Wyoming CDL: Double & Triple Trailers Practice Test

Not quite. The answer is slow down.

You should always be able to stop within the distance you can see ahead. Your low-beam headlights let you see only about 250 feet ahead. At 55 mph, your vehicle will travel 250 feet in just 3.1 seconds – not enough time to notice and safely avoid a hazard that's within 250 feet of you. At 30 mph, your vehicle will travel 250 feet in 5.7 seconds.

Not quite. The answer is a separate air tank.

Federal regulations require brakes on every wheel of a combination vehicle, including the wheels of the semitrailers and converter dollies. Like semitrailers, dollies have their own air brakes and their own air tanks.

Source: 49 CFR § 393.42

Not quite. The answer is a coupling device that connects a semitrailer to the rear of a tractor-trailer.

The converter dolly connects a semitrailer to the rear of a tractor-trailer, forming a double or triple combination.

Not quite. The answer is Older models may lack spring brakes.

All converter dollies built since 1975 are required to have spring brakes. All converter dollies built since 1998 are required to have antilock brakes as well.

Not quite. The answer is 20 to 45 psi.

The tractor protection valve keeps air in the tractor or truck brake system should the trailer break away or develop a bad leak. The tractor protection valve is designed to close automatically when the air pressure falls into the range specified by the manufacturer, typically 20–45 psi.

Not quite. The answer is to lower its landing gear.

After you have uncoupled the rear trailer from the converter dolly, you need to uncouple the converter dolly from the front trailer. You do this as follows: 1. Lower the landing gear of the dolly. 2. Disconnect the safety chains. 3. Apply the dolly's spring brakes or chock its wheels to keep the dolly from moving. 4. Release the pintle hook connecting the dolly to the trailer ahead of it. 5. Slowly pull clear of the dolly.

Not quite. The answer is Use wheel chocks.

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 (assuming the slack adjusters are correctly adjusted). However, if you have any doubt about the effectiveness of the trailer's braking system, chock the wheels.

Not quite. The answer is slowly pull clear of the converter dolly.

The last step in the process of uncoupling twin trailers is to slowly pull clear of the converter dolly. The other two choices are previous steps in this process.

Not quite. The answer is air escape from the open valve.

Test the trailer brakes by opening the service line valve at the rear of the rig. You should hear the telltale hiss of air escaping. If you don't, it means that air is not flowing through the entire line, and you will need to investigate.

Not quite. The answer is less

Double and triple vehicles are more prone to rolling over or jackknifing than single vehicles are. Avoid sudden braking or steering changes. Look far enough ahead that you can slow down or change lanes gradually when necessary.

Not quite. The answer is Brake and downshift in the curve.

Before entering a curve, slow down to a safe speed and downshift into the right gear. This lets you use some power through the curve to help keep the vehicle stable through the curve. It also allows you to speed up as soon as you are out of the curve.

Not quite. The answer is Use the engine brake or speed retarder.

A retarder supplements the braking force on the drive wheels. On a slippery surface, this may cause the wheels to lock, resulting in a skid. Turn off your retarder when driving on wet, icy, or snowy roads. Instead, slow down, increase your following distance, and try to brake gently.

Not quite. The answer is Doubles/triples flip over from quick steering movements more easily than do many other vehicles.

Because of rearward amplification (the "crack-the-whip" effect), steering changes affect the rearmost trailer much more than they affect the front trailer or the tractor. Avoid quick or sharp steering changes that could cause the rearmost trailer to roll over.

Not quite. The answer is A truck has less traction when it's empty than when it's fully loaded.

Trucks that are empty or only lightly loaded take longer to stop because the stiff suspension springs and strong brakes give poor traction and make it easier to lock the wheels.

Not quite. The answer is closed.

A pre-trip inspection of a double or triple combination vehicle includes an inspection of each converter dolly in the vehicle. Among other things, check that the converter dolly air tank drain valve is closed.

Not quite. The answer is enough to remove some of the trailer's weight from the converter dolly.

Lower the landing gear of the second semitrailer enough to remove some of the trailer's weight from the converter dolly. This will make it easier to pull the dolly out from under the trailer.

Not quite. The answer is Both (a) and (b)

Take special care when pulling two or three trailers. In bad weather, under slippery conditions, and in mountain driving, you must be especially careful. There is a greater risk of skids and loss of traction. Also, doubles and triples need more space because they can’t be turned or stopped suddenly. Maintain a greater following distance. Make sure you have large enough gaps before entering or crossing traffic.

Not quite. The answer is Pull against the rear semitrailer's pin.

To check the coupling of the rear semitrailer, pull against the pin holding the rear semitrailer. Never move your vehicle until you are sure that all trailers are properly coupled.

Not quite. The answer is rear.

Vehicles with double or triple trailers can experience a dangerous "crack-the-whip" effect, caused by rearward amplification. If you make a quick lane change, the crack-the-whip effect can turn the trailers over. (There have been many accidents where only the trailer overturned.) Rearward amplification is strongest at the rearmost trailer. Therefore, position your heaviest trailer at the front and your lightest trailer at the rear.

Not quite. The answer is enough to take some of the weight off the dolly.

When uncoupling a loaded second or third semitrailer, lower the landing gear until it makes firm contact with the ground. Then crank the landing gear in low gear for a few more turns – just enough to lift some weight off the dolly, but not so much that you lift the trailer off the fifth wheel. This will make it easier to unlatch the fifth wheel now and couple the trailer next time.