«While driving, vehicles must maintain a safe distance from the vehicle ahead such that timely stopping is guaranteed in all cases and collisions with vehicles ahead are avoided.» Thus states Article 149 of the Highway Code. There is no standard distance; the factors defining it are many and varied: road conditions, weather, vehicle condition and – above all – the driver's condition.
How much space is needed for a "timely stop"? This space is the safety distance. It is calculated by summing: the distance covered by the vehicle during the perception, reaction, and mechanical braking activation time + the mechanical braking distance. Let's try to "translate" this formula into meters.
Reaction time is the time between when we perceive a danger and the start of braking. Under optimal psycho-physical conditions, it is about 1.5 seconds; during this time, the car continues its journey unimpeded. Let's do some calculations. If we are traveling at 50 km/h, the car will cover 20 meters; at 100 km/h, it becomes 40 meters; at 130 km/h, the distance extends to 55 meters.
ABS and braking systems help reduce braking distance, but they cannot eliminate it! From the moment the brakes engage, quite a bit of road is still covered before stopping. Under optimal conditions, at 50 km/h, the braking distance is 10 meters; at 100 km/h, it takes 40 meters; if we travel at 130 km/h, we will stop after covering 80 meters. Note: when speed doubles, braking distance quadruples!
These reference indications for safety distance apply under optimal conditions, but they can increase if the person at the wheel is tired, or if the asphalt is wet or icy.
Some cars already have an adaptive cruise control system that maintains a constant safety distance between vehicles. But if you don't have one, the three-second rule allows for a good approximation of maintaining the correct distance. Look at the car in front of you and when it passes a road sign or under an overpass, for example, count to 3. If you reach the same sign or under the same bridge before the 3 seconds are up, you are too close. Always be cautious!
