Multiple chronic medical conditions and associated driving risk: a systematic review.

BACKGROUND: Numerous medical conditions can affect one's ability to operate a motor vehicle. The likelihood of having multiple medical conditions increases with advancing age; however, the interplay of the associated impairments has not been previously addressed in the literature.
OBJECTIVE: To identify the incremental risks for the effects of multiple chronic medical conditions on driving ability and crash risk.
METHODS: A comprehensive English-language literature search using the keywords driving, motor vehicle crashes, accidents, multiple medical conditions, and chronic medical conditions was completed. To be included, the article had to address the effects of the combination of multiple chronic medical conditions on driving and include a relevant outcome, such as crashes, driving violations, on-road driving assessment, driving simulator assessment, or driving cessation/avoidance patterns.
RESULTS: The overall trend was for increasing number of chronic medical conditions to be associated with higher crash risk and higher likelihood of driving cessation. Although there is some evidence that impaired functional abilities are associated with poorer driving outcome, most of the studies do not support this. No studies were identified that evaluated compensation techniques for drivers with multiple chronic medical conditions with the exception of driving avoidance or self-restriction.
CONCLUSIONS: The evidence supports the view that drivers with more chronic medical conditions tend to cease driving or engage in driving avoidance. The myriad combinations of diseases and disease severity present a level of complexity that complicates making informed decisions about driving with multiple chronic medical conditions.