Alabama CDL: Combination Vehicles Practice Test

Not quite. The answer is to the driver's side.

If you must back your vehicle on a curved path, back toward the driver's side. You'll be able to watch the rear of your vehicle from your driver's-side window.

Not quite. The answer is over the locking lever.

The safety latch should be in position over the fifth wheel locking lever. On some vehicles, you may have to position it manually.

Not quite. The answer is if the air supply leaks away, there will be no brakes.

If the trailer lacks spring brakes, make sure you chock the wheels whenever you park. If air pressure leaks away, the trailer's brakes will fail. Without chocks, the trailer could roll away.

Not quite. The answer is supply air to the trailer system and then pull out the air supply knob.

Before backing under the trailer, check that the trailer brakes are working and then lock the trailer brakes. Once you've attached the air lines, there are a number of checks you should make: Check the glad hand seals. Make sure that the air lines won't be caught or crushed when you back under the trailer. Charge the trailer air brake system and verify that it's working without significant air loss. Then set the trailer air supply control to shut off the air and put on the trailer emergency brakes.

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 The trailer emergency brakes will come on.

The trailer air supply valve (which is manually controlled by the red dashboard knob) senses air pressure in the supply (emergency) line. If air pressure in the supply line is lost, the trailer air supply valve will close automatically, and the resulting loss of air pressure in the tractor protection valve will cause it to close as well. And loss of pressure in the supply line will cause the trailer emergency (spring) brakes to come on.

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 The rear wheels of the last trailer

Off-tracking is defined as the different paths taken by the front and rear wheels in a turn. The longer the vehicle, the greater the difference will be. Thus, the wheels on the front trailer will offtrack more than the tractor's rear wheels, and the wheels on the rearmost trailer will offtrack most of all.

Not quite. The answer is Yes, if you're not sure of your path of travel.

Backing a combination vehicle is potentially hazardous. Before you start to back up, check your intended path of travel. Exit the cab and walk around the vehicle. Check your clearance to the sides and overhead, in and near the path of your vehicle.

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

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 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 Never

The trailer hand valve (also known as a trolley valve or Johnson bar) controls only the trailer brakes, not the tractor brakes. You can use it to test the trailer brakes. But don't use it as a parking brake, especially if the trailer lacks spring brakes. If a leak causes loss of air pressure, the trailer brakes will fail. Don't use the trailer hand valve while you're driving either. Braking the trailer and not the tractor can cause the trailer to skid.

Not quite. The answer is trailer emergency brakes to come on.

If air pressure in the emergency air line drops too low (say because of a bad leak in the service line), the trailer emergency brakes will come on. Also, the tractor protection valve will close to keep air from escaping from the tractor.

Not quite. The answer is red; blue

To keep the air lines from being mismatched, they can be labeled with metal tags or color coded. Blue is used for the service lines, and red is used for the emergency lines. Couple the air lines of the same color.

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 To engage the trailer brakes in case of air pressure loss

The emergency air line has two main functions: (1) It supplies air to the trailer air tanks to keep the trailer brake system charged. (2) It controls the vehicle's emergency brakes. If air pressure in the emergency air line drops too low (say because of a bad leak or damage due to the trailer breaking loose), the trailer emergency brakes will come on. Also, the tractor protection valve will close to keep air from escaping from the tractor.

Not quite. The answer is the brakes on the trailer wheels caused the skid in the first place.

The trailer hand valve (also known as a trolley valve or Johnson bar) controls only the trailer brakes, not the tractor brakes. If you're already jackknifing because the trailer wheels locked up, applying the trailer brakes with the hand valve can make it even worse. Instead, stop braking. The rear wheels will start to roll again and you can steer to correct the skid.

Not quite. The answer is tilted down toward the rear of the tractor.

Before coupling, make sure that the fifth wheel is in the proper position. For one thing, it should be tilted down toward the rear of the tractor.

Not quite. The answer is 20 to 45 psi.

The tractor protection valve is located in the tractor, usually at the rear of the cab. Its purpose is to keep air in the tractor's air brake system should the trailer break away or develop a bad leak. The tractor protection valve is designed to close automatically if the air pressure falls into the range specified by the manufacturer, typically 20–45 psi.

Not quite. The answer is None

If there is space between the lower and upper fifth wheel after you have finished coupling, something is wrong. Perhaps the kingpin is on top of the closed fifth-wheel jaws, which could result in the trailer coming loose. Don't start to drive until you have identified and fixed the problem.