What color traffic light means 'go'?

The traffic-light color that means “go” is green.

Modern traffic signals generally use red to mean stop, yellow or amber to warn that the signal is changing, and green to permit traffic to proceed. A green light does not always mean drivers may move without caution: turning vehicles may still need to yield to pedestrians or cross traffic, and intersections must not be blocked.

The first known mechanical traffic signal was installed near London’s Parliament Square in December 1868. Electric three-color signals developed later, and the familiar red-yellow-green arrangement spread internationally. The colors also connect with older railway signaling practices, where red indicated danger and green eventually came to indicate a clear route.

A common mix-up is assuming green means unlimited priority. In the United States, a steady circular green permits movement in permitted directions, subject to yielding rules. Green arrows are more specific: they authorize movement in the arrow’s direction, while still requiring attention to pedestrians and other road users. Japan is another interesting case: its go signal is green, although it is traditionally called “blue” in Japanese.