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) choice within ISA could affect both driving behaviour and acceptance. An experiment was carried out in the TNO driving simulator. The HMI, the way information about speed limits was presented, was both visual and haptic. The visual information was an indication of the speed limit on the speedometer, presented permanently during the ISA runs. The haptic information consisted of an active gas pedal that generated an increased counter force to inform the driver that the speed limit was reached or exceeded. The three conditions of haptic information were a 'low force' active gas pedal (informative in nature), a 'high force' active gas pedal (more compulsory in nature), 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. On rural roads the reduction in speed due to the high-force ISA was larger compared to the low-force ISA. The standard deviation of the free-driving speed also decreased, but only on urban roads. With respect to free-driving speed in sharp curves, ISA (low-force and high-force) only had a marginally significant effect on the mean free-driving speed. ISA did also reduce speed on lower limit sections. On rural road with lower limit the reduction in speed due to high-force ISA was larger than it was for low-force ISA, on urban roads the reduction due to low-force ISA was larger. The results of the 85th percentile of the free-driving speed showed the same pattern as for the mean of the free-driving speed. With respect to workload, participants reported a higher workload for the high-force ISA than for the low-force or no ISA. Furthermore, compared to high-force ISA, participants found low-force ISA more pleasant, more likeable, more assisting, and more desirable. The reduction of the free-driving speed due to the high-force ISA, and the absence of clear indications of compensatory behaviour show that high-force ISA has a more positive effect on driving behaviour than low-force ISA, and low-force ISA has a more positive effect than no ISA. With respect to self-reported workload and acceptance, participants had a higher workload and a much more negative attitude towards the high-force ISA than they had towards low-force ISA. A trade-off between effectiveness and acceptance occurs: the low-force ISA had a neutrally or positive effect on speed and a neutral effect on acceptance, whereas the high-force ISA had a larger positive effect on speed, at the price of a reduction in acceptance. (Author/publisher)
Abstract