The Society of Automotive Engineers defines 6 levels of autonomous vehicles zero through five.
Level Zero :-
This is the basic level at these level ,the driver is the sole decision maker of the system,the driver controls the steering wheel,throttle brakes and all other vehicle controls.
Level One :-
Level one is driver assistance i.e Driver fully engaged ,at this level the vehicle supports the driver with either steering or acceleration.Cruise control,for example is a level one automation system.At this level drivers must stay fully engaged but they can give up some contol to the autonomous system.
Level Two is partial automation at this stage vehicle controls several functions automatically such as automatic cruise control and lane keeping,however driver must still perform any function that the autonomous system does not handle.
Level Three :-
It is conditional automation in these vehicle drives autonomously but the driver must be ready to take over whenever necessary.
It is high automation i.e no human interference at this level the vehicle controls all aspects of driving experience and there is no expectation that the human driver will ever intervene.In this level its possible that the vehicle might not even have a steering wheel or driver controls at all,However at this level the vehicle may be restricted to certain areas ,often this is called geofence.The vehicle can operate completely autonomously within a certain geofence but outside of the geofence the vehicle is either unable to operate autonomously or maybe unable to operate at all.
It is the highest level i.e full automation, at this level vehicle operates completely autonomously anywhere and everywhere that a human can drive.It should be automation as good or better than a human driver in all scenarios.