Traffic light

Traffic lights were signalling devices positioned on roads to control competing flows of traffic. Cars were meant to stop at red lights to allow others to cross, (TV: Kiss Kiss, Bang Bang) while green lights allowed vehicles to proceed without stopping. (PROSE: Slow Decay)

The Torchwood SUV could change traffic lights so that they were green before the vehicle reached them, allowing Torchwood Three to get to their destination sooner. (PROSE: Slow Decay)

A Universal Remote Control could turn early 21st century traffic lights red. (AUDIO: Asylum)

In River Song's World, where all of Earth's history occurred at once, a Roman soldier on a horse waited for traffic lights to turn green as cars went by. (TV: The Wedding of River Song)

On arriving in Pete's World, Mickey Smith, who was acquainted with the idea of parallel universes that diverge from the normal world, suggested blue traffic lights as a difference. (TV: Rise of the Cybermen)