INTERNATIONAL ISO/SAE
STANDARD 22736
First edition
Taxonomy and definitions for terms
related to driving automation systems
for on-road motor vehicles
Taxonomie et définitions des termes relatifs aux systèmes de conduite
automatisée des véhicules routiers à moteur
PROOF/ÉPREUVE
Reference number
ISO/SAE 22736:2021(E)
ISO/SAE International 2021
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ISO/SAE 22736:2021(E)
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ISO/SAE 22736:2021(E)
Foreword

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This document was jointly prepared by Technical Committee ISO/TC 204, Intelligent transport systems,

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© ISO/SAE International 2021 – All rights reserved iii
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ISO/SAE 22736:2021(E)
TABLE OF CONTENTS

1. SCOPE ...................................................................................................................................... 1

2. REFERENCES .......................................................................................................................... 2

2.1 Applicable Documents ............................................................................................................... 2

2.1.1 SAE Publications ....................................................................................................................... 2

2.1.2 ANSI Accredited Publications .................................................................................................... 2

2.1.3 Other Publications ..................................................................................................................... 2

2.2 List of Abbreviations .................................................................................................................. 2

3. DEFINITIONS ............................................................................................................................ 3

4. TAXONOMY OF DRIVING AUTOMATION ............................................................................. 22

5. LEVELS OR CATEGORIES OF DRIVING AUTOMATION ..................................................... 28

5.1 Level or Category 0 - No Driving Automation .......................................................................... 28

5.2 Level or Category 1 - Driver Assistance .................................................................................. 28

5.3 Level or Category 2 - Partial Driving Automation .................................................................... 29

5.4 Level or Category 3 - Conditional Driving Automation............................................................. 29

5.5 Level or Category 4 - High Driving Automation ....................................................................... 29

5.6 Level or Category 5 - Full Driving Automation ......................................................................... 30

6. SIGNIFICANCE OF OPERATIONAL DESIGN DOMAIN (ODD) ............................................. 31

7. DEPRECATED TERMS ........................................................................................................... 32

7.1 Autonomous, Driving Modes(s), Self-Driving, Unmanned, Robotic ......................................... 33

7.1.1 Autonomous ............................................................................................................................. 33

7.1.2 Driving Mode(s)........................................................................................................................ 33

7.1.3 Self-Driving .............................................................................................................................. 33

7.1.4 Unmanned ............................................................................................................................... 33

7.1.5 Robotic ..................................................................................................................................... 33

7.2 Automated or Autonomous Vehicle ......................................................................................... 34

7.3 Control ..................................................................................................................................... 34

8. ADDITIONAL DISCUSSION .................................................................................................... 34

9. NOTES ..................................................................................................................................... 40

Figure 1 Examples of driving automation system features/types that could be available during a given

trip .............................................................................................................................................. 6

Figure 2 Schematic (not a control diagram) view of driving task showing DDT portion .......................... 7

Figure 3 ................................................................................................................................................... 9

Figure 4 ................................................................................................................................................... 9

Figure 5 ................................................................................................................................................. 10

Figure 6 ................................................................................................................................................. 10

Figure 7 ................................................................................................................................................. 10

Figure 8 ................................................................................................................................................. 11

Figure 9 Diagram showing vehicle axes of motion (SAE J670) ............................................................. 12

Figure 10 Simplified logic flow diagram for assigning driving automation level to a feature ................... 25

Figure 11 ODD relative to driving automation levels ............................................................................... 32

Figure 12 ODD relative to driving automation levels ............................................................................... 32

Figure 13 Use case sequence for a Level 3 feature showing ADS engaged, occurrence of a failure or

out-of-ODD condition, and the fallback-ready user performing the fallback, or, if the fallback-

ready user fails to do so, a failure mitigation strategy, such as stop-in-lane ........................... 37

Figure 14 Use case sequence at Level 4 showing ADS engaged, a catastrophic event (e.g., complete

power failure) and the system achieving a minimal risk condition ........................................... 37

