Heredity or Environment: Why is Automobile Longevity Increasing?

Over the past 25 years the longevity of automobiles has increased dramatically. We disentangle the rise in longevity into an embodied or inherent-durability effect and a disembodied effect (driven by the external environment, such as reduced accident rates or reductions in the prices of auto repair parts) and estimate these effects by year from 1950 through 1991. We find that the entire rise in auto longevity is due to some force disembodied from the cars themselves and offer some speculation about the nature of this external environment.