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SAE/NHTSA Levels

In the earliest days of regulatory effort, NHTSA defined 4 “levels” for self-driving vehicles, plus a “level 0” to refer to classic manually driven vehicles. Later, the SAE expanded this to 5 levels by splitting the 4th level into two forms. Initially the levels were presented as that – a progression of technology, but later statements were added to indicate that the numbers were not necessary an ordering, and in fact the first commercial products were shuttles that matched level 4.

The initial NHTSA levels focused on the role of a human supervisor in the vehicle.

  1. Typical ADAS such as automatic emergency braking, lane departure warnings, ABS, ESC etc.
  2. The combination of ADAS functions, in particular adaptive cruise control and lanekeeping to allow a car to be driven without human operation of the controls, but which still required a human supervisor to be watching the road at all times, ready to take over.
  3. A car capable of operation without full time supervision, but which might encounter situations where supervision would be needed with reasonable advance warning. The human must be in a driver's seat on standby, ready to take control on about 10-20 seconds notice, but can do things like read.
  4. A car capable of operation with no human at all

SAE adapted level 4 to split between a car that could do that on a specific set of roads or under certain conditions, and level 5, which was a car that could operate with no human on all roads and in all conditions. The set of roads and conditions a car at level 3 or 4 could operate without a human was termed the Operational Design Domain (ODD.)

Level 5 is a somewhat science-fictional goal, Nobody has serious sight of it, and it is speculated this requires human level intelligence, or if not, involves certifying cars for all sorts of rarely driven roads and conditions that may not be commercially viable for a long time. Level 3 is just level 4 when the car drives in a way that it must leave its ODD at speed.

As such, level 4 is the only meaningful one, and the real question is not what role the human being plays but what the ODD is for the vehicle. In spite of this, people frequently talk about these levels.