Table 1 Summary of levels of driving automation ................................................................................. 23

Table 2 Roles of human user and driving automation system by level of driving automation .............. 26

Table 3 User roles while a driving automation system is engaged ...................................................... 28

iv © ISO/SAE International 2021 – All rights reserved
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INTERNATIONAL STANDARD ISO/SAE 22736:2021(E)
Taxonomy and Definitions for Terms Related to Driving
Automation Systems for On-Road Motor Vehicles
1. SCOPE

This document describes [motor] vehicle driving automation systems that perform part or all of the dynamic

driving task (DDT) on a sustained basis. It provides a taxonomy with detailed definitions for six levels of driving

automation, ranging from no driving automation (Level 0) to full driving automation (Level 5), in the context of

[motor] vehicles (hereafter also referred to as “vehicle” or “vehicles”) and their operation on roadways:

Level 0: No Driving Automation
Level 1: Driver Assistance
Level 2: Partial Driving Automation
Level 3: Conditional Driving Automation
Level 4: High Driving Automation
Level 5: Full Driving Automation

These level definitions, along with additional supporting terms and definitions provided herein, can be used to

describe the full range of driving automation features equipped on [motor] vehicles in a functionally consistent

and coherent manner. “On-road” refers to publicly accessible roadways (including parking areas and private

campuses that permit public access) that collectively serve all road users, including cyclists, pedestrians, and

users of vehicles with and without driving automation features.

The levels apply to the driving automation feature(s) that are engaged in any given instance of on-road operation

of an equipped vehicle. As such, although a given vehicle may be equipped with a driving automation system

that is capable of delivering multiple driving automation features that perform at different levels, the level of

driving automation exhibited in any given instance is determined by the feature(s) that are engaged.

This document also refers to three primary actors in driving: the (human) user, the driving automation system,

and other vehicle systems and components. These other vehicle systems and components (or the vehicle in

general terms) do not include the driving automation system in this model, even though as a practical matter a

driving automation system may actually share hardware and software components with other vehicle systems,

such as a processing module(s) or operating code.

The levels of driving automation are defined by reference to the specific role played by each of the three primary

actors in performance of the DDT and/or DDT fallback. “Role” in this context refers to the expected role of a

given primary actor, based on the design of the driving automation system in question and not necessarily to

the actual performance of a given primary actor. For example, a driver who fails to monitor the roadway during

engagement of a Level 1 adaptive cruise control (ACC) system still has the role of driver, even while s/he is

neglecting it.

Active safety systems, such as electronic stability control (ESC) and automatic emergency braking (AEB), and

certain types of driver assistance systems, such as lane keeping assistance (LKA), are excluded from the scope

of this driving automation taxonomy because they do not perform part or all of the DDT on a sustained basis,

but rather provide momentary intervention during potentially hazardous situations. Due to the momentary nature

of the actions of active safety systems, their intervention does not change or eliminate the role of the driver in

performing part or all of the DDT, and thus are not considered to be driving automation, even though they

perform automated functions. In addition, systems that inform, alert, or warn the driver about hazards in the

driving environment are also outside the scope of this driving automation taxonomy, as they neither automate

part or all of the DDT, nor change the driver’s role in performance of the DDT (see 8.13).

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ISO/SAE 22736:2021(E)

It should be noted, however, that crash avoidance features, including intervention-type active safety systems,

may be included in vehicles equipped with driving automation systems at any level. For automated driving

system (ADS) features (i.e., Levels 3 to 5) that perform the complete DDT, crash mitigation and avoidance

capability is part of ADS functionality (see also 8.13).
2. REFERENCES
2.1 Applicable Documents

The following publications form a part of this specification to the extent specified herein. Unless otherwise

indicated, the latest issue of SAE publications shall apply.
2.1.1 SAE Publications

Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323

(inside USA and Canada) or +1 724-776-4970 (outside USA), www.sae.org.
SAE J670 Vehicle Dynamics Terminology
SAE J3063 Active Safety Systems Terms and Definitions

