Georgia CDL: Combination Vehicles Practice Test

Not quite. The answer is over the locking lever.

The safety latch should be in position over the fifth wheel locking lever. On some vehicles, you may have to position it manually.

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 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 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 Push in the trailer air supply valve control.

The control for the trailer air supply valve is an eight-sided red knob on the dashboard. You push the knob in to supply compressed air to the trailer air brake system. You pull the knob out to evacuate air from the trailer air brake system (which will set the trailer brakes).

Not quite. The answer is 4 psi per minute.

After the initial drop, the maximum acceptable leakage rates with the service brakes on are 3 psi per minute for single vehicles and 4 psi per minute for combination vehicles. If the leakage rate is higher, check for leaks and correct them.

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 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 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 emergency

The tractor protection valve keeps air in the tractor if the trailer breaks away or develops a bad leak. If air pressure drops too low in the service line, the tractor protection valve will close. This stops air from escaping from the tractor and lets air out of the trailer emergency line, causing the trailer emergency brakes to come on.

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 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 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 Georgia's detailed requirements by contacting the Georgia Department of Transportation or reviewing their webpage "Oversize Permits" (http://www.dot.ga.gov/PartnerSmart/permits/Pages/Oversize.aspx). [49 CFR 393.11],

Source: 49 CFR 393.87

Not quite. The answer is "Bobtail" tractors can take longer to stop than fully loaded tractor-trailers.

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 secured but with enough slack for turns.

During your walk-around inspection, make sure that the electrical and air lines are secure but have enough slack to stay attached and secure even when the vehicle is turning.

Not quite. The answer is A 3-axle tractor towing two 27-foot trailers

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 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 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 emergency line

The trailer air supply valve (which is manually controlled by the red dashboard knob) senses air pressure in the supply (emergency) line. If air pressure in the supply line is lost, the trailer air supply valve will close automatically, and the resulting loss of air pressure in the tractor protection valve will cause it to close as well. And loss of pressure in the supply line will cause the trailer emergency (spring) brakes to come on.

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 restriction L, limiting you to driving only vehicles without air brakes.