" I thought that intersection detectors worked via inductance, not on the actual weight or size of the vehicle

Those loops generate a small electrical field that is disturbed by large metal/metal-containing objects (like cars, which also generate their own electrical field), and this disturbance is what causes the light to trigger. Size may only be a problem if you're not sitting fully on the inductors.

Though I don't ride a motorcycle to confirm this, I've heard that if your bike won't trip the light: First, make sure you're sitting on the coil - look for a rectangular patched piece of asphalt - and then, with due caution, turn the bike off and back on again. The starter coil should generate a strong enough electical field for the sensor to notice and you'll soon be on your way. "

" Encourage your road department to install cameras at the intersection. They can even pick up bicyclists. They even work when someone doesn't stop in the correct place. The only problem is when they get out of alignment, such as a huge wind event, knocking them into the wrong direction. "

" That's a good idea, far better than "go find another road to ride your motorcycle on" - provided of course that they're -only- sensor cameras, and not used for surveillance. "