4.4 Hills, Curves, Weather and Animals

Plan the entire hill

A posted speed limit is a maximum under the applicable rules, not proof that the speed is safe for a loaded vehicle on every grade. The descent plan should consider gradient, length, load, brake condition, weather, bends and available stopping areas. Choose the speed and gear before gravity begins accelerating the vehicle, while there is still time to make a controlled decision.

A suitable lower gear permits engine or auxiliary braking to help control speed. The correct gear depends on the vehicle, transmission, load and hill. Do not memorise a universal instruction such as 'always use second gear' or assume that the gear used uphill must be adequate downhill. Manufacturer limits on engine speed and the retarding system still apply.

Low-gear signs and braking

The current road rule for a TRUCKS AND BUSES MUST USE LOW GEAR sign requires a gear low enough to control speed without using the primary brake. The sign does not itself require the vehicle to stop at the top. A driver may need a safe stop for checks or planning in the actual situation, but that decision should not be presented as an invented universal sign rule.

Auxiliary brakes include engine, exhaust and other retarders. They reduce the demand on service brakes but generally do not provide the complete final stop. Their effect can depend on engine speed and system design. A driveline retarder may act through the drive wheels, so on a slippery surface it can demand more traction than those tyres can provide. Follow the vehicle’s instructions and reduce or avoid the retarder setting when grip is inadequate.

Repeated or prolonged service braking converts the vehicle’s energy into heat. If the brakes cannot dissipate that heat, their effectiveness can fall. The precise temperature and performance depend on the system; there is no single fade temperature for every truck. The practical control is to enter slowly enough that the selected gear and auxiliary system can manage the hill without overworking the service brakes.

Transmission decisions

Select a suitable gear or approved downhill mode before the descent. An automatic or automated transmission does not make the task self-managing; learn its mode selection and gear-holding behaviour. Some systems can shift in ways requiring planning. Avoid neutral coasting, which removes useful engine control and makes re-engagement more difficult. Do not force a gear that would overspeed the engine.

If a gear is missed or the selected ratio is inadequate, follow the vehicle’s procedure and use the remaining control to find a safe stop. Do not turn a general study guide into an unqualified emergency instruction to engage an unknown gear at any speed. The driver’s training and the actual manufacturer’s limits govern.

Climbing hills

Shift down early before the engine begins lugging—shuddering or excessive vibration from operating at an unsuitable low speed under load. Use the manufacturer’s torque range rather than waiting until the vehicle loses useful momentum. A steep climb can require moving down more than one ratio through the trained procedure. Keep a safe gap, watch following traffic and avoid forcing an unsuitable gear. If movement stops, secure the vehicle through its proper hill-start procedure and confirm a safe restart.

Curves and roundabouts

Slow before entering a curve where possible, allowing braking and gear selection in a stable approach. A high centre of gravity, shifting liquid or off-centre cargo reduces the margin for cornering. The cab may feel comfortable while the trailer is approaching an unsafe lateral demand. Advisory curve speeds are a warning to assess the situation; a loaded heavy vehicle may require a lower speed.

Look through the curve, keep a safe path and steer smoothly. Avoid harsh acceleration, braking or lane changes within it. Do not cut across the centreline because the truck is long. If the available road width cannot accommodate the vehicle safely, route selection or traffic management must solve the problem before the turn.

Weather and visibility

Rain reduces grip and can conceal potholes or standing water. Frost and ice can be difficult to see, particularly on shaded roads and bridges. Fog, smoke and heavy spray shorten visible stopping distance. Reduce speed and increase the gap before the hazard becomes critical. Use the appropriate lights, keep windows clear and do not use high beam when it worsens glare in fog or for other road users.

Strong wind can affect high-sided and lightly loaded vehicles. Watch exposed bridges and gaps in shelter, maintain a firm but smooth steering input and stop safely if conditions exceed control. Do not park beneath unstable branches or where the vehicle obstructs traffic. Do not enter floodwater when depth, current or road condition is uncertain; find a safe alternative.

Animals and other sudden hazards

Scan road edges, especially around dusk, dawn and livestock movements. Slow where animals may enter the road. If one appears, brake under control and maintain a safe path rather than swerve blindly. Watch for others following it. After a collision or near miss, stop only where safe and follow reporting and assistance duties.

Animals carried in or led from a vehicle

The handbook also covers animals being transported, beyond animals encountered on the road. House or seat them in an appropriate area so they cannot interfere with steering, pedals or observation. Never drive with an animal in the driver’s lap. A driver or passenger must not lead an animal, including by tethering, while the vehicle is moving. A dog on a lead beside a slowly moving truck is still within that prohibition; park and use a safe separate handling arrangement.

Key decisions

Set the descent up early, keep demands within grip and braking capability, and adapt speed to the road that can actually be seen and controlled.

Official sources

Road Rules 2019, rule 108; official handbook, safe driving and auxiliary brakes. Sources checked 10 October 2026.