My father was a road engineer for 20 years.. There are no weight scale triggers.
The two most common are magnetic & light senor.
The one motorcycles have an issue with is the magnetic. As stated above, there is just not enough steel in modern bikes for them to set off the trigger. You can contact your local road owner, of course you need to know which one (city/state, county) and they may adjusted it, if they want to.
There are also hot spots in the magnetic loop. Some areas will place a white X on that spot. But the hottest spot is generally where all the lines meet. Put your greatest mass of metal (ie the engine) over that spot. That will increase your chances of triggering.
There are generally 2 or 3 loops as you approach the stop line, I try to cross the hot spot on each one as I approach.