Well, he could always rob a bank...
Well, what could be more stable is if you set up a laser on one side of the road - one of those small lasers would do, just has to be powerful enough...
on the other side you place a solar panel (one of those small ones, a few inches wide/long) inside of a case with an opening (so that the only light that can reach the panel is if the laser is aimed at it)... make sure both setups are stable and wont move when a car moves by (vibration is ok, as the solar panel should be large enough to catch the laser if it shifts a few millimeters)... and that's basically it... make two setups like that, then you basically have yourself a timegate system