Ohio CDL: Combination Vehicles Practice Test

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 check the air line connections.

If you cross the emergency and service air lines, air will flow to the service line instead of the trailer air tanks. Air won't be available to release the spring brakes. Therefore, if the spring brakes don't release when you push the trailer air supply control, check the air line connections.

Not quite. The answer is slightly raised.

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 Both (a) and (c)

When the full weight of the trailer is resting on the tractor, check for enough clearance between the landing gear and the rear of the tractor frame. (When the tractor turns sharply, it must not hit the landing gear.) Also check for enough clearance between the tops of the tractor tires and the nose of the trailer. (When the tractor turns sharply, the front part of the trailer must not hit the tractor's tires.)

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 a fully loaded trailer

Trucks brake best when they are used as they were designed: to carry a properly balanced load. Empty trucks actually have longer stopping distances than loaded trucks because they have less traction. The stiff suspension springs and strong brakes give poor traction and make it easier to lock the wheels.

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 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 service and emergency air lines from the truck or tractor to the trailer.

Each glad hand has a rubber seal to prevent air from escaping. To connect the glad hands, first clean the seals. Then press the two seals together with the glad hands at a 90-degree angle to each other.

Not quite. The answer is Apply and release the trailer service brakes while you listen for sounds.

If you cross the air lines, supply air will be sent to the service line instead of the supply line and the trailer air tanks. Without a supply of air, the trailer service brakes won't work. Therefore, to make sure that the air lines aren't crossed, send air to the trailer brakes by pushing in the trailer air supply control (red knob). Let the pressure normalize. Then turn off the engine and try the trailer brakes. You should see and hear the brakes in action and then see the air pressure normalize again.

Not quite. The answer is Rear

The shut-off valve should be closed only at the rear of the last trailer so that air will flow to the brakes of all trailers but no farther.

Not quite. The answer is the coupling is not right and should be fixed before you drive the coupled unit.

Don't drive the vehicle until you're sure that the coupling is correct. Check to make sure of the following: There is no space between the upper and lower fifth wheel, the fifth wheel jaws have closed around the shank of the kingpin, the locking lever is in the "lock" position, and the safety latch is in position over the locking lever. If anything isn't right, don't drive the vehicle until you've found and corrected the problem. If you drive it anyway, your trailer could come loose while you're driving.

Not quite. The answer is go slowly around turns.

Because of rearward amplification, a trailer is more likely to roll over than a tractor. And if you're pulling doubles or triples, the rearmost (last) trailer is even more likely to roll over. To reduce the risk of trailer rollover, steer gently and smoothly, especially if you're pulling a double or triple. Slow down before entering a curve or turn.

Not quite. The answer is makes firm contact with the ground and takes some weight off the tractor.

When uncoupling a loaded trailer, 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 tractor, 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 next time.

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 Nothing is likely to happen until you try to apply the brakes.

If a leak has developed in the service line, air tank pressure may remain close to normal – until you try to brake. Then the air loss from the leak will cause the air pressure to drop quickly. If the air pressure drops far enough, the emergency brakes will come on.

Not quite. The answer is When you lock the drive wheels on the tractor and the tractor spins out sideways as the trailer continues to push forward

A jackknife is usually the result of a drive-wheel skid. The tractor's rear drive wheels lock, and the trailer starts to push the tractor sideways.

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 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.

Not quite. The answer is Control line and signal line

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