This traffic light is used to regulate the traffic of

Explanation

Trams and also other public-service vehicles travelling in a dedicated lane.

The light you see in the picture has four eyes arranged in the shape of the letter T, and their light is white-moonlight, not red, amber and green. Those two marks alone are enough to tell you it is not a general light: it is the special light for trams and public-service vehicles travelling in a dedicated lane.

Reading it is done by counting the lit eyes. Movement is permitted only when the lower eye is lit and at the same time one of the eyes of the upper row is lit as well; left means a left turn, the middle means straight ahead and the right means a right turn. In this picture the lower eye and the middle eye are lit, so only straight-ahead movement is free. If the lower eye is out, no direction is permitted.

The reason for a separate light is that a tram and a dedicated-lane bus behave differently: a tram does not leave the rails and its stopping distance is very long, and a dedicated lane usually crosses the turning paths of other cars. By giving this flow separate commands, the junction's timing can be arranged so that the rails and the dedicated lane are clear at the moment the cars turn. The exam trap is the option "only trams"; the scope of this light goes beyond trams.

• This light commands all public-service vehicles inside a dedicated lane, not only trams and trolleybuses; it has narrowed the scope without reason. • "Only trams" is the commonest misreading, because everyone associates the T shape with trams; but public-service vehicles travelling in a dedicated lane obey this same light.

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