The operation of vehicles is prohibited if:

Explanation

In both cases — both unforeseen displacement in the steering components and the absence of a fire extinguisher in a lorry.

The list of prohibiting defects has two kinds: mechanical defects and the absence of mandatory equipment. This question deliberately takes one example from each category to see whether you know that both carry equal weight.

Unforeseen displacement in the steering components and joints, or threaded connections not being tightened, means the steering is no longer reliable steering. The steering system is a chain of rods and joints that must transmit the angular movement of the wheel to the road wheels without delay. Any play in this chain shows itself first as "slack" in the wheel and the need for constant corrections, and at worst leads to a joint separating and a total loss of control — usually over a bump or in a turn at speed, that is, precisely where the load on that joint is greatest.

The absence of a fire extinguisher in a lorry is likewise enough on its own for a prohibition. A lorry carries more fuel, more load and often higher brake and exhaust temperatures; fire spreads faster in it, and if the cargo is flammable, the first few minutes are decisive. An extinguisher in a lorry plays the same role as a first-aid kit does for the occupants: the tool for those few minutes before anyone else arrives.

Exam note: in this chapter, whenever both items really are on the list, the answer is "in both cases"; the single options are correct but incomplete, and incomplete means wrong.

• This item really is a defect, but it states half the answer; choosing it means you have treated the absence of a fire extinguisher in a lorry as permitted. • The absence of an extinguisher is prohibiting on its own too, but if you choose only this you have overlooked play and displacement in the steering system — a defect directly affecting control of the vehicle.

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