Driving Emergencies, ABS & Skid Control
2.17 – Driving Emergencies
Traffic emergencies occur when two vehicles are about to collide. Vehicle emergencies occur when tires, brakes, or other critical parts fail. Following the safety practices in this manual can help prevent emergencies. But if an emergency does happen, your chances of avoiding a crash depend upon how well you take action. Actions you can take are discussed below.
2.17.1 – Steering to Avoid a Crash
Stopping is not always the safest thing to do in an emergency. When you don’t have enough room to stop, you may have to steer away from what’s ahead. Remember, you can almost always turn to miss an obstacle more quickly than you can stop. (However, top-heavy vehicles and tractors with multiple trailers may flip over.)
Keep Both Hands on the Steering Wheel. In order to turn quickly, you must have a firm grip on the steering wheel with both hands. The best way to have both hands on the wheel, if there is an emergency, is to keep them there all the time.
How to Turn Quickly and Safely. A quick turn can be made safely, if it’s done the right way. Here are some points that safe drivers use:
- Do not apply the brake while you are turning. It’s very easy to lock your wheels while turning. If that happens, you may skid out of control.
- Do not turn any more than needed to clear whatever is in your way. The more sharply you turn, the greater the chances of a skid or rollover.
- Be prepared to “countersteer,” that is, to turn the wheel back in the other direction, once you’ve passed whatever was in your path. Unless you are prepared to countersteer, you won’t be able to do it quickly enough. You should think of emergency steering and countersteering as two parts of one driving action.
Where to Steer. If an oncoming driver has drifted into your lane, a move to your right is best. If that driver realizes what has happened, the natural response will be to return to his or her own lane.
If something is blocking your path, the best direction to steer will depend on the situation.
- If you have been using your mirrors, you’ll know which lane is empty and can be safely used.
- If the shoulder is clear, going right may be best. No one is likely to be driving on the shoulder but someone may be passing you on the left. You will know if you have been using your mirrors.
- If you are blocked on both sides, a move to the right may be best. At least you won’t force anyone into an opposing traffic lane and a possible head-on collision.
Leaving the Road. In some emergencies, you may have to drive off the road. It may be less risky than facing a collision with another vehicle.
Most shoulders are strong enough to support the weight of a large vehicle and, therefore, offer an available escape route. Here are some guidelines, if you do leave the road.
Avoid Braking. If possible, avoid using the brakes until your speed has dropped to about 20 mph. Then brake very gently to avoid skidding on a loose surface.
Keep One Set of Wheels on the Pavement, if Possible. This helps to maintain control.
Stay on the Shoulder. If the shoulder is clear, stay on it until your vehicle has come to a stop. Signal and check your mirrors before pulling back onto the road.
Returning to the Road. If you are forced to return to the road before you can stop, use the following procedure:
- 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, countersteer immediately. The two turns should be made as a single “steer-countersteer” 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.
- Apply your brakes all the way.
- 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:
- 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.
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 & 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.
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.
- Countersteer. 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 countersteer 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
Test Your Knowledge
- Stopping is not always the safest thing to do in an emergency. True or False?
- What are some advantages of going right instead of left around an obstacle?
- What is an “escape ramp?”
- If a tire blows out, you should put the brakes on hard to stop quickly. True or False?
- How do you know if your vehicle has antilock brakes?
- What is the proper braking technique when driving a vehicle with antilock brakes?
- 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