Disengagement

A disengagement is an event in which a human (a safety operator on board, or a remote-assistance specialist) takes control of an autonomous vehicle that was operating in driverless mode. The California DMV requires test-permit holders to publish annual disengagement counts broken down by mileage and cause, making disengagement rate one of the few comparable cross-company autonomy metrics in the public record. Distinct from a "safety event" (an actual [incident](/glossary/incident)) and from a "ride completion failure" (a stranded vehicle).

The distinction matters because disengagement counts are routinely cited as autonomy progress without accounting for what triggered them. A disengagement caused by the vehicle proactively stopping in a low-risk safety-margin-correct way is structurally different from one caused by perception failure. Waymo's published reporting distinguishes by cause; some other reporting does not. The headline "X disengagements per Y miles" comparison usually elides the difference that actually matters.