The operation of vehicles is prohibited if:

Explanation

Both a bus tyre tread of 1.8 mm and damage to the sealing of the hydraulic brake system.

Both items are on the list of prohibiting defects, and the key point of the question is the figure in the first option.

The minimum residual tread depth for a bus is 2 mm — higher than the 1.6 mm limit for a passenger car. So a tread of 1.8 mm on a bus is below the legal limit and not permitted, even though at first glance it looks like a "sufficient" figure. The reason for the stricter standard for buses is their mass and load: a heavier vehicle has a longer stopping distance and aquaplanes sooner on a wet surface, while the consequence of any error is multiplied across dozens of passengers.

Damage to the sealing of the hydraulic circuit is independently prohibiting too. A leak or ingress of air fails to transmit the pressure of your foot to the wheels; the pedal softens, its travel lengthens, and in an emergency stop there may be no braking at all. This defect is dangerous because it stays almost hidden in gentle driving and shows itself only at the critical moment.

Worth memorising: pair the three tread figures with the vehicle type — motorcycle 0.8 · passenger car 1.6 · bus 2 mm. The exam usually gives a figure that is permitted for one class and not for another; find the vehicle type in the question first, then measure the figure.

• Correct but incomplete; 1.8 mm really is below the bus limit of 2 mm and creates a prohibition, but this option ignores the brake defect. • Damage to the sealing of the hydraulic brake circuit is independently a ground for prohibition too; choosing it alone leaves the answer incomplete.

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