These detectors are
essentially metal detectors embedded into the pavement. They
work by sensing changes in an electromagnetic field and have
nothing to do with the weight of the vehicle. You can often see
evidence of loop detectors as lines cut into the road surface
just behind the crosswalk. Wire sensors are embedded in these
cut lines, and it’s possible to trigger a light by placing your
bicycle wheels directly on top of one of the wires to disrupt
the magnetic field. Some sensors seem to be more sensitive than
others; in those cases where the light isn’t initially
triggered, I’ve had some success by leaning my bike over toward
the inside of the detector loop. In cases where there are two
side-by-side loops, lining up over the center where the two
loops meet doubles your chances of