[duskwuff]

> What is the rationale for reporting death rates in terms of vehicle-years, rather than rate per mile traveled?

Vehicle-years can be determined directly from vehicle registration data. Miles traveled would require a lot more guesswork.

[dredmorbius]

With the increasing prevalence of smog checks as a registration renewal requirement, and the inclusion of a highly detailed electronic vehicle record (see for example California's BAR-90 and subsequent records, Washington and several other states have similar records), odometer data is available and is used heavily by insurance companies in assessing risk for a large number of drivers.