Shi, E., Gasser, T., Seeck, A., and Auerswald, R., “The Principles of Operation Framework: A Comprehensive

Classification Concept for Automated Driving Functions,” SAE Intl. J CAV 3(1):27-37, 2020,

https://doi.org/10.4271/12-03-01-0003.
2.1.2 ANSI Accredited Publications
Copies of these documents are available online at http://webstore.ansi.org/.
ANSI D16.1-2007 Manual on Classification of Motor Vehicle Traffic Accidents
2.1.3 Other Publications
49 U.S.C. § 30102(a)(6) (definition of [motor] vehicle)

Crash Avoidance Metrics Partnership - Automated Vehicle Research Consortium, “Automated Vehicle

Research for Enhanced Safety - Final Report,” available at https://www.regulations.gov/document?D=NHTSA-

2014-0070-0003.

Gasser, T. et al., “Legal Consequences of an Increase in Vehicle Automation,” July 23, 2013, available at

http://bast.opus.hbz-

nrw.de/volltexte/2013/723/pdf/Legal_consequences_of_an_increase_in_vehicle_automation.pdf.

Michon, J.A., 1985, “A Critical View of Driver Behavior Models: What Do We Know, What Should We Do?” In

Evans, L. and Schwing, R.C. (Eds.). Human behavior and traffic safety (pp. 485-520). New York: Plenum Press,

1985.

Smith, B.W., “Engineers and Lawyers Should Speak the Same Robot Language,” in ROBOT LAW (2015),

available at https://newlypossible.org.
2.2 List of Abbreviations
ACC Adaptive cruise control
ADAS Advanced driver assistance system
ADS Automated driving system
ADS-DV Automated driving system-dedicated vehicle
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ISO/SAE 22736:2021(E)
AEB Automatic emergency braking
DDT Dynamic driving task
DSRC Dedicated short range communications
ESC Electronic stability control
LKA Lane keeping assistance
ODD Operational design domain
OEDR Object and event detection and response
3. DEFINITIONS
3.1 ACTIVE SAFETY SYSTEM (SAE J3063)

Active safety systems are vehicle systems that sense and monitor conditions inside and outside the vehicle for

the purpose of identifying perceived present and potential dangers to the vehicle, occupants, and/or other road

users, and automatically intervene to help avoid or mitigate potential collisions via various methods, including

alerts to the driver, vehicle system adjustments, and/or active control of the vehicle subsystems (brakes, throttle,

suspension, etc.).

NOTE: For purposes of this report, systems that meet the definition of active safety systems are considered to

have a design purpose that is primarily focused on improving safety rather than comfort, convenience,

or general driver assistance. Active safety systems warn or intervene during a high-risk event or

maneuver.
3.2 AUTOMATED DRIVING SYSTEM (ADS)

The hardware and software that are collectively capable of performing the entire DDT on a sustained basis,

regardless of whether it is limited to a specific operational design domain (ODD); this term is used specifically

to describe a Level 3, 4, or 5 driving automation system.

NOTE: In contrast to ADS, the generic term “driving automation system” (see 3.6) refers to any Level 1 to 5

system or feature that performs part or all of the DDT on a sustained basis. Given the similarity between

the generic term, “driving automation system,” and the Level 3 to 5 specific term, “automated driving

system,” the latter term should be capitalized when spelled out and reduced to its abbreviation, ADS,

as much as possible, while the former term should not be.
3.3 [DRIVERLESS OPERATION] DISPATCHING ENTITY
An entity that dispatches an ADS-equipped vehicle(s) in driverless operation.

NOTE: The functions carried out by a dispatching entity may be divided among one or several agents,

depending on the usage specification for the ADS-equipped vehicle(s) in question.

EXAMPLE: A fleet of Level 4 closed campus ADS-dedicated vehicles is placed into service by a driverless

operation dispatching entity, which engages the ADS for each vehicle after verifying its operational

readiness and disengages the ADS when each vehicle is taken out of service.
3.4 DISPATCH [IN DRIVERLESS OPERATION]

To place an ADS-equipped vehicle into service in driverless operation by engaging the ADS.

