Assumed autonomous cars will be equipped with an advanced sensor technology that would allow them to travel with a short (only a few-centimeter) inter-vehicular distance. Passengers in autonomous cars and pedestrians are expected to feel discomfort and uneasiness with such an unfamiliarly short inter-vehicular distance. The aim of the present study was to examine the level of discomfort experienced by passengers inside autonomous cars and pedestrians outside them. Participants were twenty-four males and females whose age ranged from 20–75 years old. They regularly drove their car at least once a week. Participants were instructed to sit inside a vehicle simulating autonomous driving and to report their level of discomfort under three conditions, i.e., taking right turn at the cross-section with a pedestrian waiting to cross the road, going around a parked car on the street, parking backward right next to a parking car. Participants were asked to rate their discomfort under each condition with four varying distances. Participants were then asked to report their level of discomfort as pedestrians outside the vehicle under the same obstacle-avoidance conditions. The result of the study showed that both passengers and pedestrians felt more discomfort as the distances between the simulated autonomous car and the obstacle became shorter. When simulated autonomous cars avoided the vehicle parked on the street,passengers tended to feel greater discomfort than pedestrians did and that passengers less confident in driving felt greater discomfort than those more confident in driving. Based on the results, we calculated appropriate distances which autonomous cars should take from various obstacles. The study proposed a range of obstacle-avoidance distance in city area, which could be used as one of the design guidelines for autonomous driving. Revising these guidelines would be necessary in the future when autonomous vehicles will become more socially accepted, as people’s perceived discomfort level is expected to change.
