What is a disengagement in a self-driving car?

How it works

California put a definition into its regulations. Before the state rewrote its testing rules in 2026, it was in section 227.50 of its vehicle regulations. Cornell's Legal Information Institute showed that text in October 2026. The section defined a disengagement as the autonomous mode being deactivated when a technology failure is detected or when safe operation requires the test driver to take manual control immediately. For vehicles with no driver on board, it covered cases where safety required deactivating the technology.

Every company testing on public roads had to send the Department of Motor Vehicles (DMV) an annual report by January 1 covering the year to November 30. The report summarized the disengagements, including the type of location, the cause and who initiated each one, plus the miles each vehicle drove in autonomous mode each month.

Why it matters

The DMV released the reports, and researchers used them. A 2016 study in PLOS One drew on reports covering 460,097 autonomous miles driven from September 2014 to November 2015. It found test drivers took 0.83 seconds on average to take control.

The measure has drawn criticism. TechCrunch noted in January 2025 why the reports had been controversial. It said companies did not apply the same standards, so results could not be compared. The DMV's statement of reasons for its 2026 rules says the old requirement swept in precautionary and routine interventions and did not provide meaningful safety insights. Industry commenters, it says, argued that disengagements frequently happen for routine or discretionary operating reasons that do not necessarily indicate a system failure.

Where things stand in 2026

California's rules no longer require these reports. The statement of reasons says disengagement reporting was eliminated. The new testing regulations set different measures. Companies testing with a safety driver must file monthly reports of each time the driver took over in response to a system failure. That is defined as a malfunction that keeps the automated driving system from reliably doing its part of the driving. Driverless testers report vehicle immobilizations: stops in an active travel lane where the vehicle cannot continue and must be retrieved or driven by a person.

A DMV memo dates the new reporting rules to April 28, 2026. It sets August 26, 2026, as the start of monthly reporting. The statement of reasons says the new requirement focuses on system reliability and safety-critical failures.