PAGE 12
Hold the wheel tightly and turn sharply enough to
get right back on the road safely. Don't try to edge
gradually back on the road. If you do, your tires
might grab unexpectedly and you could lose
control.
When both front tires are on the paved surface,
counter-steer immediately. The two turns should
be made as a single "steer-counter-steer" move.
2.17.2 – How to Stop Quickly and Safely
If somebody suddenly pulls out in front of you, your
natural response is to hit the brakes. This is a good
response if there's enough distance to stop, and you
use the brakes correctly.
You should brake in a way that will keep your
vehicle in a straight line and allow you to turn if it
becomes necessary. You can use the "controlled
braking" method or the "stab braking" method.
Controlled Braking. With this method, you apply
the brakes as hard as you can without locking the
wheels. Keep steering wheel movements very small
while doing this. If you need to make a larger
steering adjustment or if the wheels lock, release
the brakes. Re-apply the brakes as soon as you
can.
Stab Braking. With this method, you apply your
brakes all the way and release brakes when wheels
lock up. As soon as the wheels start rolling, apply
the brakes fully again. (It can take up to one second
for the wheels to start rolling after you release the
brakes. If you re-apply the brakes before the wheels
start rolling, the vehicle won't straighten out.)
Don't Jam on the Brakes. Emergency braking
does not mean pushing down on the brake pedal as
hard as you can. That will only keep the wheels
locked up and cause a skid. If the wheels are
skidding, you cannot control the vehicle.
2.17.3 – Brake Failure
Brakes kept in good condition rarely fail. Most
hydraulic brake failures occur for one of two
reasons: (Air brakes are discussed in Section 5.)
Loss of hydraulic pressure.
Brake fade on long hills.
Loss of Hydraulic Pressure. When the system
won't build up pressure, the brake pedal will feel
spongy or go to the floor. Here are some things you
can do.
Downshift. Putting the vehicle into a lower gear will
help to slow the vehicle.
Pump the Brakes. Sometimes pumping the brake
pedal will generate enough hydraulic pressure to
stop the vehicle.
Use the Parking Brake. The parking or emergency
brake is separate from the hydraulic brake system.
Therefore, it can be used to slow the vehicle.
However, be sure to press the release button or pull
the release lever at the same time you use the
emergency brake so you can adjust the brake
pressure and keep the wheels from locking up.
Find an Escape Route. While slowing the vehicle,
look for an escape route--an open field, side-street,
or escape ramp. Turning uphill is a good way to slow
and stop the vehicle. Make sure the vehicle does
not start rolling backward after you stop. Put it in low
gear, apply the parking brake, and, if necessary, roll
back into some obstacle that will stop the vehicle.
Brake Failure on Downgrades. Going slow
enough and braking properly will almost always
prevent brake failure on long downgrades. Once the
brakes have failed, however, you are going to have
to look outside your vehicle for something to stop it.
Your best hope is an escape ramp. If there is one,
there'll be signs telling you about it. Use it. Ramps
are usually located a few miles from the top of the
downgrade. Every year, hundreds of drivers avoid
injury to themselves or damage to their vehicles by
using escape ramps. Some escape ramps use soft
gravel that resists the motion of the vehicle and
brings it to a stop. Others turn uphill, using the hill to
stop the vehicle and soft gravel to hold it in place.
Any driver who loses brakes going downhill should
use an escape ramp if it's available. If you don't use
it, your chances of having a serious crash may be
much greater.
If no escape ramp is available, take the least
hazardous escape route you can--such as an open
field or a side road that flattens out or turns uphill.
Make the move as soon as you know your brakes
don't work. The longer you wait, the faster the
vehicle will go, and the harder it will be to stop.
2.17.4 – Tire Failure
Recognize Tire Failure. Quickly knowing you have
a tire failure will let you have more time to react.
Having just a few extra seconds to remember what
it is you're supposed to do can help you. The major
signs of tire failure are:
Section 2 – Driving Safely Page 2-34
Version: July 2017
Commercial Driver’s License Manual – 2005 CDL Testing System
Sound. The loud "bang" of a blowout is an easily
recognized sign. Because it can take a few seconds
for your vehicle to react, you might think it was some
other vehicle. But any time you hear a tire blow,
you'd be safest to assume it is yours.
