CDL: Emergency Braking, Brake Failure, and Tire Failure

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Driving Emergencies: Braking Hard, Brake Failure, and Tire Failure

When something goes wrong on the road, the seconds right after are what determine whether the situation turns into a close call or a crash. This article covers three emergency scenarios every commercial driver needs to know how to handle: stopping quickly and safely, responding to a loss of hydraulic brakes, and reacting to a tire that suddenly fails.

Emergency Braking: How to Stop Quickly and Safely

When another vehicle suddenly pulls out in front of you, the natural instinct is to hit the brakes hard. That instinct is the right one, as long as there's enough distance to stop and the brakes are applied correctly.

The goal in an emergency stop is to brake in a way that keeps the vehicle traveling in a straight line while still leaving you the option to steer if needed. There are two accepted methods for doing this: controlled braking and stab braking.

Controlled Braking

With this method, you apply the brakes as firmly as possible without locking the wheels, while keeping any steering adjustments small. If you need to make a bigger steering correction, or if the wheels do lock up, release the brakes and then reapply them as quickly as you can.

Stab Braking

• Apply the brakes fully.
• Release the brakes as soon as the wheels lock up.
• As soon as the wheels start rolling again, apply the brakes fully once more.

Timing matters here — it can take up to a full second for the wheels to start rolling again after you release the brakes. If you reapply the brakes before the wheels have started rolling, the vehicle won't straighten back out.

Brake Failure

Brakes that are properly maintained rarely fail outright. When hydraulic brakes do fail, it's almost always for one of two reasons: a loss of hydraulic pressure, or brake fade caused by long hills. (Air brake systems are covered separately in the manual.)

Loss of Hydraulic Pressure

When the hydraulic system can't build pressure, the brake pedal will feel spongy, or it may go all the way to the floor. If this happens, there are several things you can try:

• Downshift. Dropping into a lower gear helps slow the vehicle using engine braking.
• Pump the brakes. Repeatedly pumping the pedal can sometimes generate enough hydraulic pressure to bring the vehicle to a stop.
• Use the parking brake. Because the parking or emergency brake operates independently of the hydraulic system, it can still be used to slow the vehicle. Just be sure to hold the release button or lever while applying it, so you can modulate the pressure and avoid locking the wheels.
• Look for an escape route. While slowing down, scan for an open field, a side street, or an escape ramp. Turning uphill is often an effective way to slow and stop. Once stopped, make sure the vehicle doesn't start rolling backward — shift into low gear, set the parking brake, and if necessary, roll back into an obstacle that will hold the vehicle in place.

Brake Failure on Downgrades

Driving at an appropriate speed and braking correctly will almost always prevent brake failure on a long downgrade. But once the brakes are gone, your only remaining option is to find something outside the vehicle that can bring it to a stop.

An escape ramp is your best chance if one is available — signs will typically indicate where they're located, usually a few miles before the top of the downgrade. Many drivers avoid injury and vehicle damage every year simply by using these ramps when their brakes fail. If there's no escape ramp nearby, take the safest alternative route you can find, such as an open field or a side road that levels out or climbs. Act as soon as you realize the brakes aren't working — the longer you wait, the faster the vehicle will be moving, and the harder it becomes to stop.

Tire Failure

Recognizing Tire Failure

Knowing right away that a tire has failed gives you extra time to respond correctly. The main warning signs include:

• Sound. A loud bang is the classic sign of a blowout. Because it takes a moment for the vehicle to react, it's easy to assume the noise came from another vehicle — but it's safest to assume any tire blowout you hear is your own.
• Vibration. A heavy thump or vibration can indicate a flat tire. With a rear tire, this vibration may be the only clue you get.
• Feel. Steering that suddenly feels heavy usually points to a failed front tire. A failed rear tire can sometimes cause the vehicle to fishtail, though dual rear tires typically prevent this from happening.

Responding to Tire Failure

Once a tire fails, the vehicle is in a vulnerable position, and you need to act immediately:

• Hold the wheel firmly. A failed front tire can wrench the steering wheel out of your grip. Keeping a firm, two-handed hold on the wheel at all times is the only reliable way to prevent this.
• Stay off the brake. Braking right after a tire failure can cause you to lose control. Unless you're about to hit something, avoid the brake until the vehicle has slowed down naturally, then brake gently and pull off the road.
• Check the tires once stopped. Get out and inspect every tire, even if the vehicle seemed to be handling fine. If one of a pair of dual tires has failed, sometimes the only way to know is to look.

Emergencies on the road rarely give much warning, which is exactly why these procedures are worth knowing before you need them. Practicing controlled or stab braking, understanding your options if the hydraulic brakes fail, and knowing how to hold the wheel and stay off the brake after a tire blows all give you a better chance of keeping the vehicle under control when it matters most.