Driving Safely: Space, Speed, and Control
Space and speed
Almost every Driving Safely question reduces to one idea: a heavy vehicle needs far more room to stop than a car, and the room required grows with speed. Scan 12–15 seconds ahead, and remember that 15 seconds is a much longer stretch of road at 55 mph than at 25 mph.
Following distance
Do not memorize car lengths. Use the time-and-length rule: below 40 mph, allow at least one second for every 10 feet of your vehicle's length; at 40 mph and above, add one additional second. Add more space in rain, at night, in fog, and when following a motorcycle or any vehicle that blocks your view of the road ahead. If you cannot see the road past the vehicle in front, you are too close.
Controlling speed
Brake early and smoothly. Controlled braking means hard braking in a straight line without steering; stab braking is the alternate technique for vehicles without ABS. Before a downgrade, select a gear low enough to hold the speed with engine braking - roughly the gear you would need to climb that grade - because relying on the service brakes overheats the drums and causes brake fade.
Traps
Questions swap 'one second per 10 feet' for 'one second per 20 feet', or flip whether the extra second applies above or below 40 mph. Others suggest swerving instead of braking, or pumping air brakes to build pressure back up. A lightly loaded truck does not stop in a shorter distance than a loaded one; the brakes are the same.
Rule of thumb
A 60-foot combination traveling 45 mph needs 6 seconds for its length plus 1 second because it is over 40 mph - about a 7-second gap.