
control and driver intervention. One such classification has been suggested for the United States by the
National Highway Traffic Safety Administration (NHTSA) and is as follows:
• Level 0—the driver completely controls the vehicle at all times.
• Level 1—individual vehicle controls are automated, such as electronic stability control or
automatic braking.
• Level 2—at least two controls can be automated in unison, such as adaptive cruise control (ACC) in
combination with lane keeping.
• Level 3—the driver can fully cede control of all safety-critical functions in certain conditions. The
car senses when conditions require the driver to retake control and provides a “sufficiently
comfortable transition time” for the driver to do so.
• Level 4—the vehicle performs all safety-critical functions for the entire trip, with the driver not
expected to control the vehicle at any time. As this vehicle would control all functions from start to
stop, including all parking functions, it could include unoccupied cars.
The SAE is an important organization that has consistently promoted new automotive technology. It
also forms groups of engineers, technicians, and legal experts for creating and publishing standards and
recommended practices. This organization has presented a classification system for autonomous ve-
hicles that has six levels, depending on the level of human driver intervention and environmental ob-
servations and supervisory decision-making. These six levels of classification are the following:
• Level 0—automated system has no vehicle control but may issue warnings.
• Level 1—driver must be ready to take control at anytime. Auto mated system may include features
such as ACC, parking assistance with automated steering, and lane keeping assistance (LKA) type
II in any combination.
• Level 2—the driver is obliged to detect objects and events and respond if the automated system fails
to respond properly. The automated system executes accelerating, braking, and steering. The
automated system can deactivate immediately on takeover by the driver.
• Lever 3—within known, limited environments (such as freeways), the driver can safely turn their
attention away from driving tasks.
• Level 4—the automated system can control the vehicle in all but a few environments such as severe
weather. The driver must enable the automated system only when it is safe to do so. When enabled,
driver attention is not required.
• Level 5—other than setting the destination and starting the system, no human intervention is
required. The automatic system can drive to any location where it is legal to drive.
It is important to note that essentially all of the electronic subsystem hardware and control software
necessary to implement an autonomous vehicle at any of the above levels exists as of the time of this
writing. The major development required for the higher levels listed above is the algorithms required
to process sensor data, make decisions, and regulate the various subsys tems. However, before proceed-
ing with a discussion of this software aspect of autonomous vehicles, it is necessary to explain the
one electronic subsys tem that has not been discussed elsew here in this book. That subsystem is auto-
matic steering. Such a system exists in certain production vehicles at the time of this writing and is an
automatic parallel parking system (APPS), which is presented next. The main feature of APPS as it
relates to autonomous vehicles is computer-controlled automatic steering of the vehicle.
574 CHAPTER 12 AUTONOMOUS VEHICLES
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