ETSI TR 103 299 V2.1.1 (2019-06)

TECHNICAL REPORT
Intelligent Transport Systems (ITS);
Cooperative Adaptive Cruise Control (CACC);
Pre-standardization study
2 ETSI TR 103 299 V2.1.1 (2019-06)

Reference
DTR/ITS-00164
Keywords
autonomic networking, ITS
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3 ETSI TR 103 299 V2.1.1 (2019-06)
Contents
Intellectual Property Rights . 6
Foreword . 6
Modal verbs terminology . 6
Introduction . 6
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 7
3 Definition of terms, symbols and abbreviations . 8
3.1 Terms . 8
3.2 Symbols . 9
3.3 Abbreviations . 9
4 CACC introduction . 10
4.1 Background . 10
4.2 CACC definition . 11
4.3 CACC target time gap . 11
4.4 CACC and automation levels . 12
5 CACC use cases and operations . 13
5.1 UC001: Follow the TV at configured Δt . 13
target
5.1.1 Introduction. 13
5.1.2 Pre-conditions . 13
5.1.3 Actors . 13
5.1.4 Triggering condition . 13
5.1.5 Normal Flow . 13
5.1.6 Termination condition. 14
5.1.7 Use case diagram and use case illustration . 14
5.1.8 Alternative flow . 15
5.1.9 Post-conditions . 16
5.2 UC002: Follow the TV at automatically adjusted Δt . 16
target
5.2.1 Introduction. 16
5.2.2 Pre-conditions . 16
5.2.3 Actors . 16
5.2.4 Triggering condition . 16
5.2.5 Termination condition. 17
5.2.6 Use case diagram and use case illustration . 17
5.2.7 Normal Flow . 18
5.2.8 Alternative flow . 18
5.2.9 Post-conditions . 18
5.3 UC003: Single lane CACC string . 18
5.3.1 Introduction. 18
5.3.2 Pre-conditions . 18
5.3.3 Actors . 18
5.3.4 Triggering condition . 18
5.3.5 Termination condition. 19
5.3.6 Use case diagram and use case illustration . 19
5.3.7 Normal Flow . 19
5.3.8 Alternative flow . 19
5.3.9 Post-conditions . 20
5.4 UC004: Single lane CACC string support service provided by road side . 20
5.4.1 Introduction. 20
5.4.2 Pre-conditions . 20
5.4.3 Actors . 20
5.4.4 Triggering condition . 21
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4 ETSI TR 103 299 V2.1.1 (2019-06)
5.4.5 Termination condition. 21
5.4.6 Use case diagram and use case illustration . 21
5.4.7 Normal Flow . 21
5.4.8 Alternative flow . 22
5.4.9 Post-conditions . 22
5.5 UC005: Co-operation of lane keeping assistance system and CACC . 22
5.5.1 Introduction. 22
5.5.2 Pre-conditions . 22
5.5.3 Actors . 22
5.5.4 Triggering condition . 22
5.5.5 Termination condition. 22
5.5.6 Normal Flow . 22
5.5.7 Alternative flow . 23
5.5.8 Post-conditions . 23
5.6 UC006: Co-operation of lane change assistance system and CACC . 23
5.6.1 Introduction. 23
5.6.2 Pre-conditions . 23
5.6.3 Actors . 23
5.6.4 Triggering condition . 23
5.6.5 Termination condition. 24
5.6.6 Normal Flow . 24
5.6.7 Alternative flow . 24
5.6.8 Post-conditions . 24
5.7 UC007: CACC pair passing through I2V equipped traffic lights . 24
5.7.1 Introduction. 24
5.7.2 Pre-conditions . 24
5.7.3 Actors . 24
5.7.4 Triggering condition . 25
5.7.5 Termination condition. 25
5.7.6 Use case diagram and use case illustration . 25
5.7.7 Normal Flow . 25
5.7.8 Alternative flow . 25
5.7.9 Post-conditions . 26
6 CACC architecture . 26
6.1 Functional architecture . 26
6.2 Information architecture . 27
6.3 Communication architecture . 28
7 Functional requirements . 30
7.1 Application layer . 30
7.2 Facilities layer . 30
7.3 Networking & Transport layer . 30
7.4 Access layer . 31
7.5 Management & security . 31
8 Operational requirements . 31
8.1 Application layer . 31
8.2 Facilities layer . 31
8.3 Networking & Transport layer . 32
8.4 Access layer . 32
9 Standards recommendations . 32
9.1 Facilities layer . 32
9.1.1 Options for CACC data inclusion in facilities layer PDU . 32
