You drive at 55 mph on a dry highway in good weather. The car ahead passes a road sign, and you count: your car reaches the same sign 3 seconds later. Under the handbook's following-distance rule for your speed, what is true about your gap?

Correct answer: It is too short, because above 30 mph you need at least 4 seconds in good conditions.

Why

At 55 mph your car travels about 80 feet each second, so each second of gap gives you a lot of room. The average driver needs about 1.5 seconds to see a danger and start to brake, and the car then needs more distance to stop. Count the seconds after the car ahead passes a fixed object, and add time when the road is wet, crowded or hard to see.

Verified against Texas Driver Handbook · Following Distance · p. 51