Can we talk about Speed? The Effect of Verbal Protocols on Driver Speed and Perceived Workload

摘要

In recent naturalistic driving studies, verbal protocols analysis (VPA) has become a popular method for assessing road users’ situational awareness and mental processes while on-road. This method requires participants to provide concurrent verbal protocols about the driving task. Despite its increasing use in road safety research, it is unknown whether providing verbal protocols influences driving behavior and performance. The aims of this study were to examine the effect of providing concurrent verbal protocols on speed regulation and perceived workload, and to determine whether these effects are moderated by practice. Twenty participants with a full license drove an instrumented vehicle around a pre-determined route, twice while performing concurrent verbal protocols and twice while driving in silence. The results indicate that performing concurrent verbal protocols does not have a significant impact on driving speed, speed variability, percentage of time spent over the speed limit or ratings of perceived workload. However, speed variability decreased significantly with practice driving the route. These findings suggest that performing verbal protocols does not disrupt driving performance as reflected in measures of speed, which supports the claim that VPA is an appropriate method for on-road studies. Further important research questions regarding validating the VPA method for on-road studies are discussed.