In-vehicle speed adaptation - On the effectiveness of a voluntary system

Sammanfattning: The overarching aim of this thesis is to study the long term effects of a voluntary speed adaptation system, the Active Accelerator Pedal (AAP), and its effectiveness for different driver types. The papers making up this thesis are based on a study carried out on 284 vehicles and drivers in the Swedish city of Lund from 1999 until 2002. The results showed that the AAP brought a significant reduction in both mean speed and speed variance, estimated to lead to a reduction in injury accidents of up to 25 % if all vehicles where equipped with the system. It was further found that drivers’ behaviour towards other road users improved, they showed a more correct yielding behaviour and were more likely to give pedestrians the right of way at zebra crossings. Moreover, the time gap to the vehicle in front increased slightly with the system. However, there were also signs of negative behavioural modifications in the form of drivers’ forgetting to adapt their speed to the speed limit when not supported by the system; this effect was not statistically significant though. These positive results augur well for in-vehicle speed adaptation, but this thesis found that the drivers in favour of the AAP were already without it driving at, or close to, the speed limit while those most negative to the system were the fastest drivers. It was further found that the speed-reducing effect of the AAP was lower for those who were negative to the system. The conclusion is that a voluntary system like the AAP will reduce inadvertent but not deliberate speeding. For such a system to reach its full potential, either peoples’ intentions have to be changed or the system has to be more intrusive, i.e. a mandatory limiting system.