A combination has 16 brakes and two are out of adjustment. What happens?

The others overwork and the stop is longer

The vehicle stops sooner on that side

How do you make an emergency stop in a vehicle with ABS?

Firm, steady pressure; do not pump

Pump the pedal quickly to stop the wheels locking

BC Class 1–4: Heavy vehicle braking

How brakes turn motion into heat, stopping time and following distance, speed and weight effects, brake fade, retarders, downgrades, water, runaway lanes and ABS.

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Heavy vehicle braking · Question 1Score 0/0

What should you do after driving through deep water?

Tip: press 1–4 to answer and Enter for the next question.

Study reference: Driving Commercial Vehicles (ICBC, 2024 edition), Ch. 2 Heavy vehicle braking — Stopping distance, Brake heat, Retarders, Downgrades, Anti-lock braking systems

All 15 questions in this test

Every question and its answer choices. The correct answers and explanations appear when you take the test above.

What should you do after driving through deep water?
1. Hold light brake pressure briefly
2. Pump the brakes hard several times to dry them
3. Stop and wait for the brakes to dry
4. Nothing; air brakes are not affected
A combination has 16 brakes and two are out of adjustment. What happens?
1. The ABS balances it out fully
2. The others overwork and the stop is longer
3. Nothing, 14 brakes are enough
4. The vehicle stops sooner on that side
How do you make an emergency stop in a vehicle with ABS?
1. Apply the trailer brakes only
2. Pump the pedal quickly to stop the wheels locking
3. Lock the wheels, then release
4. Firm, steady pressure; do not pump
What is the maximum fine for operating a vehicle whose brakes are not properly adjusted?
1. $2,000
2. $10,000
3. $500
4. $200
If you double both speed and weight, how much more stopping power is needed?
1. Six times
2. Twice
3. Eight times
4. Four times
How should you choose your gear for going down a hill?
1. Neutral, using only the brakes
2. A lower gear than you used to climb it
3. The same gear you used to climb it
4. A higher gear to save fuel
What is the most common air brake defect found in commercial vehicle inspections?
1. Frozen air dryers
2. Leaking glad hand seals
3. Brakes out of adjustment
4. Low compressor oil
Your speed creeps above your chosen speed on a downgrade. What does the guide advise?
1. Ride the brakes lightly to the bottom
2. Use the splitter to change gear
3. Brake to drop 10–15 km/h, then downshift
4. Shift up to ease the engine
Which vehicles must have ABS in Canada?
1. All trucks and buses built since 1990, whatever their weight
2. Only tractors that pull double trailers
3. Trucks and buses over 4,560 kg built since April 2000
4. Only school buses and coaches
What temperature should brake components not exceed?
1. About 500 °C
2. About 250 °C
3. About 80 °C
4. About 120 °C
At highway speed, what is the minimum following time for a bus or heavy truck?
1. Ten seconds
2. Two seconds
3. Three seconds
4. Five seconds
When does an engine retarder work best?
1. At low engine r.p.m. and high road speed
2. Only when the clutch is pressed
3. Only on slippery roads
4. At higher engine r.p.m. and lower road speed
About how long is air brake lag?
1. One-tenth of a second
2. Two seconds
3. Four-tenths of a second
4. Three-quarters of a second
What do brakes turn the energy of a moving vehicle into?
1. Air pressure
2. Heat
3. Sound
4. Electricity
What is brake fade?
1. Overheated brakes losing power
2. Brake linings slowly wearing thin with age
3. Brakes freezing in cold weather
4. Air leaking slowly from the tanks

Heavy vehicle braking: key rules to remember

Our summary of what the official handbook says on this topic, in our own words. Read it before or after the practice questions above, then check the original chapter. Read the official chapter ↗

Starting and stopping, power to move and power to stop (p. 17–18)

An engine turns heat energy into motion; brakes do the opposite and turn the energy of motion back into heat through friction between linings/pads and drums/rotors.
Brake heat is mostly given off to the air through the brake drums or rotors.
The final factor in stopping (and in moving) is the grip of the tires on the road; bald or defective tires reduce braking.
A loaded heavy tractor-trailer can weigh up to 63,500 kg.
A heavy combination may need over one kilometre and over one minute to reach 100 km/h, but may have to stop from 100 km/h in about seven seconds.
Stopping that quickly needs about nine times the accelerating force, roughly 4,000 hp.
On a combination with eight equally loaded axles and 16 brakes, each brake does about 1/16 of the work; if one or two are out of adjustment the others overwork and stopping distance grows.
Unequally loaded axles let lightly loaded wheels skid, which also lengthens stopping distance.

