CDL Doubles and Triples Endorsement

Double and Triple Trailers Course

Linehaul/Doubles Drivers earn $63,833 according to Glass Door data. The CDL permit is the second step. This free online course is the the first. This section has information you need to pass the CDL knowledge test for driving safely with double and triple trailers. It tells about how important it is to be very careful when driving with more than one trailer; how to couple and uncouple correctly; and how to inspect doubles and triples carefully.

Test Your Knowledge: Double and Triple Trailer Endorsements Quiz

Transcription: Doubles and Triples

Doubles and triples endorsement. This section covers pulling double triple trailers, coupling and uncoupling, inspecting doubles and triples, and checking air brakes. The section has information you need to pass the CDL knowledge test for driving safely with double and triple trailers. It tells about how important it is to be very careful when driving with more than one trailer, how to couple and uncouple correctly and about inspecting doubles and triples carefully.

Pulling doubles and triples. Take special care when pulling two and three trailers. There are more things that can go wrong, and doubles and triples are less stable than other commercial vehicles. To prevent trailers from a lean over, you must steer gently and go slowly around corners on ramps, off ramps, and curves. A safe speed on a curve for a straight truck or a single trailer combination may be too fast for a set of doubles or triples. Doubles and triples are more likely to turn over than other combination vehicles because of the crack-the-whip effect. You must steer gently when pulling trailers. The last trailer in a combination is most likely to turn over.

Inspect completely. There are more critical parts to check when you have two or three trailers. Check them all. Follow the procedures described later in the section. Doubles and triples must be driven very smoothly to avoid rollover or jackknife. Therefore, look far ahead so you can slow down or change lanes gradually when necessary.

Doubles and triples take up more space than other commercial vehicles. They're not only longer but also need more space because they can't be turned or stopped suddenly. Allow more following distance. Make sure you have large enough gaps before entering or crossing traffic. Be certain you are clear at the sides before changing lanes.

Be more careful in adverse conditions. In bad weather, slippery conditions and mountain driving, you must be especially careful if you drive double and triple bottoms. You have greater length than more dead axles to pull with your drive axles than other drivers. There is more chance for skids and loss of traction.

Parking the vehicle. Make sure you do not get into a spot where you cannot pull straight through. You need to be aware of how parking lots are arranged in order to avoid a long and difficult escape.

Anti-lock braking systems on converter dollies. Converter dollies built on or after March 1, 1998, are required to have anti-lock brakes. These dollies will have a yellow lamp on the left side of the dolly.

Coupling and uncoupling. Knowing how to couple and uncouple correctly is basic to safe operation of doubles and triples. Wrong coupling and uncoupling can be very dangerous. Coupling and uncoupling steps for doubles and triples are listed in the next section.

Coupling twin trailers. If the second trailer doesn't have spring brakes, drive the tractor close to the trailer, connect the emergency line, charge the trailer air tank, and disconnect the emergency line. This will set the trailer emergency brakes if the slack adjusters are correctly adjusted. Chock the wheels if you have any doubt about the brakes. For the safest handling on the road, the more heavily loaded semitrailer should be in first position behind the tractor. The lightest trailer should be in the rear. A converter gear on a dolly is a coupling device of one or two axles and a fifth wheel by which a semitrailer can be coupled to the rear of a tractor-trailer combination forming a double bottom rig.

Position the converter dolly in front of second or rear trailer. Release the dolly brakes by opening the air tank petcock. Or, if the dolly has spring brakes, use the dolly parking brake control. If the distance is not too great, wheel the dolly into position by hand so it is in line with the kingpin, or use the tractor and first semitrailer to pick up the converter dolly.

Position the combination as close as possible to the converter dolly. Move dolly to the rear of first semitrailer and couple it to the trailer. Lock the pintle hook. Secure the dolly support in a raised position. Pull dolly into position as close as possible to the nose of the second semitrailer. Lower the dolly support. Unhook the dolly from the first trailer. Wheel the dolly into position in front of the second trailer in line with the kingpin.

Connect the converter dolly to the front trailer. Back the first semitrailer into position in front of the dolly tongue. Hook the dolly to front trailer. Lock the pintle hook. Secure the converter gear support in raised position.

Connect the converter dolly to the rear trailer. Make sure trailer brakes are locked and/or the wheels chocked. Make sure the trailer height is correct. It must be slightly lower than the center of the fifth wheel, so the trailer is raised slightly when the dolly is pushed underneath. Back the converter dolly under the rear trailer. Raise the landing gear slightly off the ground to prevent damage if the trailer moves.

Test the coupling by pulling against the pin of the second semitrailer. Make visual check of the coupling. No space between the upper and lower fifth wheel. The locking jaws are closed around the kingpin. Connect the safety chains, air hoses, and light cords. Close converter dolly air tank petcock and shut-off valves at the rear of the second trailer. Open the shut-off valves at rear of first trailer and on the dolly, if so equipped. Raise the landing gear completely. Charge trailer brakes, push in the air-supply knob, and check for air at the rear of the second trailer by opening the emergency line shut-off. If air pressure isn't there, something is wrong and the brakes won't work.