Vibration. If the vehicle thumps or vibrates heavily,
it may be a sign that one of the tires has gone flat.
With a rear tire, that may be the only sign you get.
Feel. If the steering feels "heavy," it is probably a
sign that one of the front tires has failed.
Sometimes, failure of a rear tire will cause the
vehicle to slide back and forth or "fishtail."
However, dual rear tires usually prevent this.
Respond to Tire Failure. When a tire fails, your
vehicle is in danger. You must immediately:
Hold the Steering Wheel Firmly. If a front tire
fails, it can twist the steering wheel out of your
hand. The only way to prevent this is to keep a firm
grip on the steering wheel with both hands at all
times.
Stay off the Brake. It's natural to want to brake in
an emergency. However, braking when a tire has
failed could cause loss of control. Unless you're
about to run into something, stay off the brake until
the vehicle has slowed down. Then brake very
gently, pull off the road, and stop.
Check the Tires. After you've come to a stop, get
out and check all the tires. Do this even if the
vehicle seems to be handling all right. If one of
your dual tires goes, the only way you may know it
is by getting out and looking at it.
2.18 – Antilock Braking Systems (ABS)
ABS is a computerized system that keeps your
wheels from locking up during hard brake
applications.
ABS is an addition to your normal brakes. It does
not decrease or increase your normal braking
capability. ABS only activates when wheels are
about to lock up.
ABS does not necessarily shorten your stopping
distance, but it does help you keep the vehicle under
control during hard braking.
2.18.1 – How Antilock Braking Systems Work
Sensors detect potential wheel lock up. An
electronic control unit (ECU) will then decrease
brake pressure to avoid wheel lockup.
Brake pressure is adjusted to provide the maximum
braking without danger of lockup.
ABS works far faster than the driver can respond to
potential wheel lockup. At all other times the brake
system will operate normally.
2.18.2 – Vehicles Required to Have Antilock
Braking Systems
The Department of Transportation requires that
ABS be on:
Truck tractors with air brakes built on or after
March 1, 1997.
Other air brake vehicles, (trucks, buses, trailers,
and converter dollies) built on or after March 1,
1998.
Hydraulically braked trucks and buses with a gross
vehicle weight rating of 10,000 lbs or more built on
or after March 1, 1999.
Many commercial vehicles built before these dates
have been voluntarily equipped with ABS.
2.18.3 – How to Know If Your Vehicle Is
Equipped with ABS
Tractors, trucks, and buses will have yellow ABS
malfunction lamps on the instrument panel.
Trailers will have yellow ABS malfunction lamps on
the left side, either on the front or rear corner.
Dollies manufactured on or after March 1, 1998, are
required to have a lamp on the left side.
As a system check on newer vehicles, the
malfunction lamp comes on at start-up for a bulb
check, and then goes out quickly. On older systems,
the lamp could stay on until you are driving over five
mph.
If the lamp stays on after the bulb check, or goes on
once you are under way, you may have lost ABS
control.
In the case of towed units manufactured before it
was required by the Department of Transportation,
it may be difficult to tell if the unit is equipped with
ABS. Look under the vehicle for the ECU and wheel
speed sensor wires coming from the back of the
brakes.
2.18.4 – How ABS Helps You
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.
Section 2 – Driving Safely Page 2-35
Version: July 2017
Commercial Driver’s License Manual – 2005 CDL Testing System
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.
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, the 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.
2.18.7 – Braking If ABS Is Not Working
Without ABS you still have normal brake functions.
Drive and brake as you always have.
Vehicles with ABS have yellow malfunction lamps to
tell you if something isn’t working.
As a system check on newer vehicles, the
malfunction lamp comes on at start-up for a bulb
check and then goes out quickly. On older systems,
the lamp could stay on until you are driving over five
mph.
If the lamp stays on after the bulb check, or goes on
once you are under way, you may have lost ABS
control on one or more wheels.
Remember, if your ABS malfunctions, you still have
regular brakes. Drive normally, but get the system
serviced soon.
2.18.8 – Safety Reminders
ABS won’t allow you to drive faster, follow more
closely, or drive less carefully.
