They change the light quickly, there have been many accidents through their use on emergency vehicals because the light changes unexpectedly. Many lights are programed to go to all way red, which means you will be obvious if you run the light..so I'd not have plates on the car when I did this. It will not "clear" traffic and thus you may have to drive into opposing lanes of traffic in an intersection. If you get caught, you could get busted for interference with a traffic control device. Locally, there is a person in prison who interfered wiith a traffic control device (removed a warning sign), caused a fatality accident, and is now doing time in "the big house". Other drivers will be very P.O'd and will all want your plate number so be warned! Many crews do not use them as they confuse drivers (people stop and block the intersection all the time as the light suddenly changes).