California CDL: Combination Vehicles Practice Test

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

With the loss of air pressure, the tractor protection valve will close and the trailer emergency brakes will come on.

Not quite. The answer is To prevent steering problems

One of the first steps in coupling a tractor to a trailer is to check that the fifth wheel skid plate is greased as required. If the fifth wheel plate is not properly lubricated, friction between the plate and the trailer apron could cause steering problems.

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 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 opening the emergency line shut-off valve and then the service line valve at the rear of the last trailer and listening for air escaping each time.

To check whether air is flowing to all trailers, go to the rear of the last trailer and open the emergency line shut-off valve there. If the entire system is charged, you should hear air escaping. Then close that valve and open the service line valve. Again, you should hear air escaping.

Not quite. The answer is you might make the trailer skid.

You should use the hand valve only when you are testing the brakes. If you use it while driving the vehicle, you run a high risk of skidding. The foot brake is a much safer method of braking and is much less likely to cause skidding and jackknifing.

Not quite. The answer is Pressing the pedal several times to lower the air pressure

Checking that air is flowing to all trailers does not involve pressing the pedal several times to lower the air pressure. In fact, the air pressure should be normal when you push in the "trailer air supply" knob. Instead, go to the rear of the last trailer and open the emergency line shut-off valve. If air is flowing to all trailers, you should hear air escaping.

Not quite. The answer is two red lights

According to federal regulations, if the load projects more than 4 feet behind the rear of the vehicle, the end of the load must be marked as follows: (1) with two red flags, each 18 inches square, in the daytime; or (2) with two red lights at night. There are additional federal requirements on how to illuminate the rest of the load. US states may impose their own additional requirements on the transportation of oversized loads. You can learn about California's requirements by contacting Caltrans or visiting their webpage "Transportation Permits (Oversize/Overweight Vehicles)" (https://dot.ca.gov/programs/traffic-operations/transportation-permits). [49 CFR 393.11],

Source: 49 CFR 393.87

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 of the danger of making the trailer skid.

The trailer hand valve (also known as a trolley valve or Johnson bar) controls only the trailer brakes, not the tractor brakes. If you apply it while you're driving, you'll brake the trailers but not the tractor. This can cause a skid or even a jackknife. Instead, use the foot brake, which sends air to the tractor brakes as well as the trailer brakes.

Not quite. The answer is Upper and lower fifth wheel, air lines, and electrical lines

When making a visual check of the coupling, be sure to check the upper and lower fifth wheel, air lines, and electrical lines.

Not quite. The answer is Control line and signal line

The service air line is also known as the control line or signal line.

Not quite. The answer is easier it is to turn over.

When you stack cargo high in a trailer, you raise its center of gravity, which makes the trailer more prone to rolling over. A fully loaded tractor-trailer is ten times more likely to roll over in a crash than an empty one.

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 keep the trailer from moving.

In the absence of spring brakes, chocks help keep the trailer from moving. You should never use the hand brake when parking, so use either the parking brakes or chocks.

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 the coupling surface of the trailer is just below the middle of the tractor fifth wheel.

The tractor fifth wheel should tilt downward toward the trailer. As you start to back the tractor under the trailer, the coupling surface of the trailer should be just below the middle of the tractor fifth wheel.

Not quite. The answer is a Class A CDL with a Doubles/Triples (T) endorsement.

To legally pull a trailer whose gross vehicle weight rating (GVWR) exceeds 10,000 pounds, you'll have to obtain a Class A CDL. To pull triples, you'll also have to obtain a Doubles/Triples (T) endorsement on your CDL. Note: If you don't also pass a knowledge test on air brakes, your CDL will include a restriction limiting you to driving only vehicles without air brakes.

Not quite. The answer is Normal

To test the trailer air brake system, first charge it with air. To do this, push in the red trailer air supply knob, or (in older vehicles) move the tractor protection valve control from the "emergency" position to the "normal" position. Wait until the air pressure reaches normal before you check for crossed air lines.

Not quite. The answer is step on and off the brake pedal several times.

To test the tractor protection valve, charge the trailer air brake system, turn off the engine, and lower the air pressure by stepping on and off the brake pedal several times. The tractor protection valve control (also called the trailer air supply control) should pop out (or go from the “normal” to the “emergency” position) when the air pressure falls into the range specified by the manufacturer (typically 20–45 psi).