Iowa CDL: Double & Triple Trailers Practice Test

Not quite. The answer is Uncouple the third semitrailer from the second dolly.

To couple a triple-trailer combination, you couple the tractor and first semitrailer to the second and third semitrailers. But to uncouple the triple-trailer combination, you start by just uncoupling the third semitrailer from the rest of the combination.

Not quite. The answer is a coupling device that connects a semitrailer to the rear of a tractor-trailer.

The converter dolly connects a semitrailer to the rear of a tractor-trailer, forming a double or triple combination.

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 supply air to the trailer air brake system with the tractor and then disconnect the emergency line.

If the second trailer lacks spring brakes, set the emergency brakes or chock the wheels.

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 Open the air tank petcock.

You release the dolly's brakes by opening the air tank petcock or (if the dolly is equipped with spring brakes) using the dolly's parking brake control.

Not quite. The answer is Allow a greater following distance than for smaller commercial vehicles.

Doubles and triples need more space because they can’t be turned or stopped suddenly. Allow a greater following distance behind the vehicle in front of you.

Not quite. The answer is The rig may jackknife.

Check your mirrors to monitor your trailers and see if a trailer has begun to skid. Do this every time you have to brake hard. Once the wheels of a trailer begin to skid, the risk of jackknifing is high. Once the trailer swings out of your lane completely, you may not be able to prevent a jackknife.

Not quite. The answer is A sudden movement with the steering wheel can result in a tipped-over rear trailer.

Because of rearward amplification (the "crack-the-whip" effect), the rearmost trailer is much more prone to rolling over. Avoid sudden steering changes that could cause the rearmost trailer to roll over.

Not quite. The answer is using the dolly's parking brake control.

To connect the converter dolly to the first semitrailer, release the dolly's brakes so it can be moved. You release the dolly's brakes by opening the air tank petcock (valve) or using the dolly's parking brake control if the dolly is equipped with spring brakes.

Not quite. The answer is Brake and downshift in the curve.

Before entering a curve, slow down to a safe speed and downshift into the right gear. This lets you use some power through the curve to help keep the vehicle stable through the curve. It also allows you to speed up as soon as you are out of the curve.

Not quite. The answer is The more sharply you turn, the greater the chances of a skid or rollover.

Don't turn any more than needed to clear whatever is in your way. The more sharply you turn, the greater the chances of a skid or rollover.

Not quite. The answer is You must drive a double or triple very smoothly to avoid a rollover or jackknife.

Take special care when pulling two or three trailers. Doubles and triples are more likely to turn over than other combination vehicles because of the "crack-the-whip" effect. You must steer gently when pulling trailers. To prevent the trailers from rolling over, you must steer gently and go slowly around corners, on-ramps, off-ramps, and curves.

Not quite. The answer is Overloaded front axles can make the steering axle weight too light to steer safely.

Underloaded front axles (caused by shifting weight too far to the rear) can make the steering axle weight too light to steer safely.

Not quite. The answer is open the shut-off valves at the rear of the first trailer and close the shut-off valves at the rear of the second trailer.

Air must travel through the air lines of the tractor and all trailers – and that's all. Open the shut-off valves at the rear of each trailer but the last one to enable the air to travel to the trailer behind it. Close the shut-off valves at the rear of the last trailer to keep air from escaping.

Not quite. The answer is 5

In this context, articulation or pivoting means movement between two units separated by a joint, such as between a tractor and a trailer. A triple combination has 3 semitrailers connected with 2 converter dollies. This combination has 5 points of articulation: (1) the fifth wheel of the tractor; (2) the pintle hook of the first trailer; (3) the fifth wheel of the first converter dolly; (4) the pintle hook of the second trailer; and (5) the fifth wheel of the second converter dolly.

Not quite. The answer is directly in front of the converter dolly.

Back the first trailer into position in front of the tongue of the dolly. Hook the dolly to the pintle hook on the first trailer. Then latch the pintle hook securely. Raise the dolly's landing gear.

Not quite. The answer is The dolly tow bar may fly up.

If you unlock the pintle hook while the dolly is still underneath the rear trailer, the dolly's tow bar may fly up, making it harder to recouple and possibly injuring someone.

Not quite. The answer is use controlled or stab braking.

Hard braking and turning at the same time is likely to cause a skid. You should brake in a way that will keep your vehicle in a straight line and allow you to turn if necessary. If you need to brake suddenly to avoid a crash, use controlled braking or stab braking (but don't use stab braking if your vehicle has antilock brakes).

Not quite. The answer is sometimes lack antilock brakes.

All trailers and converter dollies built since March 1, 1998 are required to have antilock brakes (ABS).