recognised that the speed limit databases used in ISA systems should ideally take account of posted advisory speeds as well as posted maximum speed limits. The New South Wales ISA trial in the Illwarra region south of Sydney currently is the only trial to post advisory speeds as well as posted maximum speed limits. Some car manufacturers have expressed concern that some types of speed limiters take control away from the driver. Some ISA systems do have provision for over-ride by the driver in the event that the set speed is inappropriate. For some traffic safety practitioners, active intelligent speed adaptation is thought to be an example of 'hard automation', an approach to automation that has been largely discredited by the Human Factors community. An inviolable characteristic of human users is that they will adapt to these systems, often in unpredictable ways. Some studies have shown that drivers 'drive up to the limits' of the system and drive at the set speed, compared to when they are in manual control, where they have been shown to slow down. Conversely, the experience of some drivers with driving under an active ISA system has been that they find they can pay more attention to the roadway and road environment as they no longer need to monitor the speedometer and adjust their speeds on a continuing basis. Intelligent speed adaptation has also been held as an example of a technology which, like speed cameras, can alienate some drivers, forming a significant barrier to its widespread adoption. Some studies which pre-date the development of ISA systems indicated that drivers make relatively little use of the speedometer and instead use auditory cues (such as engine and road noise) to successfully regulate their speed. ISA regulations may prompt the disappearance of models that cannot be re-designed to accommodate the necessary sensors. For example, Toyota's GR86 will go off sale in Europe after 2024, as its existing roofline cannot accommodate an ISA sensor. If speed signs are not present, an ISA system may be unable to function. This is a particular problem when exiting a side road onto a main road, as the vehicle may not pass a speed sign for some distance. Driving between alternate countries using metric and imperial systems may be a further challenge. Benefits A British study estimates that ISA could reduce fatalities by half. RTA (NSW Australia) ISA trial results showed the