Combination Questions & Answers

Question 1

1. The “crack-the-whip” effect can:

Answer 1

› Turn over a trailer.
Trailers can overturn as a result of the “crack-the-whip” effect. The last trailer in a
combination is the most prone to tip over due to this effect. Drivers should be aware of the
rearward amplification of their specific vehicles and drive accordingly.

Question 2

2. To help prevent rollovers, you should:

Answer 2

› Drive slowly around turns.
To lower the risk of a rollover, load your cargo as closely to the ground as possible. To further
reduce this risk, take curves and corners slowly.

Question 3

3. Large combination vehicles take the longest amount of time to stop:

Answer 3

› When empty.
Large combination vehicles take longer to stop when they are empty than when they are
loaded. The decreased weight causes a vehicle’s wheels to have decreased traction on the
surface of the road.

Question 4

4. What is off-tracking?

Answer 4

› When a vehicle’s front wheels follow a different path than its rear wheels
When a vehicle goes around a corner, the rear wheels follow a different path than the front
wheels. This is known as off-tracking, or “cheating.”

Question 5

5. When backing a trailer, how should you turn the steering wheel?

Answer 5

› Turn the top of the steering wheel in the direction opposite of where you want the trailer
to go.
When backing with a trailer, turn the top of the steering wheel in the direction opposite of
where you want to go. Once the trailer begins turning, you should then switch the direction
of the steering wheel to follow the trailer.

Question 6

6. What does the trailer air supply control look like?

Answer 6

› It is an eight-sided red knob.
On newer vehicles, the trailer air supply control is an eight-sided red knob. It’s used to
control the tractor protection valve.

Question 7

7. Air pressure in the ____ air line is controlled by either the foot brake or trailer hand brake.

Answer 7

› Service
Air pressure in the service air line is controlled by either the foot brake or trailer hand brake.
The service air line is also known as the control line or signal line. This line is connected to
relay valves, which allow the trailer brakes to be applied more quickly than would otherwise
be possible.

Question 8

8. One function of the emergency air line is to:

Answer 8

› Control the emergency brakes.
The emergency air line (also known as the supply line) has two functions. The first is to
supply air to the trailer air tanks, and the second is to control the emergency brakes on
combination vehicles.

Question 9

9. Having ABS on only one axle:

Answer 9

› Will allow the driver additional control over their vehicle when braking.
Having an Anti-Lock Braking System (ABS) on only the trailer, or even on just one axle, will
still provide a driver with additional control over the trailer when braking.

Question 10

10. If a trailer begins to skid, the driver should:

Answer 10

› Release the brakes.
If your trailer starts to skid while you are braking, you should release the brakes and allow
them to begin to regain traction. Once its wheels have regained their grip on the road, the
trailer will begin to straighten out and follow the tractor.