Tidsafstand

Tidsafstand, or time headway, is a measure of the temporal separation between two vehicles traveling in the same direction on a road. It is commonly expressed in seconds and describes how long it would take for the following vehicle to reach the position of the lead vehicle at the follower’s current speed. Equivalently, it can be seen as the spatial gap divided by the speed of the following vehicle.

Definition and measurement: Time headway is often defined as the time difference, recorded at a fixed point, between the moments each vehicle passes that point. In practice, s ≈ h × v, where s is the spatial gap, h is the headway in seconds, and v is the speed of the following vehicle. Time headway is a key element in traffic flow theory and safety analyses.

Importance and guidelines: A larger tidsafstand reduces the risk of rear-end collisions and provides more time to react to sudden events. A common rule for drivers is the two-second rule under normal conditions; in rain, snow, or high speeds, a longer headway of three to four seconds is often recommended.

Factors and measurement: Tidsafstand is influenced by speed, driver reaction time, braking performance, weather, road conditions, vehicle characteristics, and traffic density. Modern vehicles use sensors to monitor headway for safety systems, while traffic engineers measure headway using road sensors or video data.

Example: At 80 km/h (about 22.2 m/s), a two-second headway corresponds to roughly 44 meters of spacing; at 100 km/h (about 27.8 m/s), it is about 56 meters.