Following too closely is an offence and is the cause of most rear-end collisions. The K53 system uses a time-based gap rather than car lengths, because the distance you need grows with speed.
The 2-second rule. Choose a fixed object the vehicle ahead is about to pass (a pole, a shadow, a line). When its rear passes the object, count "one thousand and one, one thousand and two". If you reach the object before you finish counting, you are too close. At 120 km/h a 2-second gap is roughly 66 m.
Increase the distance (to 3 seconds or more) when:
- visibility is poor;
- the road is wet;
- you are travelling fast;
- you are carrying a heavy load or towing;
- you are on a loose surface such as gravel.
A larger gap is also the correct response to a tailgater behind you. Never brake sharply to warn the driver; instead open the gap in front so that you can slow down gradually, and let the vehicle pass when it is safe.
The following distance is part of keeping a clear space all round your vehicle, which is the heart of defensive driving: it buys you the time to see a hazard, decide and act.