Minnesota CDL: Double & Triple Trailers Practice Test

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.

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 make things look smaller and farther away than they really are.

A convex mirror has a wider field of view than a flat mirror. However, objects viewed in a convex mirror look smaller and farther away. Remember this when you're trying to judge the distance of an object that you're viewing in a convex mirror.

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 11

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 50 mph, you should leave a following distance of 100/10 + 1 = 11 seconds.

Not quite. The answer is Allow much more space than is needed under ideal driving conditions.

The usual formula for following distance under ideal conditions is one second for every ten feet of vehicle length, plus an extra second if you are traveling at over 40 mph. The only thing the CDL manual says about following distance on slippery roads is that you should allow "much more space to stop." The Federal Motor Carrier Safety Administration (FMCSA) recommends doubling your usual following distance under poor driving conditions.

Source: "CMV Driving Tips - Following Too Closely," FMCSA, https://www.fmcsa.dot.gov/safety/driver-safety/cmv-driving-tips-following-too-closely

Not quite. The answer is a yellow lamp on the left side.

A converter dolly with antilock brakes is required to have a yellow ABS lamp on its left side. All converter dollies built since March 1, 1998 have antilock brakes.

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 The pintle eye of the dolly should be in place in the pintle hook of the trailer.

A pre-trip inspection of a double or triple combination vehicle includes an inspection of each converter dolly in the vehicle. Among other things, check the coupling of the dolly to the trailer in front. Make sure that the pintle eye of the dolly is in place in the pintle hook of the trailer, and the pintle hook is latched closed.

Not quite. The answer is How the rear wheels follow a different path from the front wheels in a turn

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. As a result, the path followed by a tractor will be wider than the path of the rig itself. To compensate, you must steer the tractor wider to keep the rig from overrunning the curb or hitting some object.

Not quite. The answer is less

Double and triple vehicles are more prone to rolling over or jackknifing than single vehicles are. Avoid sudden braking or steering changes. Look far enough ahead that you can slow down or change lanes gradually when necessary.

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 apply light pressure on the brakes.

Avoid driving through deep puddles or flowing water if possible. If not, slow down and downshift into a low gear. Gently press on the brakes and maintain pressure for a short distance when you are out of the water. This will heat up the brakes and dry them out. (However, don't overdo it, or the brakes may overheat.) Then apply the brakes to make a test stop when it is safe to do so.

Not quite. The answer is 20 to 45 psi.

The tractor protection valve keeps air in the tractor or truck brake system should the trailer break away or develop a bad leak. The tractor protection valve is designed to close automatically when the air pressure falls into the range specified by the manufacturer, typically 20–45 psi.

Not quite. The answer is Rocky Mountain double

A double pup trailer consists of two 28.5-foot trailers, known as "pup trailers." A double pup trailer is also known as an STAA trailer, named for the Surface Transportation Assistance Act (STAA). This standard-double configuration is the only type of double trailer that is allowed nationwide. A Rocky Mountain double trailer consists of a 40- to 53-foot trailer followed by a 28.5-foot pup trailer. Rocky Mountain doubles are allowed in certain Western states. A turnpike double trailer consists of two 48-foot trailers. Turnpike doubles can be found traveling on expressways in the Eastern states.

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 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 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 A truck has less traction when it's empty than when it's fully loaded.

Trucks that are empty or only lightly loaded take longer to stop because the stiff suspension springs and strong brakes give poor traction and make it easier to lock the wheels.

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.