A naturalistic, on-road study using instrumented vehicles was conducted to: 1) to assess the effects of wireless phone use while driving on driver distraction and driving performance as a function of wireless phone interface type (i.e., hand-held, conventional hands-free, and enhanced hands-free with voice dialing), and 2) to characterize the conditions under which drivers elect to use wireless phones. Ten participants drove instrumented vehicles for 2 weeks with each of three wireless phone interface conditions. Driving performance and eye glance activity were measured during wireless phone use and baseline driving. The hand-held interface was associated with more calls, calls of longer duration, and shorter dialing periods than the hands-free interface. More than half of calls made in the voice dialing interface condition were dialed manually despite instructions to use voice dialing, suggesting drivers found voice dialing difficult to use. Drivers engaged in fewer calls when driving in conditions of high traffic density, particularly when using the hands-free phone interfaces. Overall, the robustness of eye glance data provided useful information regarding drivers’ glance behavior during conversations and how this glance behavior can change as the conversation progresses in time. Drivers spent 21 percent less time glancing at the forward roadway during hands-free voice dialing than during baseline driving. Drivers spent proportionately more time looking at the road ahead during phone conversation (all interfaces) than during baseline driving. Drivers made more glances away from the forward roadway while talking on a hands-free wireless phone than while talking using a hand-held interface. Drivers glanced frequently at the hands-free wireless phone equipment during conversation, despite that there was no functional need to direct their glances or head toward the equipment. During longer conversations (2 minutes duration or greater), the percent of time spent looking at the forward roadway increased steadily. This may indicate that drivers become more cognitively engrossed in the conversation as it progresses, which could lead to a “looked but did not see” situation. The percent of time that participants were observed driving with two hands on the steering wheel was quite low. During baseline driving, participants steered using only one hand 87 percent of the time. Drivers spent proportionately more time steering with two hands during hands-free conversations than during hand-held conversations. The percentages during hands-free conversation (13-16 percent) were similar to those observed during baseline driving (13 percent), however, the corresponding percentage during hand-held conversation was less than 1 percent. While some differences were found between phone interfaces for dialing and conversation durations, significant differences in driving performance were not found. Similarly, driving performance measures did not exhibit differences between phone conversation and baseline driving. Given that these analyses have demonstrated a large amount of variability in driving conditions and based on the fact that many studies have shown performance degradation due to conversation generally, the absence of such affects in this study suggests that the experiment did not have the sensitivity necessary to detect differences in driving performance due to the interface conditions. (Author/publisher)
Abstract