Uncoupling twin trailers. Uncouple the rear trailer. Park the rig in a straight line on firm level ground. Apply the parking brakes so the rig won't move. Chock the wheels of second trailer if it doesn't have spring brakes. Lower the landing gear of the second semitrailer enough to remove some weight from the dolly. Close air shut-offs at rear of first semitrailer and on the dolly, if so equipped. Disconnect all dolly air and electric lines and secure them. Release the dolly brakes. Release the converter dolly fifth wheel latch. Slowly pull the tractor, first semitrailer, and dolly forward to pull the dolly out from underneath the rear semitrailer.

Uncouple the converter dolly. Lower the dolly landing gear. Disconnect the safety chains. Apply the converter gear spring brakes or chock wheels. Release the pintle hook on the first semitrailer. Slowly pull clear of the dolly. Never unlock the pintle hook with the dolly still underneath the trailer. The dolly tow bar may fly up, possibly causing injury, and making it very difficult to re-couple.

Coupling and uncoupling triple trailers. Couple the tractor first semitrailer to the second and third trailers. Couple the tractor to the first trailer. Use the method already described for coupling tractor semitrailers. Move the converter dolly into position and couple the first trailer to the second trailer using the method for coupling doubles. The triple's rig is now complete.

Uncouple the triple-trailer rig. Uncouple the third trailer by pulling the dolly out, then unhitching the dolly using the method for uncoupling doubles. Uncouple the remainder of the rig as you would any double-bottom rig using the method already described.

Coupling and uncoupling other combinations. The methods described so far apply to the more common tractor-trailer combinations. However, there are other ways of coupling and uncoupling the many types of truck-trailer and tractor-trailer combinations that are in use. There are too many to cover in this section. You will need to learn the correct way to couple and uncouple the vehicles you will drive according to the manufacturer and/or owner's specifications.

Inspecting doubles and triples. Use the seven-step inspection procedure to inspect your combination vehicle. There are more things to inspect on a combination vehicle than on a single vehicle. Many of these items are simply more of what you would find on a single vehicle, for example, tires, wheels, lights, and reflectors. However, there are also some new things to check. These are discussed next.

Additional checks, coupling system areas. Check the lower fifth wheel. It is securely mounted to the frame. No missing or damaged parts. There is enough grease. There is no visible space between the upper and lower fifth wheel. The locking jaws are around the shank and not the head of the kingpin. The release arm is properly seated and safety latch or lock is engaged. Check the upper fifth wheel. The glide plate is securely mounted to the trailer frame. The kingpin is not damaged.

Air and electric lines to trailer. Check that the electrical cord is firmly plugged in and secured. Air lines properly connected to glad hands. There are no air leaks. They are properly secured with enough slack for turns. All lines free from damage.

A sliding fifth wheel. The slide is not damaged or have missing parts. It is properly greased. All locking pins are present and locked in place. If air powered, there are no air leaks. Check that the fifth wheel is not so far forward that the tractor frame will hit the landing gear, or the cab will hit the trailer, during turns. The landing gear is fully raised. It has no missing parts, is not bent or otherwise damaged. The crank handle is in place and secured. If power operated, there are no air or hydraulic leaks.

Double and triple trailers. Check the shut-off valves at the rear of trailer. The front trailer, the valves are open. The rear of the last trailer, they are closed. The converter dolly air tank valve should be closed. Be sure air lines are supported and glad hands are properly connected. If a spare tire is carried under the converter dolly, make sure it is secured. Be sure the pintle-eye of the dolly is in place in the pintle hook of the trailers. Make sure the pintle hook is latched. Safety chains should be secured to the trailers. Make sure the light cords are firmly in the sockets on both trailers.

Check the air brakes on a double or triple trailer as you would any combination vehicle. You must also make the following checks on your double or triple trailers.

Check that air flows to all trailers. Use the tractor parking brake and/or chock the wheels to hold the vehicle. Wait for air pressure to reach normal, and then push in the red "trailer air supply" knob. This will supply air to the emergency supply lines.

Use the trailer handbrake to provide air to the service line. Go to the rear of the truck. Open the emergency line shut-off valve at the rear of the last trailer. You should hear air escaping, showing the entire system is charged. Close the emergency line valve. Open the service line valve to check that service pressure goes through all the trailers. This test assumes that the trailer handbrake or the service brake pedal is on, and then close the valve. If you do not hear air escaping from both lines, check that the shut-off valves on the trailer and dollies are in the open position. You must have air all the way to the back for all the brakes to work.

Test the tractor protection valve. Charge the trailer air brake system. That is, build up normal air pressure and push the "air supply" knob in. Shut the engine off. Step on and off the brake pedal several times to reduce the air pressure in the tanks. The trailer air supply control, also called the tractor protection valve control, or trailer emergency valve, and place it in the emergency position. Pull gently on the trailer with the tractor to check that the trailer emergency brakes are on.

Test the trailer service brakes. Check for normal air pressure, release the parking brakes, move the vehicle forward slowly, and apply their trailer brakes with the hand control or trolley valve. You should feel the brakes come on. This tells you the trailer brakes are connected and working. The trailer brakes should be tested with the hand valve, but controlled in normal operation with the foot pedal, which applies air to the service brakes at all wheels.