When you brake hard on slippery surfaces in a vehicle without ABS, your wheels may lock up. When your steering wheels lock up, you lose steering control. When your other wheels lock up, you may skid, jackknife, or even spin the vehicle.
ABS helps you avoid wheel lock-up and maintain control. You may or may not stop faster with ABS, but you should be able to steer around an obstacle while braking and avoid skids caused by over braking.

2.18.5 – ABS on the Tractor Only or Only on the Trailer

Having ABS on only the tractor, only the trailer, or even on only one axle still gives you more control over the vehicle during braking. Brake normally.
When only the tractor has ABS, you should be able to maintain steering control and there is less chance of jackknifing. But keep your eye on the trailer and let up on the brakes (if you can safely do so) if it begins to swing out.
When only the trailer has ABS, the trailer is less likely to swing out, but if you lose steering control or start a tractor jackknife, let up on the brakes (if you can safely do so) until you regain control.

2.18.6 – Braking with ABS

When you drive a vehicle with ABS, you should brake as you always have. In other words:

Use only the braking force necessary to stop safely and stay in control.
Brake the same way, regardless of whether you have ABS on the bus, tractor, trailer, or both.
As you slow down, monitor your tractor and trailer and back off the brakes (if it is safe to do so) to stay in control.
There is only one exception to this procedure. If you drive a straight truck or combination with working ABS on all axles, in an emergency stop, you can fully apply the brakes.

Multiple-Choice Questions:

Question #161 (1 of 4)

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What is the primary reason ABS was invented?

To help you avoid wheel lock-up during hard braking and maintain control
To apply enough braking force to lock up the tires when needed
To add additional braking force to the system during emergency stops
To lock the steering in a straight line during hard braking, preventing a possible jackknife

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ABS helps you avoid wheel lock-up and maintain control. You may or may not be able to stop faster with ABS, but you should be able to steer around an obstacle while braking and avoid skids caused by over braking.

Question #162 (2 of 4)

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Which of the following is true about having ABS on only the tractor, only on the trailer, or only on one axle?

Having ABS on only the tractor, only the trailer, or even on only one axle does almost no good whatsoever. You should brake as if you do not have ABS at all.
Having ABS on only the tractor, only the trailer, or even on only one axle gives you less control over the vehicle during braking than without any ABS at all. Brake more cautiously than without ABS.
Having ABS on only the tractor, only the trailer, or even on only one axle still gives you more control over the vehicle during braking, but greatly increases your chances of jackknifing on slick roads if you don't use stab braking
Having ABS on only the tractor, only the trailer, or even on only one axle still gives you more control over the vehicle during braking. Brake normally.

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Having ABS on only the tractor, only the trailer, or even on only one axle still gives you more control over the vehicle during braking. Brake normally.

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Question #160 (3 of 4)

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Which of the following are true about ABS systems?

ABS will sometimes cause wheel lock-up under hard braking but will help you maintain control, even during a jackknife. You may or may not be able to stop faster with ABS, but you can put more air pressure into the braking system to help you lock up the tires.
ABS helps you avoid wheel lock-up but can compromise your ability to control the vehicle. You will certainly stop faster with ABS, but only in a straight line. You will not be able to steer while under heavy braking.
ABS helps you avoid wheel lock-up and maintain control. You may or may not be able to stop faster with ABS, but you should be able to steer around an obstacle while braking and avoid skids caused by over braking.
ABS will help the wheels lock up under hard braking, allowing you to stop faster with ABS, but you will not be able to steer around an obstacle while braking or avoid skids caused by over braking.

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Question #163 (4 of 4)

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When you drive a vehicle with ABS, you should brake as you always have. There is only one exception to this procedure:

If you drive a straight truck or combination with working ABS on all axles, in an emergency stop, you can fully apply the brakes.
If you drive a straight truck or combination with working ABS on all axles, in an emergency stop, you can only apply the brakes fully on slick roads. Doing so on dry roads will lock up the tires.
If you drive a straight truck or combination vehicle with working ABS on the trailer only, you must only use controlled braking and never try stab braking
If you drive a combination vehicle with working ABS on the tractor only, make sure you use stab braking only

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There is only one exception to this procedure. If you drive a straight truck or combination with working ABS on all axles, in an emergency stop, you can fully apply the brakes.

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