NOTE 1: The term “dispatch,” as used outside of the context of ADS-equipped vehicles, is generally understood

to mean sending a particular vehicle to a particular pick-up or drop-off location for purposes of

providing a transportation service. In the context of ADS-equipped vehicles, and as used herein, this

term includes software-enabled dispatch of multiple ADS-equipped vehicles in driverless operation

that may complete multiple trips involving pick-up and drop-off of passengers or goods throughout a

day or other pre-defined period of service, and which may involve multiple agents performing various

tasks related to the dispatch function. In order to highlight this specialized use of the term dispatch,

the term is modified and conditioned by the stipulation that it refers exclusively to dispatching vehicles

in driverless operation.

NOTE 2: Only ADS-equipped vehicles capable of driverless operation (namely, an ADS-DV or a dual-mode

vehicle) are potentially subject to being dispatched.
3.5 DRIVING AUTOMATION

The performance by hardware/software systems of part or all of the DDT on a sustained basis.

3.6 DRIVING AUTOMATION SYSTEM OR TECHNOLOGY

The hardware and software that are collectively capable of performing part or all of the DDT on a sustained

basis; this term is used generically to describe any system capable of Level 1 to 5 driving automation.

NOTE: In contrast to this generic term for any Level 1 to 5 system, the specific term for a Level 3 to 5 system

is “automated driving system (ADS).” Given the similarity between the generic term, “driving automation

system,” and the Level 3 to 5 specific term, “Automated Driving System,” the latter term should be

capitalized when spelled out and reduced to its abbreviation, ADS, as much as possible, while the

former term should not be (see 3.2).
3.7 [DRIVING AUTOMATION SYSTEM] FEATURE

A Level 1-5 driving automation system’s design-specific functionality at a given level of driving automation within

a particular ODD, if applicable.

NOTE 1: Because the term “driving automation system” subsumes both driver support features and ADS

features, it is also acceptable to refer to them as such.

NOTE 2: A given driving automation system may have multiple features, each associated with a particular level

of driving automation and ODD.
NOTE 3: Each feature satisfies a usage specification.

NOTE 4: Features may be referred to by generic names (e.g., automated parking) or by proprietary names.

EXAMPLE 1: A Level 3 ADS feature that performs the DDT, excluding DDT fallback, in high-volume traffic on

fully access-controlled freeways.

EXAMPLE 2: A Level 4 ADS feature that performs the DDT, including DDT fallback, in a specified geo-fenced

A driving automation system feature equipped on a conventional vehicle that either:

1. Supports the driver by executing a limited set of lateral and/or longitudinal vehicle motion control actions

sufficient to fulfil a specific, narrowly defined use case (e.g., parking maneuver), while the driver performs

the rest of the DDT and supervises the Level 1 or Level 2 feature’s performance (i.e., Level 1 or Level 2

driver support features);
or

2. Executes a limited set of lateral and longitudinal vehicle motion control actions, as well as associated object

and event detection and response (OEDR) and all other elements of the complete DDT in order to fulfil a

specific, narrowly defined use case without human supervision (Level 3 or 4 ADS features).

EXAMPLE 1: A Level 1 parking assistance feature automatically performs the lateral vehicle motion control

actions necessary to parallel park a vehicle, while the driver performs the longitudinal vehicle

motion control actions and supervises the feature.

EXAMPLE 2: A Level 2 parking assistance feature automatically performs the lateral and longitudinal vehicle

motion control actions necessary to parallel park a vehicle under the supervision of the driver.

EXAMPLE 3: A Level 3 highway overtaking assistance feature automatically performs the lateral and

longitudinal vehicle motion control actions, as well as associated OEDR, necessary to pass a

slower-moving vehicle on a multi-lane highway when activated by the driver or fallback-ready

user.
3.7.2 SUB-TRIP FEATURE

A driving automation system feature equipped on a conventional vehicle that requires a human driver to perform

the complete DDT for at least part of every trip.

