When making a left turn

Explanation

After entering the junction, stop before the second "stop line" and wait for the green light.

In the picture the carriageway is divided into two parts by a green central island, and each part has its own stop line and its own independent light. The light of the first half has permitted you to enter, but that permission is valid only as far as the second stop line; passage through the second half depends on the separate signal of that half. So the left-turn manoeuvre is performed in two stages: entry and a stop before the second stop line, then passage on a permitting signal.

The safety reason for this division is clear: at wide junctions, the flows of the two halves are run on different phases. If a driver went forward to the middle of the junction on the first half's green and carried on regardless, he would enter the second half at precisely the moment the perpendicular flow has received green. Stopping in the space between the two stop lines keeps the car in the safe area provided for it and also prevents the junction from locking up.

Worth memorising: every "stop line" is an independent obligation. If you see two stop lines at a junction, know that you are facing two lights and must read each of them separately. The exam trap is to take the first light's green as permission to cross the whole junction.

• Performing the manoeuvre without stopping means ignoring the second stop line and the independent signal of the junction's second half; that is exactly where the car enters a perpendicular flow already in motion.

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