What does a traffic light signal indicate?

Explanation

You must wait for the permitting signal.

In the picture the light on the right of the junction has lit the red eye and the amber eye at the same time. This combination is an independent and fully defined signal: movement is still prohibited, and the only thing this signal does is give notice that the permitting signal is near. So your duty is to remain behind the stop line and wait for green.

Its rationale is practical: a driver who is warned a few seconds before green has time to engage the gear, release the handbrake and be ready to move. The result is an orderly start of the queue, prevention of a car stalling in the middle of the junction, and less stress at the moment of green. But this preparation must not turn into moving early; at that same moment a car from the crossing direction may still be clearing the junction, or a pedestrian taking his last steps.

The exam trap is to read red-and-amber as a "ready to move" light and equate it with permission to pass. The mark of a faulty light is something else — complete darkness or flashing amber — and it is in that state that you must act on the signs and the priority rules. As long as two steady eyes are lit, the light is working and is giving an order to stop.

• A faulty light is not announced by two steadily lit eyes; a fault usually appears as complete darkness or flashing amber. • Obeying the signs is relevant when the light is off or on flashing amber; here the light is active and issuing its own command.

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