Intelligent Speed Adaptation: A Review

The implementation of Intelligent Speed Adaptation (ISA) has the potential to significantly reduce the incidence and severity of road trauma in Australia and overseas. Over the last few years there has been a growing interest in ISA, which is reflected in the growing number of ISA research and demonstration trials taking place all over the world. European countries such as Sweden, the Netherlands and the United Kingdom have to date been at the forefront of research into ISA. However, more recently, countries such as Denmark, Finland, Australia, France, Belgium, Spain and Japan have also taken an interest in ISA. This paper provides an up to date review of the literature and trials involving ISA from around the world, with particular emphasis on evaluating the potential road safety benefits and human factors issues associated with the different variants of ISA. Speeding is known to be a contributing factor in a large proportion of crashes involving vehicles in Australia. Of the various classes of ITS that are reaching technical maturity, the technology that stands out as having great immediate potential to reduce the incidence and severity of road trauma in Australia and overseas is Intelligent Speed Adaptation (ISA) (Regan, Oxley, Godley & Tingvall, 2001). Intelligent Speed Adaptation is a generic term for a class of ITS in which the driver is warned and/or vehicle speed is automatically limited when the driver is, intentionally or inadvertently, travelling over the posted speed limit for a given location. Specifically, ISA systems compare the current speed and position of the vehicle with the local posted speed limit and respond if the vehicle exceeds this posted limit. In this paper we provide a current review of what is known about ISA and its potential to enhance road safety. The material reported here is derived from a more comprehensive review of the literature on ISA undertaken by the Monash University Accident Research Centre (MUARC) for Austroads (Regan, Young & Haworth, 2002). The more comprehensive review constitutes the first phase of a multi stage project that is expected to culminate in an on-road study that will evaluate the effectiveness of ISA for heavy vehicles in Australia. Intelligent Speed Adaptation There are two main classes of ISA: speed alerting and speed limiting systems. Speed alerting systems warn the driver if he or she is exceeding the posted speed limit in a given location. While there are many variants of speed alerting systems, the two most common ones are: an "informative" variant, in which the driver is provided with visual and auditory warnings if they exceed the posted speed limit beyond a specified threshold, and an "actively supporting" variant, in which the driver receives a "haptic" warning (with or without a preceding visual warning) in the form of increased upward pressure on the accelerator pedal. This resistance is designed to inform the driver that they are currently exceeding the posted speed limit for their given location (Varhelyi, 2001a). Variable speed limiting devices make it impossible for the driver to exceed the posted limit. The maximum speed of the vehicle is limited to different speeds at different locations depending on the posted speed limit. A number of control mechanisms exist to restrict a vehicle to the posted speed limit. These generally consist of two types: speed governors and speed retarders. For both variable speed alerting and limiting systems, the maximum speed at which the vehicle can travel before the ISA warnings are activated depends on the posted speed limit for the location in which the vehicle is travelling. Information regarding the current position of the vehicle and the speed limit that applies to that location can be obtained in one of two ways. One way is by means of electronic signals to the vehicle from beacons or transmitters attached to speed signs or other roadside infrastructure, such as lampposts. An alternative approach, and the one that is being adopted most widely in ISA trials around the world, utilises global positioning system (GPS) technology. With this approach, information regarding the road network and data about the posted speed limits within it are stored in a digital map database within the vehicle. A GPS receiver fitted to the vehicle locates vehicle position. An on-board computer continuously analyses the location of the vehicle and compares the posted speed limit with the current speed of the vehicle. Warnings are issued when the vehicle is exceeding the speed limit or some other nominated speed threshold for a given location (van Boxtel, 1999). Development and Deployment of ISA Systems in Australia The Transport Accident Commission (TAC) SafeCar Project is to date the only Australian study concerned with the design, development, deployment and evaluation of ISA technologies. It is a joint research project involving the TAC, the Ford Motor Company of Australia and the Monash University Accident Research Centre. The overall aim