9.1.2 CA basic service . 32
9.1.2.1 Introduction . 32
9.1.2.2 Triggering conditions . 33
9.1.2.3 Message content extension . 33
9.1.2.4 Dissemination requirements . 33
9.1.2.5 Dissemination protocol . 33
9.1.2.6 Security requirements. 34
9.1.2.6.1 ITS AID management . 34
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5 ETSI TR 103 299 V2.1.1 (2019-06)
9.1.2.6.2 SSP . 34
9.2 Networking & Transport layer . 34
9.3 Access layer . 34
9.3.1 Channel usage . 34
9.3.2 Over-the-air update . 35
9.4 Management & security . 35
9.4.1 Communication profile and SAM . 35
9.4.2 Security and privacy . 35
Annex A: Recommendations on CACC DEs and DFs . 36
A.1 DEs and DFs to support CACC use cases . 36
A.2 DE and DF data setting rules . 38
A.2.1 accelerationControl . 38
A.2.2 timeToPrecedingVehicle . 38
A.2.3 automatedVehicleContainerLowFrequency . 38
A.2.4 roadSideSupportedAutomatedDriving . 39
A.2.5 automatedConrtrol . 39
A.2.6 targetSpeed . 39
A.2.7 targetLongitudinalAcceleration . 39
A.2.8 brakingCapacity . 39
A.2.9 targetTimeToPrecedingVehicle . 39
A.2.10 targetTimeToFollowingVehicle . 40
A.2.11 pathPrediction . 40
A.2.12 groupID . 40
A.2.13 groupSpeed . 40
A.2.14 limitedLength . 40
A.2.15 stringLeadVehiclePosition . 40
A.2.16 limitedLengthInNumber . 41
A.2.17 orderInString . 41
A.2.18 leadVehicle . 41
A.2.19 roadSideCaccContainer . 41
A.2.20 recommendedTargetTimeGap . 41
A.2.21 startingPosition . 41
A.2.22 caccLanePosition . 41
A.2.23 recommendedSpeed. 42
A.2.24 recommendedVehicleType . 42
Annex B: Application state machine transition . 43
Annex C: Bibliography . 44
History . 45

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6 ETSI TR 103 299 V2.1.1 (2019-06)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Intelligent Transport Systems (ITS).
Modal verbs terminology
In the present document "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be
interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
The CACC application is an extension of the in-vehicle Adaptive Cruise Control (ACC) system. It enables further
reduction of the time gap with preceding vehicles compared to the ACC system, thanks to Vehicular communications.

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7 ETSI TR 103 299 V2.1.1 (2019-06)
1 Scope
The present document describes the outputs of a pre-standardization study of the Cooperative Adaptive Cruise Control
(CACC) application. It consists of:
• Definition of the CACC use cases;
• Definition of CACC architecture;
• Requirement analysis of the application and the communication systems;
• Recommendations on the standardization needs for the communication layers (including facilities layer,
Networking & Transport layer and access layer) in support of the CACC application;
• Recommendation on the CACC application standardization.
2 References
2.1 Normative references
Normative references are not applicable in the present document.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] "G7 declaration on automated and connected driving" (09/2015).
NOTE: Also available at https://ec.europa.eu/commission/commissioners/2014-2019/bulc/announcements/g7-
declaration-automated-and-connected-driving_en.
[i.2] ETSI EN 302 665 (V1.1.1): "Intelligent Transport Systems (ITS); Communications Architecture".
[i.3] SAE J3016: "Taxonomy and Definitions for Terms Related to On-Road Motor Vehicle Automated
Driving Systems".
[i.4] ETSI TS 101 539-3: "Intelligent Transport Systems (ITS); V2X Applications; Part 3: Longitudinal
Collision Risk Warning (LCRW) application requirements specification".
