The operation of vehicles is prohibited if:

Explanation

In both cases — both the absence of head restraints provided for by the design and fitting new and retreaded tyres on the same axle.

A head restraint is not a comfort item; it is a safety component that works in a rear-end impact. At that moment the body accelerates forward with the seat while the head stays behind and is thrown backwards; without a head restraint the neck bends over the seat edge and cervical injury occurs — the very injury that turns a low-speed collision into a long disability. So if the vehicle's design includes head restraints, their absence prohibits operation.

The second item comes from the "same axle, same type" rule. A new tyre and a retreaded tyre have different carcass stiffness, tread depth and behaviour. When the two sit on the same axle, under hard braking or on a wet surface the grip forces on the two sides are unequal and the vehicle is dragged about its own axis; on the steering axle that means a swerve and on the rear axle a spin. A retreaded tyre also has a lower thermal threshold and gives way sooner than a new one.

Memorise this chapter's key rule: on a single axle everything must be identical — size, tread pattern, type (radial or bias), winter or ordinary, new or retreaded. Any inconsistency on one axle is a separate item on the list of defects.

• This item is correct but incomplete; by choosing it you have treated fitting new and retreaded tyres on the same axle as permitted. • This is genuinely a defect too, but on its own it is not the answer; the absence of head restraints provided for in the design is independently prohibiting.

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