The biggest dividing line is responsibility. At Levels 0–2, the human driver remains responsible for monitoring the road. At Levels 3–5, the automated driving system performs the complete dynamic driving task when engaged, with different fallback and operating-domain requirements.
Levels 0–5
| Level | Plain-language meaning | Human role |
|---|---|---|
| 0 | Warnings or momentary assistance | Driver drives and monitors |
| 1 | Continuous assistance with steering OR speed control | Driver drives and monitors |
| 2 | Continuous assistance with steering AND speed control | Driver still monitors the road and remains responsible |
| 3 | Conditional automation | System drives; human must be available to respond to a takeover request |
| 4 | High automation within an ODD | System drives and handles fallback inside its operating domain; human driver not required there |
| 5 | Full automation everywhere a human can drive | No human driver required |
Why Level 2 is often misunderstood
Modern Level 2 systems can steer, accelerate and brake for long periods, making the car feel highly automated. But NHTSA’s consumer guidance is explicit: the driver remains responsible and must stay engaged and attentive.
Level 3 vs Level 4
At Level 3, the system performs the driving task while engaged but can require the human to take over. At Level 4, the system must be able to manage the driving task and fallback within its operational design domain without relying on a human driver.
Do the levels describe the whole car?
No. A vehicle may contain multiple driving features with different capabilities and operating conditions. The level applies to the driving automation feature, not as a universal badge for every situation the vehicle encounters.