NOTE: Sub-trip features require a human driver to operate the vehicle between the point-of-origin and the

boundary of the feature’s ODD and/or after leaving the feature’s ODD until the destination is reached

(i.e., trip completion).

EXAMPLE 1: A Level 1 adaptive cruise control (ACC) feature performs longitudinal vehicle motion control

functions to support the driver in maintaining consistent headway to a lead vehicle in its lane when

travelling at higher speeds.

EXAMPLE 2: A Level 2 highway feature performs lateral and longitudinal vehicle motion control functions to

support the driver in maintaining position within its lane of travel, as well as consistent headway

to a lead vehicle in its lane when travelling at higher speeds.

EXAMPLE 3: A Level 3 traffic jam feature performs the complete DDT on a fully access-controlled freeway in

dense traffic, but requires a human driver to operate the vehicle upon ODD exit (e.g., when traffic

clears, as well as before entering the congested freeway, and again upon exiting it).

EXAMPLE 4: During a given vehicle trip, a user with a Level 4 automated parking feature dispatches the vehicle

in driverless operation for the purpose of finding a parking space in a nearby designated parking

facility. Following a period of shopping, the user retrieves the vehicle via dispatch in order to begin

his/her trip home.
3.7.3 FULL-TRIP FEATURE
ADS features that operate a vehicle throughout complete trips.

EXAMPLE 1: A Level 4 ADS-DV is dispatched in driverless operation for purposes of providing ride-hailing

EXAMPLE 2: A Level 5 dual-mode vehicle is dispatched in driverless operation by its owner to go to a

designated airport, pick up several family members, and bring them home. All vehicle occupants

remain passengers throughout the return trip.

Figure 1 illustrates how a trip could be completed by use of various combinations of driving automation features

engaged at different levels of driving automation.

Figure 1 — Examples of driving automation system features/types that could be available during a

given trip
3.8 DRIVER SUPPORT [DRIVING AUTOMATION SYSTEM] FEATURE
A general term for Level 1 and Level 2 driving automation system features.

NOTE: Level 1 (driver assistance) and Level 2 (partial automation) features are capable of performing only part

of the DDT, and thus require a driver to perform the remainder of the DDT, as well as to supervise the

feature’s performance while engaged. As such, these features, when engaged, support—but do not

replace—a driver in performing the DDT.
3.9 DRIVERLESS OPERATION [OF AN ADS-EQUIPPED VEHICLE]

On-road operation of an ADS-equipped vehicle that is unoccupied, or in which on-board users are not drivers

or in-vehicle fallback-ready users.

NOTE 1: ADS-DVs are always dispatched in driverless operation (subject to NOTE 3 in 3.33.3).

NOTE 2: ADS-equipped dual-mode vehicles may be dispatched in driverless operation.

NOTE 3: On-board passengers are neither drivers nor fallback-ready users.

EXAMPLE: A Level 4 ADS-DV is dispatched in driverless operation for purposes of providing transportation

service.
3.10 DYNAMIC DRIVING TASK (DDT)

All of the real-time operational and tactical functions required to operate a vehicle in on-road traffic, excluding

the strategic functions such as trip scheduling and selection of destinations and waypoints, and including,

without limitation, the following subtasks:
6 © ISO/SAE International 2021 – All rights reserved
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ISO/SAE 22736:2021(E)
1. Lateral vehicle motion control via steering (operational).

2. Longitudinal vehicle motion control via acceleration and deceleration (operational).

3. Monitoring the driving environment
...

ISO/SAE PRF PAS 22736

Taxonomy and definitions for terms related to driving automation systems for on-road motor vehicles

Taxonomy and definitions for terms related to driving automation systems for on-road motor vehicles

Taxonomie et définitions des termes relatifs aux systèmes de conduite automatisée des véhicules routiers à moteur

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Taxonomy and definitions for terms related to driving automation systems for on-road motor vehicles

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