Mobile phone use – effects of conversation on mental workload and driving speed in rural and urban environments

The study was concerned with the effects of mobile phone conversation on simulated driving in different traffic environments. Forty-eight participants drove a distance of 70 km on a route which led through different environments. The environments were: rural environment with a speed limit of 90 km/h, rural environment with a speed limit of 70 km/h, urban environment of low complexity, urban environment of medium complexity and urban environment of high complexity. The experimental design was mixed with phone mode (handsfree/handheld) as a between-subjects factor and phone use (yes/no) and traffic environment as within-subjects factors. Performance on a peripheral detection task (PDT) – a measure of mental workload – presented while driving, was impaired by mobile phone conversation in all environments. PDT performance was, however, remarkably poor at the complex urban environment, even when the participants were not using the phone. Driving speed was reduced by conversation in all environments for handheld mode, but only in two environments for handsfree mode – the rural environment with a speed limit of 90 km/h and the complex urban environment. The effects on speed could be interpreted as a compensatory effort for the increased mental workload.