The project PROSPER (Project for Research On Speed adaptation Policies on European Roads) was initiated to find answers concerning efficiency, public support, and implementation of road speed management methods, particularly Intelligent Speed Adaptation (ISA) in Europe. The PROSPER project was funded by the European Commission within the 5th Framework Programme. Part of the PROSPER project was to examine how Human Machine Interaction (HMI) design within ISA could affect both driving behaviour and acceptance. An experiment was conducted in the TNO driving simulator. The HMI, the way information about speed limits was presented, was both visual and via the gas pedal. The visual information was an indication of the speed limit on the speedometer, presented permanently during the ISA runs. The gas pedal had two functions: one was a tactile pedal, that informed the driver about a speed limit violation by means of vibration, second was a dead throttle, i.e. a pedal that loses its function above the speed limit (similar to a speed limiter). The three conditions were ISA with a tactile gas pedal, ISA with a dead throttle, and a condition with no ISA. Driving behaviour and workload were registered in two road environments: an urban and a rural road. The use of ISA resulted in a reduction of the mean free-driving speed compared to driving without ISA. The reduction in speed on rural roads due to the dead throttle was larger compared to the tactile pedal ISA. The standard deviation of the free-driving speed was decreased for both pedals. With respect to free-driving speed in sharp curves, ISA (tactile pedal and dead throttle) had no effect on the mean free-driving speed. ISA did also reduce speed on lower limit sections. On the rural road the reductions on the 70 km/h speed limit showed the same pattern as on the 80 km/h speed limit. On urban roads the reduction on the 30 km/h speed limit due to the tactile gas pedal and the dead throttle were larger than on the 50 km/h speed limit. With respect to workload, the overall NASA workload index showed no differences between the three conditions. Furthermore, compared to the tactile pedal, participants found the dead throttle more sleep inducing. The free-driving speed was reduced both by the tactile pedal and the dead throttle. The dead throttle reduced the speed more than the tactile pedal did. Also the standard deviation of the free-driving speed was reduced by ISA, most by the dead throttle. There were no clear indications of compensatory behaviour. It can therefore be concluded that the dead throttle has a more positive effect on driving behaviour than the tactile pedal. With respect to self-reported workload and acceptance, there was no difference in workload between no ISA, the tactile pedal and the dead throttle. Participants had a slightly more negative attitude towards the dead throttle than they had towards the tactile pedal. A trade-off between effectiveness and acceptance occurs: the tactile pedal as an informative system with a positive effect on driving behaviour or the dead throttle with a more positive effect on driving behaviour, but slightly less accepted. (Author/publisher)
Abstract