You are driving a lorry. Which of the following factors should you take into account to keep a safe distance from the vehicle in front?

The question is about the factors that a lorry driver must take into account to keep a safe distance from the vehicle in front. That factor is the speed of the vehicles - answer A.

The Road Traffic Act states that a driver must keep the distance needed to avoid a collision if the vehicle in front brakes or stops, and on a motorway and an expressway this distance must not be less than half the speed in metres - at 80 km/h at least 40 m. So the distance follows directly from the speed: the faster you drive, the longer the distance you cover during your reaction time and the longer you brake, and the braking distance grows with the square of the speed. The power of the engine (answer B) affects acceleration, not braking, and the width of the vehicles (answer C) matters when passing an oncoming vehicle, not when driving behind someone. A lorry has extra reasons to keep a longer distance: it weighs from over ten to several dozen tonnes, it takes longer to brake than a passenger car, and when fully loaded its brakes heat up faster. A practical rule is at least three seconds behind the vehicle in front, and more on a wet road surface.

Legal basis: Art. 19 para. 2 point 3 and para. 3a of the Road Traffic Act (Prawo o ruchu drogowym)