Maine CDL: Combination Vehicles Practice Test

Not quite. The answer is release the brakes.

Once you realize your vehicle is in a skid, you should release the brakes so that the wheels can grip the road again. The trailer will start to follow the tractor and straighten out.

Not quite. The answer is applying and releasing the trailer brakes and listening for brake sounds.

After you've connected the air lines, double-check the connection and make sure the brakes are working. Shut off the engine so you can hear the brakes. Apply the brakes and listen for the sound of the brakes being applied. Release the brakes and listen for the hiss of escaping air.

Not quite. The answer is To prevent steering problems

There shouldn't be any space between the upper and lower fifth wheel. However, friction could cause steering problems. To reduce friction, make sure that the fifth wheel plate is well lubricated as required.

Not quite. The answer is A 5-axle tractor towing a 52-foot trailer

When any vehicle turns, its rear wheels will follow a shorter path than its front wheels. This is called off-tracking or "cheating." The longer the vehicle, the greater the difference. In a combination vehicle, the trailer's wheels will off-track more than the tractor's rear wheels. In a double or triple combination vehicle, the wheels of the last trailer will off-track the most.

Not quite. The answer is pushing in the trailer air supply control.

On newer vehicles, the trailer air supply control is an eight-sided red knob on the dashboard of the tractor. The knob may be labeled "Pull to exhaust...Push to supply" or something similar. When you push the knob in, air will flow through the trailer's emergency air lines to charge the trailer air brake system.

Not quite. The answer is there is less traction.

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 A 3-axle tractor towing two 27-foot trailers

When any vehicle turns, its rear wheels will follow a shorter path than its front wheels. This is called off-tracking or "cheating." The longer the vehicle, the greater the difference. In a combination vehicle, the trailer's wheels will off-track more than the tractor's rear wheels. In a double or triple combination vehicle, the wheels of the last trailer will off-track the most.

Not quite. The answer is rollovers.

More than half of truck driver deaths in crashes are the result of truck rollovers. A full load increases the weight on the truck, making a jackknife less likely. But a full load also raises the truck's center of gravity, making a rollover more likely. Furthermore, many of America's expressways are old, with curved exit ramps that don't have the banking needed for today's combination vehicles.

Not quite. The answer is A tractor pulling three trailers

The last trailer of a triple is 3.5 times more likely to roll over than a five-axle tractor. This is known as the crack-the-whip effect. When pulling a triple, increase your following distance, avoid sudden moves, and steer gently. At night, don't drive faster than your headlight range.

Not quite. The answer is see it in your mirrors.

The earliest way to notice that your trailer is jackknifing is to see it swinging out in your mirrors.

Not quite. The answer is 3 psi per minute.

To test the static air leakage rate, turn off the engine, release the parking brake (i.e., push the parking brake control knob in), and see how fast the air pressure drops. The air pressure should drop less than 2 psi in one minute for a single vehicle and less than 3 psi in one minute for a combination vehicle.

Not quite. The answer is it will be raised slightly when the tractor is backed under it.

Before backing the tractor under the trailer, adjust the landing gear to position the trailer at the proper height. The trailer should be just low enough that it will be raised slightly by the tractor when the tractor backs under it. If the trailer is too low, the tractor may hit and damage the trailer nose; if it's too high, it may not couple properly.

Not quite. The answer is Turn wide as you complete the turn.

To turn right, you must turn wide to help prevent the rear end of your vehicle from overrunning the curb. However, if you swing wide to the left before you turn right, another driver may try to pass you on your right, which can lead to a collision. Instead, start the right turn with the rear of your vehicle as close to the curb as possible and then turn wide as you complete the turn. This will deny drivers room on the right to try to pass you.

Not quite. The answer is directly in front of the trailer.

When you're ready to couple, position your tractor right in front of the trailer. If you were to back into the trailer at an angle, you might push it sideways and break the landing gear.

Not quite. The answer is fully loaded

The weight of cargo helps the wheels get traction. When a combination vehicle is empty or lightly loaded, its braking distance increases. The very stiff suspension springs and strong brakes give poor traction and make it very easy to lock the wheels.

Not quite. The answer is hang it with the plug down.

After you disconnect the electrical cable, hang it with the plug down to keep moisture or rain from getting into it.

Not quite. The answer is B.

If you swing wide to the left before you turn right, another vehicle may try to pass you on your right while you are turning. Instead, as shown in path B, make the right turn with the rear of your vehicle as close to the curb as possible and turn wide as you complete the turn. This will deny other vehicles enough room on the right to try to pass you.

Not quite. The answer is The rear trailer is twice as likely to turn over as the tractor.

Because of rearward amplification, the last trailer on a combination vehicle has the highest probability of rolling over. This is called the crack-the-whip effect.

Not quite. The answer is It is used to supply the trailer with air, shut the air off, and apply the trailer emergency brakes.

On newer vehicles, the trailer air supply control is an eight-sided red knob on the dashboard of the tractor. The knob may be labeled "Pull to exhaust...Push to supply" or something similar. When you push the knob in, air will flow through the trailer's emergency air lines to charge the trailer air brake system. Pulling out the knob shuts off the flow of air and causes the trailer emergency brakes to come on.

Not quite. The answer is open

When uncoupling, unlock the fifth wheel by raising the release handle lock and pulling the release handle to the open position. When you do this, keep your legs and feet well clear of the tractor's rear wheels in case the vehicle moves.