[i.5] ETSI TS 101 539-2: "Intelligent Transport Systems (ITS); V2X Applications; Part 2: Intersection
Collision Risk Warning (ICRW) application requirements specification".
[i.6] ETSI EN 302 637-2 (V1.4.1): "Intelligent Transport Systems (ITS); Vehicular Communications;
Basic Set of Applications; Part 2: Specification of Cooperative Awareness Basic Service".
[i.7] ETSI EN 302 637-3 (V1.3.1): "Intelligent Transport Systems (ITS); Vehicular Communications;
Basic Set of Applications; Part 3: Specifications of Decentralized Environmental Notification
Basic Service".
[i.8] ISO 15622: "Intelligent Transport Systems - Adaptive Cruise Control Systems (ACC) -
Performance requirements and test procedures".
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8 ETSI TR 103 299 V2.1.1 (2019-06)
[i.9] "Using Cooperative Adaptive Cruise Control (CACC) to Form High-Performance Vehicle
Streams; Definitions, Literature Review and Operational Concept Alternatives".
NOTE: Available at: https://escholarship.org/uc/item/3m89p611.
[i.10] ETSI TS 103 301 (V1.1.1): "Intelligent Transport Systems (ITS); Vehicular Communications;
Basic Set of Applications; Facilities layer protocols and communication requirements for
infrastructure services".
[i.11] ETSI TS 102 894-1 (V1.1.1): "Intelligent Transport Systems (ITS); Users and applications
requirements; Part 1: Facility layer structure, functional requirements and specifications".
[i.12] ISO/DIS/20035: "Intelligent Transport Systems - Cooperative Adaptive Cruise Control Systems
(CACC) - Performance requirements and test procedures".
[i.13] ETSI TS 102 894-2 (V1.3.1): "Intelligent Transport Systems (ITS); Users and applications
requirements; Part 2: Applications and facilities layer common data dictionary".
[i.14] Result of C-ITS Platform Phase II Release 1 (12/2017): "Security Policy & Governance
Framework for Deployment and Operation of European Cooperative Intelligent Transport Systems
(C-ITS)".
NOTE: Available at: https://ec.europa.eu/transport/sites/transport/files/c-its_security_policy_release_1.pdf.
[i.15] ETSI TS 103 097 (V1.3.1): "Intelligent Transport Systems (ITS); Security; Security header and
certificate formats".
[i.16] AUTONET 2030 D3.2: "Specifications for the enhancement to existing LDM and cooperative
communication protocol standards".
NOTE: Available at: http://www.autonet2030.eu/wp-content/uploads/2015/02/D3.2-Specifications-cooperative-
communication-protocol-standards-draft-for-approval.pdf.
[i.17] DATEX II release 3.0.
NOTE: Available at: https://datex2.eu/support/getting_started.
[i.18] OCIT®-C: "Open Communication Interface for Road Traffic Control Systems - Center to Center".
NOTE: Available at: https://www.ocit.org/en/ocit/interfaces/ocit-c/.
3 Definition of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the following terms apply:
active CACC vehicle: CACC vehicle with CACC at active state
CACC: V2X capable in-vehicle driving assistance system that adjusts automatically the vehicle speed to keep a target
time gap with target vehicle while keeping a minimum safety distance, making use of information communicated from
other vehicles and/or from the roadside infrastructure
CACC application: application layer entity that implements the CACC functionalities and application logic
CACC pair: subject vehicle and its target vehicle
CACC string: two or more CACC pairs in sequence
st nd
NOTE: 1 active CACC vehicle is the target vehicle of the 2 active CACC vehicle, and so forth.
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9 ETSI TR 103 299 V2.1.1 (2019-06)
CACC vehicle: vehicle equipped with the system in question
NOTE 1: A CACC vehicle may or may not activate CACC at a point in time.
NOTE 2: A CACC vehicle is V2X capable.
lead vehicle: first vehicle in the upstream end of CACC string or a CACC pair
NOTE 1: The lead vehicle may not be CACC vehicle.
