Classification
A classification system based on six different levels (ranging from
fully manual to fully automated systems) was published in 2014 by SAE
International, an automotive standardization body, as J3016, Taxonomy
and Definitions for Terms Related to On-Road Motor Vehicle Automated
Driving Systems. This classification system is based on the amount of
driver intervention and attentiveness required, rather than the vehicle
capabilities, although these are very loosely related. In the United
States in 2013, the National Highway Traffic Safety Administration
(NHTSA) released a formal classification system, but abandoned this
system in favor of the SAE standard in 2016. Also in 2016, SAE updated
its classification, called J3016_201609.
Levels of driving automation
In SAE’s automation level definitions, “driving mode” means “a type
of driving scenario with characteristic dynamic driving task
requirements (e.g., expressway merging, high speed cruising, low speed
traffic jam, closed-campus operations, etc.)”
Level 0: Automated system issues warnings and may momentarily intervene
but has no sustained vehicle control.
Level 1 (“hands on”): The driver and the automated system share
control of the vehicle. Examples are Adaptive Cruise Control (ACC),
where the driver controls steering and the automated system controls
speed; and Parking Assistance, where steering is automated while speed
is under manual control. The driver must be ready to retake full control
at any time. Lane Keeping Assistance (LKA) Type II is a further example
of level 1 self-driving.
Level 2 (“hands off”): The automated system takes full control of the
vehicle (accelerating, braking, and steering). The driver must monitor
the driving and be prepared to intervene immediately at any time if the
automated system fails to respond properly. The shorthand “hands off”
is not meant to be taken literally. In fact, contact between hand and
wheel is often mandatory during SAE 2 driving, to confirm that the
driver is ready to intervene.
Level 3 (“eyes off”): The driver can safely turn their attention away
from the driving tasks, e.g. the driver can text or watch a movie. The
vehicle will handle situations that call for an immediate response, like
emergency braking. The driver must still be prepared to intervene within
some limited time, specified by the manufacturer, when called upon by
the vehicle to do so. As an example, the 2018 Audi A8 Luxury Sedan was
the first commercial car to claim to be capable of level 3 self-driving.
This particular car has a so-called Traffic Jam Pilot. When activated by
the human driver, the car takes full control of all aspects of driving
in slow-moving traffic at up to 60 kilometers per hour (37 mph). The
function works only on highways with a physical barrier separating one
stream of traffic from oncoming traffic.
Level 4 (“mind off”): As level 3, but no driver attention is ever
required for safety, i.e. the driver may safely go to sleep or leave the
driver’s seat. Self-driving is supported only in limited spatial areas
(geofenced) or under special circumstances, like traffic jams. Outside
of these areas or circumstances, the vehicle must be able to safely
abort the trip, i.e. park the car, if the driver does not retake
control.
Level 5 (“steering wheel optional”): No human intervention is required
at all. An example would be a robotic taxi.
In the formal SAE definition below, note in particular what happens in
the shift from SAE 2 to SAE 3: the human driver no longer has to monitor
the environment. This is the final aspect of the “dynamic driving
task” that is now passed over from the human to the automated system.
At SAE 3, the human driver still has the responsibility to intervene
when asked to do so by the automated system. At SAE 4 the human driver
is relieved of that responsibility and at SAE 5 the automated system
will never need to ask for an intervention.