Connecticut CDL: Combination Vehicles Practice Test

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 Upper and lower fifth wheel, air lines, and electrical lines

When making a visual check of the coupling, be sure to check the upper and lower fifth wheel, air lines, and electrical lines.

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 trailer emergency brakes to come on.

With the loss of air pressure, the tractor protection valve will close and the trailer emergency brakes will come on.

Not quite. The answer is Yes, if you're not sure of your path of travel.

Backing a combination vehicle is potentially hazardous. Before you start to back up, check your intended path of travel. Exit the cab and walk around the vehicle. Check your clearance to the sides and overhead, in and near the path of your vehicle.

Not quite. The answer is In the rear

The shut-off valves are located at the rear of a trailer, since that is where they must be located to service the air lines. The shut-off valves are open except in the last trailer, in which they are closed.

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 Connecticut's detailed requirements by contacting the Connecticut Department of Transportation or reviewing their webpage "CTDOT Oversize/Overweight Permit Unit" (https://portal.ct.gov/DOT/Permits/Highways/OSOW - New). [49 CFR 393.11],

Source: 49 CFR 393.87

Not quite. The answer is open

When uncoupling, unlock the fifth wheel by raising the release handle lock and pulling the release handle to the open position. When you do this, keep your legs and feet well clear of the tractor's rear wheels in case the vehicle moves.

Not quite. The answer is the coupling surface of the trailer is just below the middle of the tractor fifth wheel.

The tractor fifth wheel should tilt downward toward the trailer. As you start to back the tractor under the trailer, the coupling surface of the trailer should be just below the middle of the tractor fifth wheel.

Not quite. The answer is A tractor pulling three trailers

The last trailer of a triple is 3.5 times more likely to roll over than a five-axle tractor. This is known as the crack-the-whip effect. When pulling a triple, increase your following distance, avoid sudden moves, and steer gently. At night, don't drive faster than your headlight range.

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 there is less traction.

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 The rear trailer is twice as likely to turn over as the tractor.

Because of rearward amplification, the last trailer on a combination vehicle has the highest probability of rolling over. This is called the crack-the-whip effect.

Not quite. The answer is get away from your vehicle and call 911 or the posted emergency number.

A train traveling at 60 mph can take more than a mile to come to a complete stop. If your vehicle gets stuck on a railroad track, don't spend any time trying to free your vehicle. Get out of your vehicle and walk quickly at about a 45-degree angle to the tracks in the direction from which you expect trains to approach. That way, if your vehicle is hit, you won't be struck by flying debris. Call 911 or the telephone number on the railroad crossing sign for assistance.

Not quite. The answer is The rear wheels of the last trailer

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. Thus, the wheels on the front trailer will offtrack more than the tractor's rear wheels, and the wheels on the rearmost trailer will offtrack most of all.

Not quite. The answer is Bobtail tractors can take longer to stop than fully loaded combination vehicles.

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 empty.

Trucks brake best when they are used as they were designed: to carry a properly balanced load. 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.

Not quite. The answer is it will be raised slightly when the tractor is backed under it.

Before backing the tractor under the trailer, adjust the landing gear to position the trailer at the proper height. The trailer should be just low enough that it will be raised slightly by the tractor when the tractor backs under it. If the trailer is too low, the tractor may hit and damage the trailer nose; if it's too high, it may not couple properly.

Not quite. The answer is The trailer emergency brakes will come on.

If the emergency (supply) air line breaks, the tractor protection valve will close to stop any more compressed air from leaving the tractor. Hence, the tractor's service brakes should still work. However, the loss of trailer air pressure from the ruptured line will cause the trailer emergency (spring) brakes to come on.

Not quite. The answer is A triple 27-foot trailer

Because of rearward amplification (causing the crack-the-whip effect), the last trailer in a combination vehicle has the highest probability of rolling over. The last trailer in a triple combination is more likely to roll over than the last trailer in a double combination.