Two-second rule
A way of checking your following gap without measuring anything: two seconds in good conditions, double it in the wet, far more on ice.
Pick something fixed at the side of the road — a sign, a bridge, a marker post. When the vehicle in front passes it, start counting. If you reach it before you finish saying a two-second phrase, you are too close and need to drop back.
The reason it is expressed in seconds rather than metres is that it scales itself. A gap measured in car lengths means something different at 20 mph and at 70; a gap measured in time is the same amount of reaction room at any speed, which is exactly what you need it to be.
Two seconds is the dry-road minimum, not a target. Double it when the road is wet. In ice you may need ten times the distance. And the gap in front of you is also the gap someone else will use to pull into, which is a reason to restore it rather than to close it up.
11 practice questions on this
Each one shows the answer, and our note on why every other option is not it.
Car
Motorcycle
Lorry & Bus (LGV/PCV)
- You're driving on a motorway and it's raining heavily. What should you do when spray is causing poor visibility? The road
- You're driving on a motorway. What should you do if your view ahead is restricted by heavy spray? The road
- You're following a large vehicle. How can you improve your view ahead? The road
- When should you use the two-second rule? The road
Driving Instructor (ADI Part 1)
- When should your pupil use the 'two-second rule'? Band 1 road procedure
- Your pupil is driving on a fast, open road in good conditions. What advice can you give them to help them judge a safe distance from the vehicle in front? Band 1 road procedure
- You're driving on a motorway that has chevrons painted on the carriageway. In good weather, at least how many chevrons should be visible between you and the next vehicle in your lane? Band 2 traffic signs and signals, car control, pedestrians, mechanical knowledge