This traffic light prohibits traffic:

Explanation

Only the left turn is prohibited.

The four-eye T-shaped traffic light with white moonlight signals is the special light for trams and public-service vehicles, and the logic of reading it differs from an ordinary three-colour light. 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: upper left means a left turn, the middle means straight ahead, the right means a right turn.

In the picture the lower eye is lit and, from the upper row, the middle eye and the right eye are lit, but the left-hand eye is out. So going straight and turning right are free, and the only direction that is prohibited is the left. If the lower eye were out, movement would be prohibited in all directions — memorise this point separately, because the greatest number of mistakes occurs precisely here.

The safety reason for a separate light for trams is that a tram does not leave the rails, its stopping distance is very long, and its path often crosses the turning paths of cars. By giving the tram separate commands, the moment when the rails are clear can be allocated to the cars' turns and the side impact eliminated. The exam trap is that the mind looks for red and green; here there is no colour at all and you must simply count which eye is lit.

• The middle eye of the upper row is lit, so straight-ahead movement is permitted and cannot be listed among the prohibited directions. • Both straight and right are lit; this option has listed exactly the permitted directions in place of the prohibited ones. • The upper right eye is lit and the right turn is free; the prohibition concerns the left.

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