Abstract
The voice-input interfaces of digital assistant devices are expected to reduce influences on the driving behaviors than visual-manual interfaces, though impacts of voice-input tasks are not sufficiently clear. This study examined the influences of the digital devices use during driving on the vehicle position variability through comparing the vehicle lateral displacement and headway distance. As the results of a driving experiment on a proving ground, following properties were clarified; (1) variability of vehicle position increased as a function of manual steps and voice inputs of digital device tasks, (2) small size of visual display deteriorated the visual behavior and subjective ratings, (3) digital device tasks impaired the driving behaviors if the tasks required longer total glance time exceeding 8 seconds. It was also revealed the voice-input task increased the variability of headway distance, in contrast to the visual-manual tasks harmed variability of both lateral displacement and headway distance. This result suggests the voice-inputs operation can reduce drivers' processing resources and it deteriorates coping behaviors to the relatively less conspicuous on-road events.
