Objective:​ This study used a driving simulator to investigate the effect of using a Bluetooth hands-free cellular phone earpiece on the driving behavior of two age groups.

Methods:​ Forty-eight participants (24 aged 20–26 and 24 aged 65–73) were examined to assess their performance on the following divided-attention tasks under 2 driving load conditions (high and low):​ (1) attempting to maintain the speed limit and (2) using a cellular phone while driving. The length of the call conversation (long vs. short) and the conversational content (complex vs. simple) were manipulated as within-subject independent variables. The driving behavior of the participants, their task reaction times and accuracy, and subjective ratings were collected as dependent variables.

Results:​ The results indicate that under low driving loads, short talk times, and simple conversational content, the driving behavior of the participants showed low variance in the vehicle's mean speed. In contrast, complex conversation had a significantly negative impact on driving behavior. Notably, under a low driving load, motorists’ driving behaviors, measured in lateral acceleration, caused significantly smaller variance in complex conversations compared to no call and simple conversations. The use of a hands-free cellular phone affected the performance (acceleration, lane deviation, reaction time, and accuracy) of older drivers significantly more than younger drivers. While performing divided attention tasks, the accuracy of the older drivers was 66.3 percent and that of the younger drivers was 96.3 percent. Although this study did not find a clear impact of cellular phone use on the driving behavior of younger drivers, their divided-attention task reaction times and accuracy were better under no-call than calling conditions.

Conclusions:​ This study indicates that the use of hands-free cellular phones could significantly affect the safety of driving among the older and present risks, although lesser, for younger drivers.