Such circumstances can be especially hazardous for tractor/semi-trailer combinations, where even momentary loss of control by the driver could lead to roll over or jack-knifing.

The new Scania ESP stability program makes a big contribution to safety by monitoring key stability parameters and automatically triggering appropriate controls. The system is available on all 4x2 tractors equipped with disc brakes with electronic control. It is designed to work on wet or slippery roads (the aim being to prevent jack-knifing resulting from either oversteer or understeer conditions) and on dry roads (where the main risk is roll over resulting from excessive speed or adverse camber on bends).

The system has sensors that measure lateral acceleration at the vehicle’s centre of gravity. If lateral acceleration exceeds a predetermined limit, the the engine torque is cut and wheel brakes are applied. In extreme circumstances, full emergency braking to the tractor and trailer may occur. 

The system is able to detect driver reaction by comparing the yaw angle with the steering angle. If these do not correspond, engine torque is cut and wheel brakes applied to stabilise the truck. Precisely which brakes are activated (on which wheels and which axles) depend upon the nature of instability.

The system also has a switch-off mode. This is for trucks that ordinarily have a high centre of gravity when fully laden, but very low when unladen. This feature eliminates the risk of inappropriate triggering in the unladen condition.

When ESP is triggered, data is stored within the system’s memory. Frequent triggering indicates a need for driver training.