You have to place your bike properly over the induction loop. Induction loops work by detecting a change of inductance and even aluminum or carbon fiber bikes can be used to trigger them.

One of my favorite riding moments of last year was rolling up on a stop where a large group of full-dress Harleys were impatiently waiting for the left turn light to change for them. Apparently the two riders in front were not willing to roll on the red, so they were holding everyone else up, and none of their bikes were properly positioned over the induction loop to trigger it.

As I approached on my mountain bike, I swung very close to the front end of the 2nd rider in line and nearly touched the 1st rider's rear fender, to put myself directly over the induction loop, and then I did a quick trackstand that triggered the light. Then I hopped a couple of times to swing my front end clear of the 1st rider's bike and then I rode to the front of the line, just as the light changed.

As they passed me in the turn every passenger and several riders stared me down as if I had just levitated a car. I just smiled and nodded.