Originally Posted by cyccommute

Unless the road has been repaved since installation of the loop, the location of the wires is pretty clear. The wires are installed in the ground after the pavement has been cut and the cuts filled with tar. Most of the figure 8 ones look like this



Position your bike right over the middle of the loop. If the loop has been recovered due to an overlay job, then finding the coil is nearly impossible. Those are the ones I usually can't trip.

Once you learn the trick to tripping the light, you can amaze your friends on those high speed highway crossings!