A tractor-trailer is traveling at 45 mph. Using the AAMVA following-distance guidance for combination vehicles, what should the driver add beyond the base rule of 1 second for each 10 feet of vehicle length?

AAMVA CDL Manual, Section 6.1.2 'Steer Gently,' p. 6-1

Following distance is the main defense against having to make a sudden lane change, which is exactly the maneuver that triggers rearward amplification and crack-the-whip rollovers. Applying the extra second above 40 mph gives a combination driver more room to react smoothly instead of suddenly.