On a 30 mph street, you keep a 4-second gap behind the car ahead. Now you follow a car on the freeway at 65 mph. How should your following gap change?

Correct answer: Keep at least 4 seconds, because a time gap grows in feet as your speed goes up.

Why

The faster you go, the more distance you need to turn, slow down or stop. A time gap grows with your speed: when the car ahead passes a fixed object, such as a sign, count the seconds until you reach it. If you get there before you count to four, drop back. Add at least one more second for each bad condition, such as rain, snow, ice or heavy traffic.

Verified against Wisconsin Motorists' Handbook · High-speed following · p. 14, 15