Which of the following signs is set to indicate a road train?

Explanation

The right-hand marking; three orange lamps mounted in a horizontal row on the cab roof.

In the picture two goods vehicles are seen head-on. On the roof of the right-hand cab, three orange lamps sit side by side at equal spacing; that arrangement of three is the identification marking for a road train, that is, a vehicle towing a trailer or semi-trailer whose combined length is far greater than an ordinary lorry's. On the roof of the left-hand vehicle there is only a triangular orange symbol, which is a different marking and has nothing to do with a road train.

The safety reason for this marking is the question of overtaking. At night or in rain, the driver behind sees only the rear lights and underestimates the true size of the combination. Overtaking a road train requires two to three times more clear distance, and if the driver realises mid-manoeuvre that he has misjudged the vehicle's length, there is no way back. Three orange lamps give that warning from a distance: this is a long vehicle, you need more time and space to overtake.

The exam trap is the "both markings" option, because both symbols are orange and both are roof-mounted. The correct criterion is not colour; it is the number and arrangement: three lamps in a row.

• On the roof of the left-hand vehicle there is a triangular orange symbol, which is a different marking; the orange colour is shared, but the road train marking is always three lamps in a row. • Both markings are orange and roof-mounted, and that is what makes them look alike, but only the arrangement of three lamps in a row means a road train; accepting both means losing the identifying criterion.

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