Two-second rule

The two-second rule tells a defensive driver the minimum distance needed to reduce the risk of collision under ideal driving conditions.

At a normal speaking rate, this sentence takes approximately two seconds to say and serves as a reminder to the driver of the importance of the rule itself.

The TailGuardian distance advisory decals recently adopted by Stagecoach Buses in the UK use the two-second rule in their calibration.

[3] Advisory Decals for 30, 50 and 70 mph are calibrated to be invisible outside those safe distance, only rendering themselves visible once the car following has entered the safety zone for the speed that they are travelling.

Factors that make driving more difficult include poor lighting conditions (dawn and dusk are the most common); inclement weather (ice, rain, snow, fog, etc.

For example, a fatigued driver piloting a car in rainy weather at dusk would do well to observe a six-second following distance, rather than the basic three-second gap.

The three second rule is a time for the defensive driver to judge the minimum safe trailing distance to help avoid collisions under ideal driving conditions. The red car's driver picks a tree to judge a two-second safety buffer.