The study consists of four separate experiments conducted in the VTI driving simulator. The common theme was to investigate how driver behaviour and traffic safety are influenced when the driver attends to another technical device while driving. The experiments were concerned with hands-free or hand-held mobile phone conversation and dialling, receiving mobile phone SMS messages and watching a DVD film (the latter two being minor pilot experiments). In three of the experiments (mobile phone conversation, SMS, DVD) the participants drove a route which led through urban and rural environments, ranging from 90 km/h rural to 50 km/h urban environments. The urban environments differed in complexity (three levels). The driving distance was about 70 km. The dialling experiment used a rural environment with a speed limit of 110 km/h. The driving distance was about 15 km. In the main experiment dealing with mobile phone conversation, a number of driving performance measures were analysed: driving speed, variation in lateral position, deceleration, brake reaction time, headway, time to collision, etc. PDT (Peripheral Detection Task) was used as a measure of mental workload. Mobile phone conversation was found demanding in terms of mental workload. It also had effects on driving. Most effects were quite similar for the two phone modes (hands-free, hand-held). Impaired reaction time performance was demonstrated in one of the situations for hand-held mode. However, effects were found which could be interpreted as attempts to compensate for the increased workload caused by the mobile phone conversation: speed was reduced (more so for hand-held than for hands-free mode), and time and distance headway increased. In spite of these compensatory behaviours, mental workload was still markedly increased by phone use. In the SMS experiment the participants braked later in one situation when reading the SMS message. No other effects were found in this minor experiment. In the DVD experiment, mental workload increased when watching the film, although this was compensated for to some extent by the increased distance headway to a lead vehicle. No compensation in terms of reduced driving speed, however, was apparent in this experiment. In the dialling experiment negative effects on traffic safety were evident from the larger variance of lateral car position during the dialling task for the hands-free phone mode. The mental workload also increased with the dialling task. Compensation in terms of reduced driving speed was apparent for both phone modes. Other aspects of mobile phone use while driving still remain to be analysed in more detail, such as starting or finishing a call, looking for a phone number to dial, mishaps like dropping the phone, etc. (A) This report is also available via Internet at URL: http://www.vti.se/PDF/reports/M969A.pdf
Abstract