Driving Combination Vehicles Safely
Driving Combination Vehicles Safely tests the speed, space, and steering habits that keep a heavy articulated rig stable. The exam expects you to translate vehicle length into following distance and to recognize how trailer weight changes braking and cornering.
Core rules
Use at least one second of following distance for each 10 feet of vehicle length, plus one second for speeds above 40 mph. A 60-foot combination at 55 mph needs about 7 seconds. Look 12 to 15 seconds ahead. Steer smoothly and brake before curves, not in them. Check mirrors often and remember that the trailer cuts inside the tractor's path, which is offtracking. Doubles and triples exhibit rearward amplification, so a small steer at the tractor can swing the rear trailer much farther.
Worked example
A 65-foot doubles rig follows a car at 250 feet at 55 mph. At 55 mph, 250 feet is about 3 seconds. The minimum is 6.5 seconds for length plus one second for speed, or about 7.5 seconds. The driver is more than four seconds short and should open the gap.
Downhill and traffic control
Select a safe gear before a downgrade and use engine braking or a retarder to avoid overheating the service brakes. Increase space when traffic is dense, because a combination needs longer to stop and cannot change lanes as quickly. Check height, weight, and bridge limits before choosing a route.
Traps
Using passenger-car following distance; braking hard in a curve; assuming the trailer follows exactly in the mirrors; forgetting height and weight limits; changing lanes without confirming the trailer has cleared.