What is ISA?

Intelligent Speed Adaptation (ISA) is the generic name for advanced systems in which the vehicle "knows" the speed limit and is capable of using that information to give feedback to the driver or limit maximum speed.

An ISA system can be characterised by how intervening (or permissive) it is.

1. Advisory

display the speed limit and remind the driver of changes in the speed limit.

2. Voluntary

allow the driver to enable and disable control by the vehicle of maximum speed.

3. Mandatory

the vehicle is limited at all times.

Another dimension for differentiating ISA systems is that of the currency of the speed limits themselves.

1. Fixed

the vehicle is informed of the posted speed limits;

2. Variable

the vehicle is additionally informed of certain locations in the network where a lower speed limit is implemented. Examples could include around pedestrian crossings or the approach to sharp horizontal curves. With a Variable system, the speed limits are current spatially.

3. Dynamic

Aditional lower speeds are implemented because of network or weather conditions, to slow traffic in fog, on slippery roads, around major incidents, etc. With a Dynamic system, speed limits are current in terms of time.

(source: Oliver Carsten, Leeds University, United Kingdom)

How does it work?

The concept of ISA are based on digital maps in relation to vehicle positioning information, e.g. through GPS. They are also based on the possibilities of vehicle-roadside communication and the automatic detection of the actual traffic, road and weather circumstances. Some systems are already available and likely to be introduced progressively. With respect to speed management, there are interesting and promising developments related to ISA and dynamic speed limits.

A method and apparatus for reporting a posted speed limit to the driver of a vehicle is disclosed. The position of the vehicle is determined using a GPS receiver or triangulation of cellular telephone signals. The position is used to retrieve speed limit or other information from a database. The information is then reported to the driver. A technique is also disclosed for comparing the actual speed of the vehicle with the posted speed limit and issuing a warning to the driver when the posted speed limit is exceeded.

Intelligent Speed Adaptation (ISA) is an in-vehicle system that uses information on the position of the vehicle in a network in relation to the speed limit in force at that particular location. ISA can support drivers in helping them to comply with the speed limit everywhere in the network. This is an important advantage in comparison to the speed limiters for heavy good vehicles and coaches, which only limit the maximum speed.

What can ISA do for Road-safety?

Several trials were held or are still proceeding. A main conclusion is that ISA can result in a reduction of 25-30% in the number of (serious) injuries if a) it is generally introduced and working, and b) the system ensures that nobody drives faster than the present speed limits. More experiments and large scale practical evaluations will increase the insight into the actual extent of the effects of this very promising system.

Some main results can be read in these brochures of the swedish trial.

See the report about ISA and road-safety (mostly in Dutch, some comments in English).
(VRT/ CANVAS: 'TerZake' 9 april 2001; NL)