Semi-autonomous driving: do drivers still respond to unexpected events?

This paper reports a study about driving a semi (longitudinal control) and highly (longitudinaland lateral control) autonomous car. In a 30 minute simulator drive, the driver encounterednormal and critical events. In total, 43 participants took part in three conditions (control, semiand highly autonomous). The results show that the semi and highly automated systems wereactivated about 80% of the time, especially on undivided highways and rural roads. Peoplewith either system drive slower, with a lower standard deviation of speed, drive more in themiddle of the lane with less swerving, even with the system that only provides longitudinalcontrol. No difference was found in gap acceptance, responding to sudden cars or traffic jams.The subjective evaluation shows some mixed results. Participants did not experience lessworkload when driving with one of the systems, and thought that driving without the systemwas easier. However, they also indicated that the system helped them respond more quickly todangerous situations and the majority of people indicated that they would like to have such asystem, and that they preferred driving with the system rather than without the system.