ABS won’t prevent power or turning skids–ABS
should prevent brake-induced skids or jackknifes,
but not those caused by spinning the drive wheels
or going too fast in a turn.
ABS won’t necessarily shorten stopping
distance. ABS will help maintain vehicle control,
but not always shorten stopping distance.
ABS won’t increase or decrease ultimate
stopping power–ABS is an “add-on” to your
normal brakes, not a replacement for them.
ABS won’t change the way you normally brake.
Under normal brake conditions, your vehicle will
stop as it always stopped. ABS only comes into
play when a wheel would normally have locked up
because of over braking.
ABS won’t compensate for bad brakes or poor
brake maintenance.
Remember: The best vehicle safety feature is still
a safe driver.
Remember: Drive so you never need to use your
ABS.
Remember: If you need it, ABS could help to
prevent a serious crash.
2.19 – Skid Control and Recovery
A skid happens whenever the tires lose their grip on
the road. This is caused in one of four ways:
Over-braking. Braking too hard and locking up the
wheels. Skids also can occur when using the speed
retarder when the road is slippery.
Over-steering. Turning the wheels more sharply
than the vehicle can turn.
Over-acceleration. Supplying too much power to
the drive wheels, causing them to spin.
Driving Too Fast. Most serious skids result from
driving too fast for road conditions. Drivers who
adjust their driving to conditions don't over-
accelerate and don't have to over-brake or over-
steer from too much speed.
Section 2 – Driving Safely Page 2-36
Version: July 2017
Commercial Driver’s License Manual – 2005 CDL Testing System
2.19.1 – Drive-wheel Skids
By far the most common skid is one in which the
rear wheels lose traction through excessive braking
or acceleration. Skids caused by acceleration
usually happen on ice or snow. Taking your foot off
the accelerator can easily stop them. (If it is very
slippery, push the clutch in. Otherwise, the engine
can keep the wheels from rolling freely and
regaining traction.)
Rear wheel braking skids occur when the rear drive
wheels lock. Because locked wheels have less
traction than rolling wheels, the rear wheels usually
slide sideways in an attempt to "catch up" with the
front wheels. In a bus or straight truck, the vehicle
will slide sideways in a "spin out." With vehicles
towing trailers, a drive-wheel skid can let the trailer
push the towing vehicle sideways, causing a
sudden jackknife. See Figure 2.19.
2.19.2 – Correcting a Drive-wheel Braking Skid
Do the following to correct a drive-wheel braking
skid.
Stop Braking. This will let the rear wheels roll
again, and keep the rear wheels from sliding.
Counter-steer. As a vehicle turns back on course,
it has a tendency to keep on turning. Unless you turn
the steering wheel quickly the other way, you may
find yourself skidding in the opposite direction.
Learning to stay off the brake, turn the steering
wheel quickly, push in the clutch, and counter-steer
in a skid takes a lot of practice. The best place to
get this practice is on a large driving range or "skid
pad."
2.19.3 – Front-wheel Skids
Driving too fast for conditions causes most front-
wheel skids. Other causes include lack of tread on
the front tires and cargo loaded so not enough
weight is on the front axle. In a front-wheel skid, the
front end tends to go in a straight line regardless of
how much you turn the steering wheel. On a very
slippery surface, you may not be able to steer
around a curve or turn.
When a front-wheel skid occurs, the only way to
stop the skid is to let the vehicle slow down. Stop
turning and/or braking so hard. Slow down as
quickly as possible without skidding.
Figure 2.19
Subsections 2.17, 2.18, and 2.19
Test Your Knowledge
1. Stopping is not always the safest thing to do
in an emergency. True or False?
2. What are some advantages of going right
instead of left around an obstacle?
3. What is an "escape ramp?"
4. If a tire blows out, you should put the brakes
on hard to stop quickly. True or False?
5. How do you know if your vehicle has antilock
brakes?
6. What is the proper braking technique when
driving a vehicle with antilock brakes?
7. How do antilock brakes help you?
These questions may be on the test. If you can’t
answer them all, re-read subsections 2.17, 2.18,
and 2.19.
Section 2 – Driving Safely Page 2-37
Version: July 2017
Commercial Driver’s License Manual – 2005 CDL Testing System
PAGE 12