Iowa CDL: Combination Vehicles Practice Test

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 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 The shank

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 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 supply air to the trailer system and then pull out the air supply knob.

First, make sure that the trailer brakes are working properly. Before backing under the trailer, set the trailer air supply control to lock the trailer brakes. You do this by pulling out the red air supply knob (on newer vehicles) or moving the tractor protection valve control to the emergency setting.

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 at normal pressure.

Before backing under a trailer during the coupling process, make sure that the air pressure is at normal levels so you'll be able to brake safely.

Not quite. The answer is Bobtail tractors can take longer to stop than fully loaded combination vehicles.

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. Likewise, "bobtail" tractors (tractors without semitrailers) can take longer to stop than a fully loaded tractor-trailer. Be very careful when driving a "bobtail" tractor.

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 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 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 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 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 open except for those on the last trailer.

The shut-off valves are located at the rear of each trailer to allow you to stop the air flow there. If there is another trailer behind this one, open the valves to allow air to flow to that trailer; otherwise, close the valves.

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 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 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 Fully raised with the crank handle secured in its bracket

Once you've coupled, raise the landing gear all the way up. If it's only partially raised, it could catch on something, such as the railroad tracks on a raised railroad crossing.

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 so that the trailer can easily slide into it.

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.