NOTE 2: In a CACC pair, the lead vehicle and target vehicle may be identical.
st
NOTE 3: Lead vehicle of a CACC string is the target vehicle of the 1 active CACC vehicle.
measured time gap: time gap between a subject vehicle and its preceding vehicle, measured at one point in time
subject vehicle: CACC vehicle with the role to follow a target vehicle
target time gap: time gap targeted by the subject vehicle for CACC operation
target vehicle: V2X capable vehicle and counterpart of the subject vehicle for the CACC application
NOTE: The target vehicle is not necessarily a CACC vehicle.
time gap: time interval between when a preceding vehicle's rear end and a following vehicle's front end passes the same
location on the road surface, assuming that the following vehicle speed remains constant
V2X capable: capable of transmitting and/or receiving facilities and application layer message (e.g. CAM) with other
ITS-S using wireless communications
3.2 Symbols
For the purposes of the present document, the following symbols apply:
∆ Minimun safety time gap
v Instant speed of subject vehicle
s
v Instant speed of TV
t
a Maximum deceleration of SV
sv
Δt Target time gap
target
Δt Time gap between two vehicles
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ACC Adaptive Cruise Control
BTP Basic Transport Protocol
CA Cooperative Awareness
CACC Cooperative ACC
CAM Cooperative Awareness Message
CC Cruise Control
DATEX II DATa EXchange II
DATEX DATa EXchange standard for exchanging traffic information
DCC Decentralized Congestion Control
DE Data Element
DEN Decentralized Environmental Notification
DENM Decentralized Environmental Notification Message
DF Data Frame
GDPR General Data Protection Regulation
GN GeoNetworking
GN/BTP GeoNetworking/Basic Transport Prototol
HMI Human Machine Interface
HW/SW Hardware/Software
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10 ETSI TR 103 299 V2.1.1 (2019-06)
I2V Infrastructure to Vehicle
ITS Intelligent Transport System
ITS-S ITS Station
LDM Local Dynamic Map
MAPEM MAP (topology) Extended Message
OCIT-C Open Communication InTerface for road traffic Control systems
OTA Over-The-Air
PDU Packet Data Unit
POTI POsition and TIming
SAE Society of Automotive Engineers
SAM Service Advertisement Message
SPATEM Signal Phase And Timing Extended Message
SRM Signal Request Message
SSM Signal Status Message
SSP Service Specific Permission
SV Subject Vehicle
SW SoftWare
TPEG Transport Protocol Experts Group
TS Technical Specification
TV Target Vehicle
UC Use Case
V2V Vehicle to Vehicle
V2X Vehicle to Everything
VDP Vehicle Data Provider
4 CACC introduction
4.1 Background
In September 2015, the Transport Ministers of the G7 States and the European Commissioner for Transport agreed on a
declaration on automated and connected driving [i.1] with the objective of making a significant contribution towards
increasing road safety and improved mobility worldwide. The Declaration underlined the need to take appropriate steps
to establish a harmonised regulatory framework. In EU, deploying vehicles without a human driver is an option only for
restricted and well-defined areas. Several Member States already allow or have announced the adoption of legal acts to
make the testing of automated vehicles legal, e.g. on an approved test route or in an urban environment, where the
vehicle, the infrastructure and the environment are controlled.
The main motivation of CACC is to further reduce the time gap between vehicles compared to Adaptive Cruise Control
(ACC) system as defined in [i.8] and to improve the response to the speed variation of the target vehicle. This would
bring benefits to driver, road operator and potentially to society.
For the driver, the main benefit of CACC is related to gain the feeling of comfort, with a reduced and automatically
maintained (but safe) time gap, and to the better response to the speed variation of the target vehicle. In addition,
reduction of fuel consumption may be gained, thanks to the reduction of traffic jam.
For road operators, the main benefit of CACC may be related to increased road capacity and traffic efficiency. Study
has shown that highway lane capacity improvement may already be observed even with low penetration rate [i.9].
The social benefits of CACC may be related to increased road safety, reduced traffic jam and or environmental benefits.
Even though safety is not the primary goal of CACC, CACC can make ACC more attractive and convenient to drivers
by providing behaviour that is more responsive to preceding vehicle speed changes, that gives an enhanced sense of
safety because of its quicker response [i.9].
