After the permitting traffic light signal comes on, we can enter the intersection

Explanation

Only when you intend to turn or make a U-turn.

In the picture the traffic light on the right is green, but on the far side of the junction a queue has formed: a white van and several cars with their brake lights on have filled the carriageway, and there is no free space for your car on the other side of the junction. That very scene is the core of the question.

A green signal only permits movement; it does not give an unconditional right to enter the junction. You have no right to enter the junction if the congestion ahead of you would force you to stop inside the junction and obstruct the movement of vehicles on the crossing route. See the safety and functional reason in that same picture: a car stuck in the middle of a junction locks the whole junction the moment the crossing route's light turns green. As several cars repeat this, the junction reaches a knot that no light can undo, and the path of emergency vehicles stays blocked too.

The exception comes out of that same logic: if you intend to turn right, turn left or make a U-turn, your exit path is not the blocked road ahead; you leave the junction towards a side that is free and therefore do not remain inside the junction.

The exam trap is the common notion "green means go". Before entering any junction, look at the free space on the far side, not just at the colour of the light.

• "In all cases" is the instinctive reading of a green light; but green is permission to move, not the lifting of the prohibition on entering a junction whose far side is congested. Straight-ahead movement in the situation shown would leave you stopped in the middle of the junction and block the crossing route.

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