I haven't seen the output from those but I highly doubt you could tell is a car was stopped for three seconds with them. It's an inductive loop so it should push a signal when there is a vehicle moving above but most loops are big enough for more than one vehicle (to allow you to be in a range of positions and still trigger the light). In any case, I highly doubt there is a tie in to fixed infrastructure. It would be easier and smarter to use commonly available optical recognition/processing to decide when to flash.
Iirc, they have speed on the ticket (
@sburns can confirm). Not sure if that is radar or time between pics/distance calc.