Saudi Heavy Vehicle Theory key terms

The maximum total weight a vehicle is designed to carry safely, including the chassis, cab, body, fuel, cargo and occupants. It is set by the manufacturer and must never be exceeded on any road.

The weight of cargo, passengers and any added equipment that a vehicle can legally carry. It equals the gross vehicle weight rating minus the vehicle's own empty weight, called the kerb weight.

The maximum weight permitted on a single axle or axle group, stated by the manufacturer and enforced by road authorities. Overloading one axle damages roads, reduces steering control and increases tyre failure risk.

How a load's mass is spread across a vehicle's axles and along its length. Correct distribution keeps every axle within its limit, preserves steering grip and braking balance, and prevents trailer sway or jackknifing.

The methods and equipment, such as straps, chains, binders and tarpaulins, used to stop cargo shifting, sliding, tipping or falling from a vehicle during travel. Securement must be checked before departure and during the journey.

A manufacturer-approved anchor on the vehicle or load where straps or chains are attached. Attaching restraints to weak points such as body panels or brake lines can fail under load forces during braking or cornering.

The maximum force a strap, chain or tensioner is rated to hold safely. Each restraint must be rated for the load it secures, and the combined capacity must match the cargo weight and expected forces.

A braking system that uses compressed air to apply friction brakes at the wheels. It is standard on heavy trucks and buses because air is plentiful, stores energy for repeated stops and can power trailer brakes.

A cylinder that converts compressed air pressure into mechanical force to apply a wheel brake. A spring brake inside provides automatic parking and emergency braking if air pressure is lost.

A visual and audible alert that sounds when system air pressure falls below a safe level, typically around 60 psi. If it activates while driving, the driver must stop safely and find the fault.

Loss of braking power caused by overheating of brake drums, discs or linings after repeated or prolonged use. Drivers control it by gearing down and using engine braking on long descents rather than riding the brakes.

Using the resistance of a low gear and the engine's compression to slow a heavy vehicle without continuous wheel braking. It reduces heat build-up on long downhill grades and helps keep brake temperatures in a safe range.

The gap between your vehicle and the one ahead, measured in time rather than metres. Heavy vehicles need a longer gap than cars because of greater stopping distance, so a four-second or larger gap is often advised.

The total distance travelled from the moment a hazard is seen until the vehicle stops. It combines reaction distance and braking distance and grows sharply with speed and with vehicle weight.

Choosing and holding a speed that matches road conditions, visibility, load, traffic and the posted limit. For heavy vehicles the safe speed is often below the legal maximum, especially on bends, descents and in poor weather.

An area around a large vehicle that the driver cannot see in mirrors or directly. Heavy vehicles have large blind spots at the front, both sides and directly behind, so drivers must check carefully before turning or changing lanes.

The routine of scanning both side mirrors and any additional mirrors at regular intervals and before every manoeuvre. It reveals overtaking traffic, cyclists and pedestrians entering blind spots around a large vehicle.

A driving style that anticipates other road users' mistakes and keeps a safety margin. It means looking well ahead, planning escape routes, avoiding assumptions and adjusting speed before a hazard becomes an emergency.

The skill of noticing and predicting developing dangers, such as a pedestrian stepping out or a vehicle braking suddenly. It depends on scanning far ahead, reading road context and recognising patterns that signal risk.

The delay between realising a hazard and taking action, typically around one second for an alert driver. Fatigue, alcohol, distraction and illness lengthen it, so the vehicle travels further before braking begins.

A loss of control in which an articulated truck's tractor and trailer fold against each other. It often follows harsh braking on a slippery surface or loss of trailer grip, and it can block the road completely.

Side-to-side swinging of a trailer caused by poor weight distribution, crosswinds, sudden steering or excessive speed. The driver should ease off the accelerator and avoid harsh braking or sharp steering to regain control.

Physical and mental tiredness that slows reactions, impairs judgement and can cause micro-sleeps behind the wheel. Heavy vehicle drivers must plan rest breaks, respect driving-hour limits and stop when drowsiness appears.

The physical and mental condition a driver must be in to operate a heavy vehicle safely. It covers health, eyesight, medication effects, sleep, and freedom from alcohol or drugs that impair control.

The amount of alcohol in the bloodstream, expressed as a percentage or grams per litre. Any alcohol impairs judgement and reaction, and heavy vehicle drivers are usually held to a stricter limit than car drivers.

A systematic check of tyres, brakes, lights, fluids, couplings, load and safety equipment carried out before starting a journey. It catches defects early and is a legal duty for heavy vehicle operators in many jurisdictions.

A physical walk around the vehicle and trailer, looking and listening for damage, leaks, loose items and tyre problems. It complements the in-cab checks of gauges, warning lights and brake tests.

The condition of a vehicle being safe and legal to drive, with working brakes, lights, steering, tyres and bodywork. A vehicle that fails a required inspection must be repaired and re-certified before use.

A scheduled, official examination of a heavy vehicle's safety systems at intervals set by the licensing authority. Passing confirms the vehicle meets technical standards and is required to keep it registered for road use.

The height of the rubber pattern on a tyre, which channels water away and maintains grip. Heavy vehicles must meet minimum legal tread depths, and worn tyres increase stopping distance and blowout risk.

A class of driving licence that authorises operation of vehicles above a set weight or passenger capacity. Each category has age, medical, training and testing requirements, and driving outside your category is an offence.

The legal limits on continuous and total time spent driving, with required rest breaks, designed to prevent fatigue. Records may be kept in a logbook or digital tachograph and must be available for inspection.

Operating a vehicle above its gross weight rating, axle limit or registered payload. It reduces braking and steering performance, damages the road, voids insurance cover and attracts fines and possible licence penalties.

The duty to stop, exchange details, assist injured people and notify police or the insurer after a crash. Reports must be accurate and prompt, and failure to stop is a serious traffic offence.

Actions taken to protect people at a crash site, such as warning triangles, hazard lights, reflective clothing and moving to a safe location. The aim is to prevent secondary collisions while help is summoned.

Immediate care given to injured people before emergency services arrive, including checking for danger, calling for help and providing basic first aid. Untrained drivers should only act within their competence.

The grouping of signs into regulatory, warning and guide types. Regulatory signs impose duties or prohibitions, warning signs alert to hazards ahead, and guide signs give directions and information.

A regulatory sign showing the maximum legal speed for that road or zone. Limits may differ for heavy vehicles, and drivers must also reduce speed below the limit when conditions require it.

A regulatory sign that requires a specific action, such as stopping, turning or keeping to a lane. Ignoring a mandatory sign is a traffic offence and may carry fines or licence points.