Speed cameras flash two times, once before the vehicle enters the intersection, and once in the intersection after the light has turned red, according to the San Francisco Municipal Transportation Agency. This automated system varies from state to state, however.
The second photo determines whether or not a citation is warranted. The automated enforcement system is most commonly used for red light violations, reports the Insurance Agency for Highway Safety. Some states use this technology to identify drivers who avoid toll booths, do not yield to flashing school bus warnings or ignore railroad crossing signals. The District of Columbia tickets drivers who do not yield to pedestrians.