On-Road Comparison of Driving Performance Measures When Using Handheld and Voice-Control Interfaces for Mobile Phones and Portable Music Players

Abstract

This study presents an on-road evaluation of driver performance when controlling in-car technology via a handheld or voice-controlled interface. Participants drove with an experimenter on public roads while making mobile phone calls, having brief phone conversations, and playing tracks from a portable music player using both types of interface. The test vehicle was an instrumented 2010 Mercury Mariner equipped with the Ford SYNC® system, which allows for voice control of mobile phones and portable music devices. Twenty-one participants were tested, including 12 younger (19-34) and 9 older (39-51). All participants were owners of a vehicle equipped with the voice-control system, and all used the system regularly for phone calls and music playback. Results indicated that handheld dialing and music track selection tasks were of longer duration and were associated with more frequent and longer glances to the interior of the vehicle, more total glance time to the interior of the vehicle, higher steering variance and maximum steering wheel velocity, and higher subjective mental demand than when using voice control for the same tasks. These differences were not found for conversation tasks. All tasks had higher mental demand than baseline driving. Further, older drivers had more difficulty maintaining vehicle tracking when dialing and playing tracks using handheld controls, as seen in steering variance and maximum steering velocity data. These findings suggest that voice control of in-vehicle devices may allow drivers to keep their eyes on the road longer, track their course more consistently, and have lower mental demand than when these devices are controlled manually.