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11 ETSI TR 103 299 V2.1.1 (2019-06)
Nevertheless, special traffic management means may be needed, to optimize the traffic benefits of CACC on highway
or at urban environment. For example, some simulation studies have shown CACC may even bring negative effects on
lane capacity or even create traffic jams, until appropriate infrastructure support is provided. Example infrastructure
support may be specific lanes assigned for CACC pair and CACC string, where road side ITS-S may provide optimized
time gap and driving speed for CACC vehicles for maximizing lane capacity and traffic flow fluency.
4.2 CACC definition
CACC is an in-vehicle driving assistance system that adjusts automatically the vehicle speed to keep a target time gap
Δt with a target vehicle (TV) while keeping a minimum safety distance with it. CACC makes use of data received
target
from other vehicle ITS-Ss and/or from road side ITS-Ss via ITS network. The CACC includes at least one ITS-S
application (denoted as CACC application) that implements the application logic with the services provided by the
lower layers (Facilities, Networking & Transport layer, Access layer) as specified in ETSI EN 302 665 [i.2], and a set
of hardware components. The CACC application processes data received from other ITS-Ss and/or from on board
sensors, automatically determines vehicle speed and acceleration, and accordingly transmits control commands to
longitudinal control systems (e.g. brake, accelerator). In addition, the CACC application may be operating
simultaneously with other in-vehicle assistance systems or with other ITS-S applications such as pre-crash system,
lateral control system, etc. CACC is connected to the in-vehicle network and has access to in-vehicle sensor data. The
CACC can send control commands to acceleration/deceleration systems.
Multiple active CACC vehicles may follow each other, to form a vehicle group, denoted as CACC string in the present
document. A CACC string operational environment may change dynamically e.g. a CACC string may be divided into
two groups. A CACC string may be combined with another CACC string to form a new CACC string, or a CACC string
may be dismissed when all vehicles leave the string.
CACC may be operated in expressway or in urban/suburban environment.
Figure 1 illustrates an example functional overview of the CACC. The dotted red rectangle illustrates the focuses of the
present pre-standardization study scope. In general, the implementation of the hardware components is at the discretion
of implementers. Nevertheless, the requirements defined in the present document may impact on the HW/SW
implementation, for example, the compliance to the communication protocol standard is required to be considered in the
development of the communication systems.

Figure 1: Scope of the document
4.3 CACC target time gap
CACC target time gap Δt is the time gap set by CACC to follow a Target Vehicle (TV). The CACC adjusts the
target
acceleration, speed and/or brake to maintain the time gap Δt with TV to the Δt Time gap is the time interval between
target.
when a preceding vehicle's rear end and a following vehicle's front end passes the same location on the road surface,
assuming that the following vehicle's speed remains constant. The CACC target time gap is illustrated in Figure 2.
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12 ETSI TR 103 299 V2.1.1 (2019-06)

Figure 2: CACC target time gap
The Δt may be set according to different rules. In one possible setting, the Δt is proportional to vehicle speed
target target
when the vehicle speed is equal or higher than a predefined value. When v is below that value, a minimum distance d
s min
is required to be maintained. This setting rule is specified in ISO/DIS/20035 [i.12].
NOTE: In this setting rule, it is up to driver to ensure that the safety distance with TV is kept in order to avoid
potential collision risk.
In another possible setting, a minimum safety time gap is required to be maintained by CACC Δt , this minimum
min
safety time gap should be equal or higher than the time required for collision avoidance. When the Δt falls below Δt ,
min
the CACC application may be taken over by collision risk warning applications (automatic or manual), for example the
Longitudinal Collision Risk Warning [i.4] or Intersection Collision Risk warning applications [i.5].
| |
∆
Where:
• ∆t denotes minimum safety time gap.
min
• v denotes instant speed of SV.
s
• v denotes instant speed of TV.
t
• a denotes maximum deceleration of SV.
sv
4.4 CACC and automation levels
Depending on implementation strategy, the CACC system may be used to support different automated driving modes
(automation levels). In the scope of the present document, the following automation levels are used, as defined in SAE
J3016 [i.3]:
• Automation level 0 a
...