Kansas CDL: Combination Vehicles Practice Test

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 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 trailer emergency brakes will come on.

If a major leak develops in the service line, you may not notice anything wrong – until you try to apply the service brakes. Then the air loss from the leak will lower the air tank pressure quickly. If it goes low enough, the trailer emergency brakes will come on.

Not quite. The answer is they are more likely to get stuck on raised railroad crossings.

The two types of combination vehicles most likely to get stuck at a raised railroad crossing are low-slung units (car carriers, lowboys, moving vans, etc.) and single-axle tractors that are pulling a long trailer with its landing gear set to accommodate a tandem-axle tractor. Be very careful when driving such vehicles at railroad crossings.

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 low gear.

Start to raise the landing gear by using the low gear range (if the landing gear is so equipped). Then switch to the high gear range once the trailer supports are free of weight.

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 No, because the brakes on the trailer wheels caused the skid to begin with.

The trailer skid was caused by the brakes locking the wheels. Applying the trailer hand brake might make that even worse. Instead, release the brakes so the trailer wheels can roll again and regain traction.

Not quite. The answer is pushing in the trailer air supply control.

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.

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 a yellow malfunction lamp on the left side.

A trailer with ABS has a yellow malfunction lamp on either the left front corner or the left rear corner. Make sure you know where to look for it.

Not quite. The answer is release the brakes.

Once you realize your vehicle is in a skid, you should release the brakes so that the wheels can grip the road again. The trailer will start to follow the tractor and straighten out.

Not quite. The answer is If you make a quick lane change or sudden movement of your steering wheel, your trailers will tend to swing out. The rearmost trailer will swing out the most and will be most likely to roll over.

A sudden maneuver by the tractor may cause the rearmost (last) trailer to swing violently and possibly roll over. This is known as the crack-the-whip effect. It is caused by rearward amplification: The farther a trailer is from the tractor, the more likely it is to start swinging dangerously out of control.

Not quite. The answer is 10

The recommended formula for following distance is one second per ten feet of vehicle length, plus an extra second if you're traveling over 40 mph.

Not quite. The answer is more

There are more things to inspect on a combination vehicle than on a bus or straight truck. First, of course, there is the entire coupling system: the kingpin, the fifth wheel, etc. Next, there is the landing gear of each trailer. Finally, the air brake system is also more complicated than on a bus or straight truck, because compressed air must flow to all trailers so that both the tractor brakes and trailer brakes will work properly.

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).

Not quite. The answer is Pull the tractor ahead gently with the trailer brakes locked.

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 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 Drive normally and get it fixed later.

Losing the ABS function does not change the basic parts of your truck, so you will still have the same brakes that you have always had. Simply use them and get the ABS repaired as soon as possible. There is no need to panic, unless your system shows other and more serious warnings.

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.