Conversations in cars: the relative hazards of mobile phones

The aim of this study was to benchmark the distraction caused by hands-free mobile phone conversations in relation to other conventional in-car tasks, and to similar conversations held with a front seat passenger. Thirty experienced drivers aged between 21 and 64 years drove a 17 km route in the TRL driving simulator for each experimental condition. The results showed a complex but consistent picture of distraction. Measures of car following ability and general measures of speed control showed that all additional conversation and in-vehicle tasks produced more variable performance consistent with the additional load imposed. Self report subjective workload measures showed that both in-vehicle and passenger conversation tasks were rated equally more difficult than baseline driving. Handsfree conversations were rated yet more difficult. This pattern was repeated in results of choice reaction time tasks. When drivers were required to respond selectively to road signs, it was shown that the best performance was achieved in the driving baseline condition, with a significant deterioration to in-vehicle and passenger conversation conditions, and yet further deterioration in the handsfree conversation drive.The act of driving was shown to have a distinct effect on the quality and character of a conversation. The rate of talking, the number of pauses, number of errors and performance on verbal and numerical reasoning tasks all deteriorated when driving at the same time. Comparison was made between the conversations held over the carphone and with the front seat passenger. There was a clear difference on all conversation measures showing that performance was worse when the response was via the handsfree carphone.It is concluded that hands-free phone conversations impair driving performance more than these other common in-vehicle distractions.(A)