The operation of vehicles is prohibited if:

Explanation

In both cases; whether the body door lock or the cab door lock has failed.

Any lock provided for in the vehicle's structure must work — regardless of whether it is on a body door or a cab door. The failure of either prohibits operation of the vehicle on its own, and the two almost identical options in this question exist purely to see whether you go looking for an artificial distinction.

The safety reason is behaviour in a collision. A sound, latched door counts as part of the vehicle's safety structure and, in a side impact, distributes the force through the body. A defective lock means the door may open during the impact, and that is where the greatest danger arises: the occupant being ejected, one of the deadliest crash scenarios. Even in normal driving, an unlatched door may swing open in a sharp bend or a sudden manoeuvre and endanger not only the occupant but an overtaking vehicle or a motorcyclist alongside.

In this family of questions, wherever two options repeat a single defect with only its location changed — such as a body door and a cab door — the answer is usually "in both cases", unless the law has expressly made an exception for one of them; which it has not here.

• A defective body door lock really does prevent operation, but the law has not confined this defect to one door, and choosing it alone makes the answer incomplete. • A defective cab door lock is an offence too, but for the same reason it cannot be treated as the only instance of the prohibition.

Sources and content coverage · Report a content error