The operation of vehicles is prohibited if:

Explanation

When there are visible tears on the seat belt provided for in the vehicle's structure.

A defective seat belt — visible tearing on the webbing, a broken buckle or a failed retractor mechanism — prohibits operation of the vehicle. Note that the criterion is being "provided for in the vehicle's structure": if the manufacturer designed a belt for that position, that belt must be sound.

The reason for this strictness is how the webbing behaves at the moment of impact. In a collision the belt must withstand a force several times body weight and spread it across the pelvis and ribcage. The webbing's woven fibres carry this force only while they are continuous; a small tear creates a stress concentration point, and the webbing parts exactly there and exactly at the moment you need it. A torn belt is worse than no belt, because it gives the occupant a false sense of safety and stops him taking other precautions.

The fog lamp option is a familiar trap in this chapter. Fog lamps are optional equipment; not having them creates no prohibition, and only if they are fitted must they work properly and be used in accordance with the rules. Keep the general rule: the absence of optional equipment is not an offence, but a fault in, or the absence of, equipment provided for in the structure is.

• Fog lamps are optional equipment and not having them brings no prohibition; only if fitted must they be sound and used correctly. • Since not having fog lamps is not an offence, "in both cases" is wrong and only the torn belt matters.

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