DRTS Heavy-Vehicle Theory key terms

The maximum total weight a vehicle is permitted to carry, including the vehicle itself, fuel, passengers and cargo, as specified by the manufacturer or set by regulation.

The maximum permitted total weight of a towing vehicle together with all trailers it pulls, including all loads, fuel and occupants, as rated by the manufacturer or regulator.

The portion of a vehicle's total weight carried by a single axle or axle group, which must stay within regulated limits to protect roads and maintain stability.

The combination of lashings, chains, straps, gates, headboards and anchor points used to stop a load from shifting, sliding or falling off during travel and braking.

A tie-down device tightened before travel to hold a load firmly against the vehicle deck, using straps, chains or load binders to resist movement in all directions.

Movement of cargo from its secured position during braking, cornering or rough road travel, which can alter axle loads, destabilise the vehicle and cause rollover or loss of control.

The point at which a vehicle's combined weight is considered to act; raising or shifting it reduces stability and increases rollover risk, especially in heavy vehicles with high loads.

The level of lateral acceleration at which a vehicle tips over rather than sliding, determined by track width, centre of gravity height and suspension characteristics.

Sideways force experienced during cornering or evasive steering, measured relative to gravity; high values in tall heavy vehicles can exceed the rollover threshold.

A handling condition where the front wheels lose grip before the rear, causing the vehicle to continue straight instead of following the intended curve.

A handling condition where the rear wheels lose grip before the front, causing the rear of the vehicle to swing outward and the vehicle to turn more sharply than intended.

A dangerous condition in which an articulated vehicle's trailer swings sharply relative to the prime mover, often during braking on slippery surfaces or from loss of rear traction.

Side-to-side oscillation of a trailer or caravan at speed, which can worsen if the driver brakes abruptly or accelerates, and may lead to loss of control.

The primary braking system used during normal driving to slow and stop the vehicle, typically operated by the foot pedal and designed for repeated use.

A braking system that uses compressed air to apply force to brake chambers, common on heavy vehicles, requiring adequate air pressure and regular draining of moisture.

A component in an air brake system where compressed air acts on a diaphragm or piston to push the slack adjuster and apply the brakes.

A linkage device that transfers brake chamber pushrod force to the brake shoe or disc, and must be correctly adjusted to maintain effective braking and safe pushrod travel.

A temporary loss of braking power caused by overheating of brake linings or drums during prolonged or heavy braking, reducing friction and increasing stopping distance.

A retarding device that uses engine compression or exhaust restriction to slow the vehicle without using the service brakes, helping prevent brake fade on long descents.

An auxiliary slowing device, such as an engine brake, exhaust brake or transmission retarder, that reduces reliance on service brakes during long or steep descents.

A device that removes moisture from compressed air in an air brake system, preventing corrosion and ice formation that could impair brake performance.

A valve on an air tank that allows accumulated water and contaminants to be released, helping keep the air brake system clean and functioning correctly.

A mechanical or spring-applied braking system that holds a stationary vehicle in place, independent of the service brake and often required to secure a parked heavy vehicle.

A wedge placed against a wheel to prevent a parked vehicle from rolling, used as an additional safety measure when parking on a slope or during loading.

A routine inspection carried out before driving, covering tyres, lights, brakes, fluid levels, load security and couplings to confirm the vehicle is safe to operate.

A documented walk-around check of a heavy vehicle performed each day or before each shift, identifying safety defects and confirming roadworthiness before use.

A written record notifying the operator of any fault or damage found on a vehicle, so that repairs can be scheduled and the vehicle kept off the road if unsafe.

The condition of a vehicle being safe and legal to use on the road, with brakes, steering, tyres, lights and structure functioning correctly and meeting standards.

A state of physical or mental tiredness that impairs alertness, reaction time and judgement, increasing crash risk and managed through work and rest limits.

A record in which a heavy-vehicle driver logs work and rest periods, used to demonstrate compliance with fatigue management rules and to plan safe schedules.

A minimum period of non-work time that a driver must take between work periods to recover from fatigue and remain within regulated work limits.

A legal framework making parties such as employers, schedulers, loaders and drivers share responsibility for complying with heavy-vehicle safety and load laws.

The overarching legal obligation on parties in the transport chain to ensure, so far as reasonably practicable, the safety of transport activities and road users.

The steps a party must take to identify hazards, assess risks and implement controls, demonstrating reasonable efforts to comply with safety duties.

The ability to notice and anticipate developing road hazards early, such as merging traffic, pedestrians or changing conditions, allowing time for a safe response.

The gap maintained behind a vehicle ahead, which for heavy vehicles must allow for longer stopping distances and is often measured in seconds rather than metres.

The total distance travelled from the moment a hazard is seen until the vehicle comes to rest, including reaction distance and braking distance, longer for heavy vehicles.

An area around a heavy vehicle that the driver cannot see directly or through mirrors, where other road users may be hidden and at risk during turns or lane changes.

The actions taken after a crash to protect people and traffic, including warning devices, positioning the vehicle safely, and contacting emergency services without causing further harm.

A rapid, firm application of the brakes to avoid a collision, requiring the driver to maintain steering control and understand the vehicle's stopping capabilities.