Disengagement

A disengagement occurs when a self-driving system hands control back to a human, or a human takes over, because of a failure, an unsafe situation, or caution. California's Department of Motor Vehicles requires companies testing autonomous vehicles there to report their disengagements each year.

Disengagement counts were long used as a rough comparison of how often systems need help. Companies define and record them differently, and vehicles without a driver on board may instead rely on remote assistance, which is not always counted.

Fewer disengagements per mile can reflect better software, easier routes, or different reporting practices. On their own, they are a weak measure of safety.