Which of the values below should you take into account when establishing the distance between the vehicle in front?

In the photo, you are driving along a wide multi-lane street in a city; there are cars driving in front of you, and a blue car on the right is braking. When setting the following distance from the vehicle in front, you should take into account the speed of the vehicles - answer A. Neither the length (B) nor the width (C) of the vehicles affects the required distance.

The Road Traffic Act requires the driver to keep the distance needed to avoid a collision if the vehicle in front brakes or stops. This distance depends above all on speed: the faster you drive, the longer the distance you cover during your reaction time and the longer the braking distance - at 50 km/h you cover about 14 m in one second, at 100 km/h almost 28 m. A practical rule is a gap of at least two seconds, counted from the moment the car in front of you passes a post or a sign; on a slippery surface you double this time. The Act confirms this link directly: on a motorway and an expressway the distance in metres must be at least half the speed in km/h, so at 120 km/h - 60 m. On other roads you choose the distance yourself, but again according to speed.

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