Mobile telephone use among Melbourne drivers: a preventable exposure to injury risk

In reply: McEvoy and Stevenson raise some important issues. The first relates to the confusion between driver impairment and crash risk. Intuitively, this association seems valid, as any level of driver impairment could be expected to affect driving skill. However, they are correct to suggest that the two should not be used interchangeably without supporting evidence.

Secondly, I agree that the quality of evidence directly linking mobile phone use with crash risk is poor.1-4 This largely relates to the difficulty in confirming mobile phone use at the exact time of the crash. Reported direct observation is uncommon, billing records are inexact, and self-report may be subject to prevarication bias.

The use of hands-free devices was not examined in our study, mainly because of difficulties in detecting their use. There is anecdotal evidence of a trend towards the use of these devices while driving. However, while their use might avoid the need to physically hold the phone, they may not significantly diminish driver impairment resulting from distraction.

Many questions remain, and I encourage McEvoy and Stevenson in their endeavour to more clearly evaluate the real-world risk of mobile phone use, both handheld and hands-free, by drivers.

Chalker et al draw attention to the comparison of crash risk for mobile phone use while driving and drink driving. I acknowledge that interpretation of published studies is confusing. Redelmeier’s statement that alcohol circulates for hours and that a telephone call may last for only minutes relates to individuals. From the highway perspective, when one driver completes a call, another is likely to be starting one and effectively assuming the increased collision risk. This concept is consistent with our findings. Almost 2% of drivers were using mobile phones when they passed our observation points, and were therefore at risk at that time. The exact extent of this risk awaits clarification. Chalker et al provide US alcohol and mobile phone related crash statistics. Unfortunately, the latter were not referenced and their value is therefore questionable.

Finally, Chalker et al are to be commended for publishing safety tips for mobile phone use while driving. However, their claim that common-sense practices can make mobile phone use safe is extraordinary and disregards emerging evidence. Indeed, this statement appears to contradict their first safety tip, which states “a hands free device can reduce the physical effort to make and receive calls; however, it alone doesn’t make using a mobile phone while driving safer”.5 At best, therefore, common-sense practices will not make mobile phone use while driving safe, only possibly safer.