At what traffic light signal is the car driver allowed to complete a U- turn?

Explanation

Only on a green signal.

The general rule says that a driver who has entered a junction on a permitting signal must complete his manoeuvre in the chosen direction, regardless of the signal of the exit light. But that rule has an important exception: if, within the route and before the next light, there is a stop line or a "STOP" sign, the driver is obliged to obey the signal of each light separately.

In the picture that is exactly the situation. The red car is making a U-turn, and on the central strip a light is fitted whose red eye is lit, with the "STOP" board — the stopping point — directly beneath it. So this light defines an independent halt for you: you must stop before the stop line and complete the U-turn only when that same light turns green.

The safety reason is simple: a road with a central strip is in practice two independent carriageways. The green signal that let you through the first half says nothing about the traffic in the second half; if you carry on without regard to the second light, you turn straight in front of a flow that has its own green, and a side impact at full speed follows. The exam trap is the very rule "complete your manoeuvre"; the presence of an intermediate stop line sets that rule aside.

• The red light inside the junction, together with the stop board beneath it, gives an order to halt; continuing the U-turn on red means entering a through flow that has a green. • "Any signal" is tempting on the basis of the completing-the-manoeuvre rule, but the presence of a stop line before the second light invalidates that rule and makes obeying each light separately compulsory.

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