As as example, the measurement of exposure is very important in older drivers. Studies have found that many individuals maintain drivers licenses, but do not drive. Their exposure, then, is nil. Many older persons voluntarily stop driving. A study by Marotolli found several reasons related to this decision. These include getting older, becoming functionally limited, and certain medical conditions.

Marottoli RA, et al. Driving cessation and changes in mileage driven among elderly individuals. Journal of Gerontology: Social Sciences 48(5):S255-260, 1993