Intelligent Speed Adaptation
Around 70% of rural crashes on bends occur on curves that can only be safely negotiated at speeds considerably lower than the posted speed limit.
New Zealand uses recommended speed signage to signal drivers that they are approaching a significant curve to try to reduce this crash rate, however compliance with the recommended speeds is low. NZTA wanted to examine the benefits of using GPS technology to increase driver compliance with the recommended speed.
Intelligent Speed Adaptation (ISA) systems have been widely used and evaluated in overseas contexts and shown to reduce speeding behaviour. These systems use GPS information to inform the driver of their speed relative to the speed limit, with feedback to the driver varying from visual and audio response to limiting the speed of the vehicle. As significant investment would be needed to implement an ISA system in New Zealand, proof of its benefits and an evaluation of the costs involved in a local context were required.
WSP Opus was part of a project funded by NZTA which examined the use of ISA systems in New Zealand, in conjunction with collaborators from MWH and the University of Leeds. The focus of this research was a version of ISA that provides recommended speeds for specific curves, as well as speed limit information. The premise was to determine how drivers responded to having the technology in their cars and what difference it made to their driving behaviour.
Our team focussed mainly on user acceptance of the technology, the effect on driver behaviour, and any legal barriers to introducing an ISA system in New Zealand (such as legal challenges to Police speed measurement and enforcement). Focus groups were used to determine what people want from ISA systems, how they would like them to be designed, and what incentives might encourage their use.
Road trials on both urban and rural roads showed that drivers responded well to the technology, driving below the speed limit 7% more of the time overall when using the ISA device, and reducing speed to within 15km/h of advisory speed limits a further 7% of the time. Feedback showed drivers would prefer greater customisability of the information provided by the ISA device, and a better alignment between this information and natural driving styles; for example, the system did not allow for early acceleration out of curves. The research provided NZTA with suggestions on how to make the technology acceptable to the driving public. But most importantly, it provided evidence that ISA technology could have a positive impact on driver behaviour and in reducing crashes.