190 PART | V The future of ITS applications
• Finally, in the “Full Automation” level, the system takes full control of the
vehicle. If a takeover request is rejected by the driver (or fails), the system
returns to the minimal risk condition by itself.
They also refer to the degree of automation that can be warning only, control
assistance or full automation and the degree of autonomy or cooperation with
the driver, which defines a canvas for the various autonomous driving enablers
and approaches.
In a similar manner, the US National Highway Traffic Safety Administra-
tion defines five levels of automation and ranges from the complete absence
of automation (Level 0) to vehicles at the full automation level (Level 4)
(NHTSA, 2013).
• Level 0, no automation: It is on the responsibility of the driver to moni-
tor the roadway at all times and operate all the vehicle navigation controls,
such as the wheel, the brake, and the throttle. Vehicles at this level may
have several driver assistance/convenience systems (e.g., collision warning
systems, blind-spot monitors, etc.), but do not have any control authority on
the aforementioned vehicle controls. All vehicles that contain only warning
technologies but do not take action are classified at this level.
• Level 1, function-specific automation: In this level, the driver still has the
overall control, and is responsible for operating the vehicle, but has the op-
tion to activate specific control functions, which are automated, but oper-
ate independently. Examples of such control functions are adaptive cruise
control, crash avoidance (e.g., by dynamic braking), or lane-keeping (e.g.,
by automatic steering) technologies. They may assist the driver in operating
one vehicle control at a time without replacing the driver.
• Level 2, combined function automation: The combined automatic opera-
tion of two or more control functions is the main characteristic of this level.
The responsibility of roadway monitoring remains at the driver, who has
control of the vehicle at all times. However, in a few cases, the vehicle gets
the control of the main navigation controls (gas, brake, wheel) and this is
done when the driver decides to delegate such authority to the vehicle. For
example, when the driver takes his/her hands off the steering wheel and the
foot off the pedal at the same time, this can trigger in tandem the operation
of the adaptive cruise control and the lane-keeping system.
• Level 3, limited self-driving automation: This level assumes that the vehicle
gets full control of all functions that are safety-critical and this is allowed
only under specific traffic and environmental conditions. In addition, the
driver must be ready to take control back when the conditions change. The
transition time must be adequate for the driver (who constantly monitors
the roadway) to safely take control of the vehicle, so it is important to early
notify the driver. For example, a self-driving car of this level can take full
control while on the highway but early notifies the driver when a sign for
road construction works appears.