Off-Tracking, Rollover Risk, Crash Avoidance Space, and Skid Correction

Off-Tracking on Corners

Off-tracking (or cut-in) is the phenomenon where the rear wheels of a long vehicle do not follow exactly in the path of the front wheels when cornering. The rear of the vehicle tracks a tighter radius than the front — it cuts toward the inside of the turn.

The longer the vehicle and the tighter the turn, the greater the off-tracking. On a heavy rigid vehicle this effect is significant because the wheelbase is long. If the driver positions the vehicle as a car would (hugging the inside of the lane), the rear wheels will cut inside and may mount a kerb, clip a cyclist, or cross into an adjacent lane.

Managing off-tracking

• Approach wide: Position the vehicle toward the outside of the turn on entry (while staying within your lane or safely using the opposite lane where legal and safe).
• Turn late: Begin the turn slightly later than a car would — this gives the rear wheels a path that clears the inside of the corner.
• Exit wide: Let the front of the vehicle move toward the outside of the turn on exit, then straighten.

This is often summarised as wide–late–wide and is the standard method for positioning a heavy vehicle through a corner. The driver must also be aware of the Do Not Overtake Turning Vehicle sign: vehicles over 7.5m displaying this sign may legally use more than one lane to turn, and other drivers must not overtake them.

Rollover Risk and High Centre of Gravity

Heavy rigid vehicles have a high centre of gravity compared to cars, especially when loaded. The higher the centre of gravity and the greater the load, the easier the vehicle is to roll over in a corner or during sudden steering inputs.

A loaded heavy vehicle can roll over at a lateral acceleration of approximately 0.35–0.4 g (about 3.5–4 m/s²). A passenger car can sustain 0.8–1.0 g before rolling. This means a heavy vehicle can roll over at speeds and cornering forces that feel unremarkable to a car driver.

Rollover prevention

• Reduce speed before cornering, not during it. All braking and gear selection should be complete before the turn. Braking mid-corner shifts weight forward and reduces traction on the rear (drive) axle, increasing the risk of a spin or rollover.
• Steer smoothly. Avoid sudden steering inputs. A quick steering correction that would be routine in a car can initiate a rollover in a loaded heavy vehicle because it generates a rapid lateral acceleration.
• Secure the load. An unsecured or shifting load changes the centre of gravity dynamically. A load that shifts to one side during cornering can trigger a rollover at a speed that would otherwise be safe.
• Be cautious on roundabouts and off-ramps. These are common rollover sites because drivers enter them at car-like speeds. Heavy vehicle advisory speed signs on curves are set for the rollover threshold of a loaded truck, not a car.

Crash Avoidance Space (CAS)

Crash Avoidance Space (CAS) is the core concept of Low Risk Driving (LRD). It means maintaining a buffer of time and space around the vehicle so that if a hazard appears, the driver has room to react and stop or steer.

The 12–15 second rule

A heavy vehicle driver should scan the road 12–15 seconds ahead at highway speeds. At 100 km/h, 12 seconds equates to roughly 330 metres. This gives the driver time to identify hazards — stopped traffic, debris, roadworks, merging vehicles — and begin reducing speed or planning a lane change well before reaching them.

For comparison, a car driver is typically taught to look 3–4 seconds ahead. A heavy vehicle needs far more lead time because of its longer stopping distance and air brake delay.

Following distance

Maintain at least 3 seconds of following distance behind the vehicle ahead in good conditions, increasing to 4–5 seconds in wet weather or when heavily loaded. At 100 km/h, 3 seconds = ~83 metres — close to the 60-metre minimum following distance rule for long vehicles in Victoria, but the time-based rule is safer because it scales with speed automatically.

Mirror checks

A heavy vehicle has significant blind spots — particularly down the passenger side ('off-side') where a car or motorcycle can disappear entirely. Drivers should check mirrors every 5–8 seconds and before any lane change, turn, or braking manoeuvre. The 'check your mirrors every 5 seconds' habit is a common test expectation.

Skid Types and Correction

Skids occur when tyres exceed their available grip — either from too much braking, too much acceleration, or too much steering for the conditions. Heavy vehicles are particularly prone because of their high mass, long wheelbase, and (for empty vehicles) low rear-axle traction.

Skid Type and Correction Table

The universal principle: ease off whatever caused the skid (brake or throttle), look where you want to go, and steer smoothly in that direction. Never brake hard in a skid — locking more wheels reduces control further.

Emergency Braking and Evasive Steering

When a hazard appears suddenly and there is no time for a normal stop, the driver must choose between two last-resort techniques:

Emergency (threshold) braking

If the path ahead is clear and the answer is to stop:

1. Apply firm, steady brake pressure — the maximum you can sustain without locking the wheels (threshold braking). If the vehicle has ABS, press the pedal hard and hold it; ABS will prevent lock-up.
2. Keep both hands on the wheel and steer straight. Do not pump the pedal on an ABS-equipped vehicle.
3. If wheels lock (non-ABS), release slightly and reapply — a rolling wheel can steer, a locked one cannot.
4. Use the auxiliary retarder (exhaust or engine brake) simultaneously to add deceleration without heating the service brakes.

Evasive steering

If stopping in time is not possible but a clear path exists to the side:

1. Look at where you want to go — not at the obstacle. The hands follow the eyes.
2. Steer smoothly and firmly around the hazard. A heavy vehicle can often steer around an obstacle in less distance than it can stop, particularly at higher speeds.
3. Counter-steer to bring the vehicle back onto your original path once past the hazard — do not over-correct.
4. If leaving the road is the only option, steer onto the shoulder or a clear area and brake gradually once off the sealed surface. Do not swerve into oncoming traffic.

The decision between braking and steering must be made in under a second. This is why maintaining 12–15 seconds of CAS is critical — it gives the driver time to choose the best option rather than reacting instinctively, which often results in a locked-wheel skid straight into the hazard.