Load Shift on a Roundabout

High centre of gravity: With 2.8 m of stacked, unwrapped pallets, the load's centre of gravity is high. In a curve, lateral acceleration acts at the centre of gravity, producing a roll moment that increases with height. The vehicle leans more than a low-load combination would at the same speed.

Delayed trailer response: A B-double has a long combination and articulation points. When the prime mover enters the curve, the lead trailer follows later, and the rear trailer later again. Each unit's lateral force builds at a different time, so the lead trailer's lean arrives after the prime mover's - the "delayed, heavier lean" you felt. This phase lag can produce rearward amplification, where the rear unit's lateral response is larger than the prime mover's, increasing rollover risk.

Light steering: As the vehicle rolls, weight transfers to the outside wheels. The front axle can unload, reducing tyre normal force and therefore steering grip, so the steering feels light and less responsive. Simultaneously, the load shifting outward moves the centre of gravity further outboard, increasing the roll moment - a positive feedback loop.

Key point: 45 km/h is not automatically safe. Rollover is governed by centre-of-gravity height, track width, and lateral acceleration, not by the posted limit. A high-CG B-double can roll at well below the sign speed.

Immediate actions:

1. Do not brake hard or steer sharply. A sudden input could complete the roll or throw the load further. Ease off the accelerator smoothly and reduce speed gently.
2. Straighten up and stop as soon as safely possible - exit the roundabout, find a safe place, and stop. Do not continue to the destination.
3. Inspect the load before moving again: check strap tension, pallet alignment, and whether any pallets are leaning or displaced.

Why continuing is unacceptable:

• The load has already moved. Once a stack leans, its centre of gravity is now outboard and higher relative to the restraint, so the next curve needs less lateral acceleration to tip it. The margin has shrunk.
• Base-only straps do not restrain the top of a 2.8 m stack. The upper pallets can move independently; a strap at the base holds the bottom while the top walks.
• Unwrapped pallets can slide against each other, and a single shifted column can cascade.
• If the load shifts further, it can cause a rollover or shed onto the road, endangering other traffic.

Correct decision: stop, secure or reload the stack (wrap, re-stack, add upper restraint), and only then continue. Report the incident and the restraint deficiency.

Restraint changes:

• Restrain the whole stack, not just the base. Use rated straps or curtains that bear on the upper portion, or wrap the pallets so each column acts as a unit.
• Shrink-wrap or band pallets so individual cartons cannot slide.
• Use headboards/gates or dunnage to prevent forward and lateral movement.
• Calculate restraint capacity against the load mass and the forces in braking and cornering - base straps alone are insufficient for a 2.8 m stack.
• Re-check tension after the first few kilometres.

Driving changes:

• Reduce speed further in curves and roundabouts; treat the sign speed as a maximum for low-CG vehicles, not a target.
• Smooth steering and braking inputs; avoid simultaneous braking and turning.
• Watch mirrors through curves for load movement.
• Plan routes to minimise tight, off-camber, or heavily banked curves.

Chain of responsibility:

• The loading party/consignor must ensure the load is packed, stacked, and restrained so it can be transported safely; loading a 2.8 m unwrapped stack with base-only straps is a loading deficiency.
• The operator must provide adequate restraint equipment and instructions.
• The driver must check the load before departure and refuse to proceed if restraint is inadequate.

Responsibility is shared: the driver's pre-trip check should have caught the base-only restraint, and the loader should not have presented the load that way.