Stopping distance and stopping time (p. 19)

Total stopping time = perception time + reaction time + brake lag time + braking time.
Average perception time (see-think) is about 3/4 of a second and reaction time (do) another 3/4 of a second.
Air brakes have a brake lag of about 4/10 of a second between pressing the pedal and the brakes working; a car's hydraulic brakes act almost instantly.
Cars and light trucks use a two-second following rule; buses, trucks and other heavy vehicles should never be less than five seconds behind at highway speed.
Stopping takes even longer when brakes are out of adjustment or the vehicle is going downhill.
The most common air brake defect found in commercial vehicle inspections is brakes out of adjustment.

Speed and weight facts (p. 20–21)

Doubling speed needs four times the stopping power.
Doubling weight needs twice the stopping power.
Doubling both speed and weight needs eight times the stopping power.
A loaded truck of about 25,000 kg is over 25 times heavier than a 1,000 kg compact car.
Going downhill lengthens stopping distance; going uphill shortens it, because of gravity.
Driving without due care and attention and unsafe speed are the top two factors assigned to commercial drivers in police-reported casualty crashes.

How much heat can brakes handle? (p. 21)

In normal stops brake parts reach about 120 °C; they can handle up to about 250 °C under hard braking and should not exceed it.
As drums heat up they expand away from the linings.
Brake fade is overheated brakes losing effectiveness, so the vehicle takes longer to stop or may not stop.
Too much heat can cause brake fade, damage or failure, and brake parts or tires can catch fire.

Retarders (p. 22)

Retarders give auxiliary slowing, for example on long downgrades, to save the service brakes for emergencies.
The four main types are engine, exhaust, hydraulic driveline and electric driveline retarders.
An engine retarder works best at higher engine r.p.m. and lower road speed, so pick the gear before starting down the hill.
On slippery roads some retarders can lock the drive wheels, stall the engine and cause loss of control or a jackknife.
Obey municipal signs that restrict engine brake use.

Braking, icy roads and downgrades (p. 23–25)

Ease pedal pressure just before the vehicle stops to avoid jerking.
On ice use very light brake pressure; a slowly turning wheel stops better than a locked, skidding one.
Use designated chain-up areas; do not deflate tires to fit chains; check chain tightness at the first safe opportunity and slow down with chains on.
Operating with brakes not correctly adjusted or not performing adequately can bring a fine of up to $2,000.
Almost all brake failures and runaway crashes on hills are caused by poor speed control that overdrives the brakes' ability to handle heat.
Go down a hill in a lower gear than you used to climb it; never upshift on a downgrade unless a retarder or engine compression can control speed.
On highway downgrades obey truck advisory speeds, use four-way flashers, stay in the far right lane where possible.
With the right low gear and the retarder, you should be able to descend without the service brakes.
If speed rises above your chosen speed: brake hard enough to drop 10 to 15 km/h, then downshift to a lower main gear (do not use the splitter on a downhill); repeat if needed.
Keep the vehicle in gear all the way down the hill.
A grade sign showing 18 per cent indicates a very steep hill; the higher the percentage the steeper the grade.
Always obey regulatory stop-and-check-brakes signs.

Water, runaway lanes and combination braking (p. 25)

Before driving through water, cover the brake and drag the brakes lightly while in the water to keep water out; slow down first.
After water or very wet conditions, hold light brake pressure for a short distance to dry the brakes.
Runaway lanes are only for slowing or stopping a vehicle whose brakes have failed on a downgrade.
With air brakes, pressing the pedal applies all brakes at the same time and same pressure.
Braking too hard, or applying only the trailer brakes on slippery roads, can lock wheels and cause a skid or jackknife.
An empty vehicle without ABS can bounce and lock its wheels, lengthening stopping distance.
It is hard to stop a multiple-trailer combination in a straight line in an emergency.

Anti-lock braking systems and traction control (p. 25–27)

ABS is mandatory in Canada on trucks and buses over 4,560 kg built since April 1, 2000, and on all commercial trailers with air brakes.
ABS does not let you drive faster or stop sooner; on gravel stopping with ABS may be longer.
ABS prevents wheel lock-up so you can brake hard and keep steering control, and may help prevent a jackknife.
Emergency stop with ABS: firm, hard, continuous pedal pressure; do not pump; noise, pedal movement and shudder are normal.
If not every unit in a combination has ABS, brake as if the combination had no ABS.
A full jackknife is when tractor and trailer form an angle of 90 degrees or less; it can happen even at very low speeds and often comes from poor braking, including misuse of retarders.
Automatic traction control (ATC) is an optional add-on to ABS that uses the ABS wheel sensors to detect a spinning drive wheel, brakes that wheel and can cut engine power.
Vehicles with ATC usually have a dash lamp that lights when wheel spin occurs.

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