Speed adaptation

A variety of effective means exist to reduce vehicle speeds – including the setting of speed limits according to road function, better road design, and the enforce­ment of limits by the police, radar and speed cam­eras. Speed limitation devices in vehicles can assist this process, by controlling the maximum speed a vehicle can travel at; some devices are able to set variable limits.

Insurance statistics show that high-speed cars – those with powerful engines, high acceleration and high top speeds – are more frequently involved in crashes than cars with lower speed capacities. The increase in maximum speeds in the past 30 to 40 years has made it increasingly easy to drive at inappropriately fast speeds, thus counteracting the effects of measures aimed at improving the safety of cars.

Intelligent Speed Adaptation (ISA) is a system being developed that shows great promise in terms of its potential impact on the incidence of road casualties. With this system, the vehicle “knows” the permitted or recommended maximum speed for the road along which it is travelling.

The standard system uses an in-vehicle digital road map onto which speed limits have been coded, combined with a satellite positioning system. The level at which the system intervenes to control the speed of the vehicle can be one of the following:

— advisory – the driver is informed of the speed limit and when it is being exceeded;

— voluntary – the system is linked to the vehicle controls but the driver can choose whether and when to override it;

— mandatory – no override of the system is possible.

The potential reduction in the number of fatal crashes for these different types of systems has been estimated to be in the range 18–25% for advisory systems, 19–32% for voluntary systems, and 37–59% for mandatory systems. Speed limit information can in theory be extended to incorporate lower speeds at certain locations in the network and – in the future – can vary according to current network conditions, such as weather con­ditions, traffic density and the presence of traffic incidents on the road.