Traffic signals do a very good job of directing motorists, cyclists and pedestrians through intersections, typically automatic 24/7/365. This is done without requiring much more than some periodic maintenance and electricity but when the power is interrupted, these reliable traffic sentries become extremely dangerous and inefficient.
Although drivers are required to treat a controlled intersection with an inoperative signal as an all-way stop, installing a battery back-up system for each signal is the ultimate safeguard against power outages while drastically improving safety.
A typically battery back-up system can provide power for full operation of a traffic signal for at least four hours and are automatically kept charged when not in use.