Multiple realities
(covers information from several alternate timelines)
A traffic light was a sign within the traffic from which drivers could see if they can drive or have to stop. Normally it had the colors green, orange, and red.
In the alternate reality, when Spock was chasing Khan Noonien Singh through the traffic, they passed streets with a futuristic version of traffic lights. (Star Trek Into Darkness)
When Captain Picard was watching outside of Dixon Hill's office window in 2364, he saw automobiles and two traffic lights. (TNG: "The Big Goodbye")
A deleted scene from TOS: "The Enemy Within" has Leonard McCoy nearly bump into James T. Kirk's good side in the hallway, prompting him to comment that there ought to be a traffic signal in the corridor. (Star Trek: Lost Scenes)