Alberta Class 2 key terms

The maximum permitted pushrod travel for a brake chamber, measured with the brakes applied. Exceeding this limit means the brake cannot apply fully and the vehicle must be taken out of service until repaired.

A device in the air system that removes moisture from compressed air before it reaches the reservoirs, helping prevent corrosion and winter freeze-up of valves and lines.

A tank that stores compressed air for the braking system. Tanks must be drained of moisture and oil regularly, and the system must hold pressure without excessive leakage.

An aftermarket device that feeds alcohol vapour into the air system to prevent winter freezing. It can damage valves and seals and is not a substitute for a working air dryer.

The sealed unit where compressed air pushes a diaphragm and pushrod to apply the foundation brake. Its size and stroke determine braking force and the legal adjustment limit.

A valve that controls when the engine-driven compressor cuts in and out, keeping reservoir pressure within a set range, typically cutting out near 120 psi and cutting in again around 100 psi.

A petcock or lanyard-operated valve at the bottom of each air tank used to release accumulated water and oil. Tanks should be drained daily, and more often in humid or freezing weather.

A buzzer and light that activate when reservoir pressure drops to a dangerous level, warning the driver to stop safely before braking ability is lost.

A spring-applied, air-released brake that engages automatically when air pressure is lost, providing emergency stopping and holding the vehicle when parked.

The distance a brake chamber pushrod moves when the brake is applied. Measuring it during inspection shows whether the brake is within its legal adjustment limit.

The linkage that transfers pushrod force to the brake shoe and can be adjusted to remove excess play. It must keep pushrod travel within the legal limit.

A valve that seals the tractor's air supply when trailer lines separate or are disconnected, allowing the tractor to retain enough air to stop safely.

Couplers that connect the tractor's service and supply air lines to the trailer. They must be locked together and their seals inspected before every trip.

A required walk-around inspection completed by the driver before operating a commercial vehicle, covering brakes, tires, lights, coupling devices, load security and other safety items, with defects recorded.

A written record of any defect found during an inspection that affects safe operation. The vehicle must not be used until the defect is repaired and the record is dealt with as required.

The standards used by inspectors to decide that a commercial vehicle or driver must be removed from service immediately because a defect or condition makes operation unsafe.

A systematic check of a commercial vehicle before driving, including fluid levels, belts, tires, brakes, lights, mirrors, coupling and load security, done to catch problems before they cause a breakdown or crash.

The horseshoe-shaped coupling plate on a tractor that locks onto the trailer kingpin. It must be greased, properly latched and checked by tug test before driving.

The vertical pin under a semi-trailer that locks into the tractor's fifth wheel. Inspectors check it for wear, cracks and secure mounting.

A check after coupling in which the driver applies slight forward pull with the trailer brakes set to confirm the fifth wheel jaws are locked around the kingpin.

The qualification added to a licence that permits a driver to operate a vehicle equipped with air brakes, usually requiring a knowledge test and a practical air brake inspection.

A procedure in which the driver builds full pressure, shuts off the engine and watches the gauge to confirm the system loses no more than the permitted amount of air over a set time.

The maximum total weight a single vehicle is designed and permitted to carry, including its own weight, passengers, fuel and cargo, as set by the manufacturer.

The maximum total weight allowed for a tractor and its trailers together, including all cargo, fuel and equipment, as specified by the manufacturer.

The total load carried by all wheels on one axle. Each axle has a rated limit, and exceeding it overloads tires and brakes and may damage roads and bridges.

Two axles grouped closely together to share a load. Their combined weight is limited by regulation, and the load must be distributed so neither axle is overloaded.

Placing and securing cargo so weight is balanced over the axles and the centre of gravity stays low, preventing axle overload, poor steering and rollover risk.

The use of straps, chains, binders and tarps to keep cargo from shifting or falling. The number and strength of tiedowns must meet the standards for the load's weight and length.

A strap, chain, cable or web assembly used to anchor cargo to the vehicle. Working load limits must be marked and adequate for the weight and type of load carried.

The point where a load's weight is concentrated. A high or off-centre point of gravity makes a vehicle unstable in turns and increases the risk of rollover.

A crash in which a vehicle tips onto its side. High loads, fast cornering, sudden steering and unbalanced braking are common causes, and rollovers are especially deadly for heavy trucks.

The portion of a load that extends beyond the front or rear of the vehicle. It must be limited and marked as required, and must not obstruct lights, plates or visibility.

Loss of braking power when brakes overheat, common on long downgrades. Drivers prevent it by selecting a lower gear and using engine braking rather than continuous service braking.

A retarder that uses engine compression to slow the vehicle on long or steep grades, reducing reliance on the service brakes and helping prevent overheating and brake fade.

A gravel-filled emergency lane on a steep downgrade where a driver with failing brakes can steer to be stopped safely by deep loose material.

The safety margin around a vehicle that gives the driver time to react. It is maintained by following at a safe distance and avoiding travel in other drivers' blind spots.

The gap between your vehicle and the one ahead, measured in seconds. Large commercial vehicles need a longer gap to stop, and the gap should grow in poor weather or heavy loads.

An area around a vehicle that the driver cannot see in the mirrors. Large trucks have large blind spots, so drivers must check them carefully before lane changes and turns.

A quick glance over the shoulder to confirm no vehicle is hidden in the blind spot before changing lanes or merging, used together with mirror checks and signals.