The operation of vehicles is prohibited if:

Explanation

If the seal of the hydraulic brake transmission has been broken.

A hydraulic brake system works on a simple principle: fluid is incompressible, so the force of your foot reaches the wheels undiminished — provided the circuit is completely sealed. The smallest leak breaks this chain; first the pedal goes soft and long, then you have to pump it twice, and finally it goes to the floor without the car slowing at all. That is why the law sets no tolerance for this defect: any loss of sealing, to any degree, prohibits operation.

The main danger is its suddenness. A leak usually does not show itself in gentle everyday braking and turns into a total loss of braking precisely in an emergency stop — that is, when circuit pressure reaches its maximum.

As for the tyre option: a residual tread depth of 1.8 mm is still permitted for a passenger car, because the legal minimum is 1.6 mm. The figure was chosen to sit close to the limit and create doubt, but it is still above it and constitutes no offence. Memorise these four figures: passenger car 1.6 mm, lorry 1 mm, bus 2 mm and motorcycle 0.8 mm. Anything equal to or above these limits is permitted; only below them is it an offence.

The general rule of this chapter is the same: the "in both cases" option is correct only when both items really are on the list of prohibiting defects; one sound item invalidates the whole comprehensive option.

• 1.8 mm is above the permitted limit of 1.6 mm, so it is not yet an offence — although the tyre is nearing the end of its life and would be better replaced. • "In both cases" requires both items to be defects; since the first item is still permitted, this option is ruled out automatically.

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