A self-driving car can change its automation level mid-journey
One car might count as Level 3 while keeping its lane on a highway below 100 km/h, then drop to Level 2 as it speeds up. SAE's widely used scale rates who carries responsibility in a given situation, not the vehicle itself, which is why the phrase self-driving still has no agreed definition.
SAE International published its six-step scale, running from fully manual Level 0 to fully automated Level 5, in 2014 as the standard J3016. America's road safety regulator adopted it after a 2016 revision, and a United Nations regulation based on it took effect in January 2021 and applies in more than 50 countries. Critics say the ladder wrongly implies automation grows in a straight line and that more is always better, and it ignores changes that roads and other road users might need.
The key idea is the operational design domain, the set of conditions a system is built for. At Level 3 and higher, a car must notice when it leaves that domain, for instance when an open highway turns into roadworks directed by a worker's hand signals, and fall back safely, calling on the driver if needed. Adaptive cruise control and lane centering count as Level 1; highway assist and automatic parking sit at Level 2.
Companies have chosen very different domains. Waymo became the first to offer driverless taxi rides in 2020, confining its service to city streets such as those of Phoenix and San Francisco. Tesla lets its Full Self-Driving feature run anywhere but only as a hands-on, eyes-on Level 2 system, and has acknowledged it does not handle every task on its own. Mercedes-Benz offered Level 3 in highway jams at up to 40 miles per hour before withdrawing it in January 2026, while Ford's BlueCruise covers 130,000 miles of American divided highways.
Marketing adds confusion. Britain's insurers called the word autonomous dangerous in adverts, because drivers may assume the car can look after itself. Trust remains limited: a 2022 survey found only 27 percent of people worldwide would feel safe riding in one, and as of late 2025 no system had reached full Level 5 autonomy.
Source: Self-driving car
