While driving behind another vehicle, under good conditions, you should allow at least one second between your vehicle and the vehicle ahead for each ____ feet of your vehicle length.

Follow far enough behind other vehicles (at least 1 second for each 10 feet of your vehicle length, plus another second if going over 40 mph). Look far enough down the road to avoid being surprised and having to make a sudden lane change. At night, drive slowly enough to see obstacles with your headlights before it is too late to change lanes or stop gently. Slow down to a safe speed before going into a turn.
[CDL DRIVER MANUAL FINAL]