The autonomy of cars is defined by six levels in the SAE standard J3016. SAE’s levels range from zero autonomy, where the car is operated solely by its human driver, to full autonomy, where the car is operating independent from human input.
Level 0 – No autonomy
A level 0 car will not assist by taking over a part of the driving functionality. It is limited to warn the driver about e. g. dangerous situations but the reaction has to be done by the driver. The lane departure warning would be an example for a level 0 system. It warns by vibrating the steering wheel, if the car crosses the right or left lane markings without an activated blinker.
Level 1 – One domain autonomy
Systems like adaptive cruise control or lane keeping assists are enabling level 1. It means that a single domain like the lateral or longitudinal control is done by an assistance system. The other is controlled by the driver.
The adaptive cruise control keeps the longitudinal control of the car. It accelerates or brakes based on the distance to the car in the front. The lane keeping assist controls the lateral position of the car based on the relative position to the lane markings.
Level 2 – Two domain autonomy
Level 2 means that both driving functions are controlled by the car. Lateral and longitudinal control is done by the cars built-in systems. Activating adaptive cruise control and lane keeping assistant at the same time means already level 2.
Level 3 – Pushing driving responsibility to the car built-in systems
The levels 0 to 2 have always the requirement that the driver holds the full responsibility to the driving behavior and should be able to take over the driving control at any time.
Level 3 moves this responsibility to the piloted driving system of the car. The driver is allowed to be inattentive to driving and can focus on other tasks. The response time to take over the driving task should be within ten seconds.
Level 4 – No driver interaction in predefined scenarios
For the level 4 of autonomous driving no driver interaction is needed within specific scenarios. This means that the car can drive fully autonomously on certain roads. For example a level 4 highway pilot system can run without a driver between the entry and exit of the highway. The driver can even sleep during this part of the drive.
Level 5 – No driver needed at all
The last level (level 5) means the driver is not needed in any case or in any scenario of driving. No steering wheel or brake pedal is needed anymore. The driver is only a passenger during the whole drive.
This was way to much text, and you just need a quick graphical overview? Here you go!