District Of Columbia CDL Permit Test - Combination

When starting a trip, be sure that all shut-off valves are in the open position, except for the last valves on the rear trailer. It is important that air reaches the brakes on all trailers and that the air is not able to escape from the back of the vehicle.

Failure to keep the fifth wheel plate properly lubricated can create friction between the tractor and trailer, causing steering problems.

Combination vehicles have two air lines: a service line and an emergency line.

When driving a combination vehicle, it is important to brake well in advance and look far ahead of your vehicle to avoid the need for sudden stops. Making habits of these actions will help you prevent your trailer from jackknifing.

If the weight of a load is placed primarily one side of a trailer, the trailer may lean, increasing the risk of a rollover.

If a parked trailer does not have spring brakes, wheel chocks should be used to prevent it from moving. Air brakes can only hold a parked trailer for as long as there is air pressure remaining in the air tanks, so wheel chocks will ensure safety.

Making a sudden lane change can be dangerous when driving a combination vehicle. Avoid the need to make a sudden lane change by looking down the road for upcoming obstacles that will require you to change lanes.