How do traffic signal lights operate when the power goes out?

Traffic signal lights are important to keep cars moving. But what do we do when power goes out? 114 of Plano's 240 signals have battery backup. If power goes out, the signal automatically switches to the battery backup. It can operate for approximately four hours on battery power.

If the power is out for a longer period of time, the signal will switch to a flashing red signal once the battery reaches 40%. Treat intersections with flashing red lights as a four-way stop.

All battery backups are checked three times a year for one hour to make sure the battery operates as expected.

Intersections without battery backup can be quickly hooked up to a generator to allow for continued operation.

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