Kentucky CDL: Combination Vehicles Practice Test

Not quite. The answer is Adjust the air supply knob to send air to the trailer brakes. Turn off the engine once the air pressure normalizes. Then listen for the sound of escaping air as the brakes are released.

After coupling, make sure that the air lines are not crossed. To do this, send air to the trailer brakes by adjusting the "air supply" knob to normal. Let the pressure normalize. Then turn off the engine and test the brakes. You should see and hear the brakes in action and then see the air pressure normalize again.

Not quite. The answer is It will keep dirt and water out of the lines.

Some vehicles are equipped with "dead-end" or dummy couplers. When the air lines are not connected to a trailer, connect the glad hands to the dummy couplers to keep water and dirt out of the glad hands and air lines. If your vehicle doesn't have dummy couplers, you may be able to connect the glad hands to each other.

Not quite. The answer is the brakes will fail if the air supply leaks away.

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 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 the emergency and service air lines.

Before backing under the trailer, you must lock the trailer brakes – which means that you first have to make sure that the trailer brakes are working. Connect the emergency and service air lines and test the trailer brakes.

Not quite. The answer is Gently pull forward in low gear against the locked trailer brakes; then look at it carefully.

After you've backed under the trailer and locked the kingpin into the fifth wheel, raise the landing gear slightly. Then with the trailer brakes still locked, gently pull the tractor forward to check that the trailer is locked onto the tractor.

Not quite. The answer is Always

If there is a leak in the emergency air line, air will eventually leak out of the trailer air tank. If the trailer has air brakes but not spring brakes, the brakes will fail. Use chocks to prevent the trailer from rolling if its brakes fail.

Not quite. The answer is get away from your vehicle and call 911 or the posted emergency number.

A train traveling at 60 mph can take more than a mile to come to a complete stop. If your vehicle gets stuck on a railroad track, don't spend any time trying to free your vehicle. Get out of your vehicle and walk quickly at about a 45-degree angle to the tracks in the direction from which you expect trains to approach. That way, if your vehicle is hit, you won't be struck by flying debris. Call 911 or the telephone number on the railroad crossing sign for assistance.

Not quite. The answer is On the left front or left rear corner

On a trailer, the yellow ABS malfunction lamp is located on the left front or left rear corner. Make sure you know where to look for it.

Not quite. The answer is often do not have spring brakes.

Trailers and converter dollies built before 1975 are not required to have spring brakes. Instead, they rely on emergency brakes that hold using air pressure. Because air pressure can leak away, always use wheel chocks when parking such vehicles.

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 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 Kentucky's requirements by contacting the Kentucky Transportation Cabinet or visiting their webpage "Overweight/Over-Dimensional Services" (https://drive.ky.gov/motor-carriers/Pages/OWOD-Services.aspx). [49 CFR 393.11],

Source: 49 CFR 393.87

Not quite. The answer is to test the trailer brakes.

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. Don't use it while you're driving, though. If you apply it while you're driving, you'll brake the trailers but not the tractor, which can cause a skid. Instead, use the foot brake, which sends air to the tractor brakes as well as the trailer brakes.

Not quite. The answer is back up gently to ease pressure on the fifth wheel locking jaws.

When uncoupling, ease pressure on the fifth wheel locking jaws by backing up gently. (This will help you release the fifth wheel locking lever.) Then apply the parking brakes while the tractor is pushing against the kingpin.

Not quite. The answer is your brakes might fail.

On a combination vehicle, the brakes on the tractor and all trailers must work properly. If your combination vehicle is equipped with air brakes, check that air flows to all trailers and test both the trailer service brakes and the trailer emergency brakes.

Not quite. The answer is It should not be done.

The trailer hand valve (also known as a spike, a trolley valve, or a 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 trailer skid.

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 It takes 14 seconds to clear a single track and more than 15 seconds to clear a double track.

You can expect it to take more than 15 seconds for a typical tractor-trailer to clear a double track and at least 14 seconds to clear a single track.

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 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.