Oregon CDL: Double & Triple Trailers Practice Test

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 Check for normal air pressure. Release the parking brakes. Pull forward slowly. Apply the trailer brakes, using the hand control if so equipped.

Checking your trailer's service brakes is a four-step process: 1. Check for normal air pressure. 2. Release the parking brakes. 3. Pull your vehicle forward slowly. 4. Apply the trailer brakes, using the hand control (trolley valve) if so equipped. If the trailer brakes are properly connected and working, you should feel them come on at this point.

Not quite. The answer is There are more critical parts to check.

There is nothing inherently wrong with double or triple trailers. There are just more critical parts to check. For a triple, you must check the critical parts of three trailers and two converter dollies, problems in any of which can cause serious trouble.

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).

Not quite. The answer is Neither of the above will cause it.

Despite what footnote 5 in 49 CFR 393.11 says, Operational Policy 15 of the North American Standard Out-of-Service Criteria states that a converter dolly must have one stop lamp, one tail lamp, and (if the dolly obscures the tractor's rear turn signals) turn signal lights, but only when the dolly is being towed singly and is not towing a trailer. In a full multi-trailer configuration, the rearmost trailer must have working stop lights and taillights, of course.

Not quite. The answer is Closed

A pre-trip inspection of a double or triple combination vehicle includes an inspection of each converter dolly. Among other things, check that the converter dolly air tank petcock is closed.

Not quite. The answer is You need about four times as much braking distance at 40 mph as at 20 mph.

Your total stopping distance is the sum of your perception distance (how far your vehicle goes from when you see the hazard until your brain processes it), reaction distance (how far the vehicle goes from when your brain orders your foot to take action until your foot actually starts to brake), and braking distance (how far the vehicle continues to travel once you apply the brake). Your vehicle's braking distance increases as the square of your speed. For example, you need about four times as much braking distance at 40 mph as you do at 20 mph.

Not quite. The answer is the trailer will be raised slightly when the converter dolly is backed under it.

To connect the rear trailer to the converter dolly, the trailer must be at the right height. It should be slightly lower than the center of the dolly's fifth wheel so that the trailer will be raised slightly when the dolly is pushed underneath it.

Not quite. The answer is rear.

Vehicles with double or triple trailers can experience a dangerous "crack-the-whip" effect, caused by rearward amplification. If you make a quick lane change, the crack-the-whip effect can turn the trailers over. (There have been many accidents where only the trailer overturned.) Rearward amplification is strongest at the rearmost trailer. Therefore, position your heaviest trailer at the front and your lightest trailer at the rear.

Not quite. The answer is enough to take some of the weight off the dolly.

When uncoupling a loaded second or third semitrailer, 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 dolly, 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 the trailer next time.

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 Open at the rear of the front trailers and closed at the rear of the last 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 flow 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 10

The formula for following distance is one second per ten feet of vehicle length, plus an extra second if you are traveling over 40 mph. Therefore, for a 100-foot vehicle traveling at 30 mph, you should leave a following distance of 100/10 = 10 seconds. (At or below 40 mph, you do not add an extra second.)

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 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 Slow to a safe speed before entering the curve, then accelerate slightly through it.

The safest way to take a curve is to slow down before the curve and then accelerate slightly through the curve. Braking in a curve risks a skid.

Not quite. The answer is Charge the trailer's air tank and then disconnect the emergency air line.

If the second trailer doesn’t have spring brakes, drive the tractor close to the trailer, connect the emergency line, charge the trailer air tank, and disconnect the emergency air line. This will set the trailer emergency brakes (assuming the slack adjusters are correctly adjusted). Chock the wheels if you have any doubt about the brakes.

Not quite. The answer is may be too fast for a set of doubles or triples.

On curves, doubles and triples are more likely to roll over than other combination vehicles. A safe speed on a curve for a straight truck or a single-trailer combination vehicle may be too fast for a set of doubles or triples. To prevent trailers from rolling over, you must steer gently and go slowly around corners, on-ramps, off-ramps, and curves.

Not quite. The answer is to lower its landing gear.

After you have uncoupled the rear trailer from the converter dolly, you need to uncouple the converter dolly from the front trailer. You do this as follows: 1. Lower the landing gear of the dolly. 2. Disconnect the safety chains. 3. Apply the dolly's spring brakes or chock its wheels to keep the dolly from moving. 4. Release the pintle hook connecting the dolly to the trailer ahead of it. 5. Slowly pull clear of the dolly.

Not quite. The answer is There should be none.

When the rear trailer is properly coupled to the converter dolly, there should be no space between the upper and lower fifth wheel. (Similarly, when the front trailer is properly coupled to the tractor, there should be no space between the upper and lower fifth wheel either.) If there is visible space, something is wrong. Don't drive the vehicle until you have corrected the problem because the trailer might come loose.