Driving Dynamics, Load and Passenger Weight Distribution
Domain 4 combines driving dynamics with load and passenger weight distribution: how mass, centre of gravity and axle loads change braking, cornering and stability of a bus.
Dynamics
- Mass multiplies braking distance; keep larger gaps than in a car and brake early and progressively.
- A bus has a high centre of gravity and long overhangs. In tight turns the rear end swings out (tail swing) and the inner rear wheel cuts the corner - watch kerbs, poles and pedestrians.
- Side wind, especially on bridges and when passing lorries, pushes the tall body; reduce speed and hold the steering firmly.
- Downhill: use the retarder and a low gear, never coast in neutral; continuous service braking overheats and fades.
- Reversing needs a guide person; mirrors cannot cover the whole blind area.
Load and weight
- Limits: permissible total weight, axle loads, roof load and the vehicle's design class for standing passengers.
- Plan the load: heavy luggage low and between the axles, wheelchairs and prams secured with the designated straps, roof racks loaded only within the manufacturer's limit.
- Passenger distribution matters: a full standing area at the rear raises the rear axle load and lightens the front axle, worsening steering.
Worked example
Coach: permissible total 18,000 kg, front axle 6,500 kg, rear axle 11,500 kg; empty weight 13,400 kg. Payload is therefore 4,600 kg. Fifty passengers at 68 kg = 3,400 kg, luggage 1,100 kg = 4,500 kg, so the total is legal. But if most of that luggage sits behind the rear axle, the rear axle can reach its 11,500 kg limit while the front axle is light. Move luggage forward and check axle figures, not just the total.
Traps that cost marks
- Adding front and rear axle limits and believing that sum is the legal total.
- Treating standing passengers as weightless, or exceeding capacity because everyone "fits".
- Forgetting the trailer drawbar load.
- Loading roof boxes with heavy items and losing stability.