ISO 23792-2:2026

International
Standard
ISO 23792-2
First edition
Intelligent transport systems —
2026-03
Motorway chauffeur systems
(MCS) —
Part 2:
Requirements and test procedures
for discretionary lane change
Systèmes de transport intelligents — Systèmes de conduite
automatisée sur voie à chaussée séparée (MCS) —
Partie 2: Exigences et procédures d'essai pour le changement de
voie
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 2
5 Motorway chauffer systems (MCS) with discretionary lane change (DLC) . 5
5.1 DLC functionality .5
5.2 Lane change procedure . .5
6 Requirements . 6
6.1 General .6
6.2 State transitions .6
6.2.1 The states of DLC .7
6.2.2 The states of MCS .7
6.2.3 Transitions between the states .8
6.3 Detection function . .9
6.3.1 Detection of a sufficient gap and target lane availability .9
6.4 Driver interface . 13
6.4.1 Internal display elements . 13
6.4.2 External notifications . 13
6.4.3 Fallback ready user (FRU) input . 13
6.4.4 DLC manoeuvre .14
6.4.5 Failure reactions .14
7 Minimum performance . 14
7.1 Duration of the lane change manoeuvre .14
7.2 Operational limit . 15
8 Performance evaluation test methods .15
8.1 Environment conditions. 15
8.2 Test course conditions . 15
8.3 Test vehicle conditions . 15
8.4 Test system installation and configuration .16
8.5 Test procedures .16
8.5.1 Normal operation.16
8.5.2 Response to MCS cancellation condition during DLC .17
8.5.3 DLC conditions not met before starting the lane change procedure (Phase 1).17
8.5.4 DLC conditions not met after starting the lane change procedure (start of Phase
2) .18
8.5.5 Steering input during DLC .18
Annex A (informative) Permitted velocity for conducting a lane change . 19
Bibiography . .21

iii
Foreword
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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This document was prepared by Technical Committee ISO/TC 204, Intelligent transport systems.
A list of all parts in the ISO 23792 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
In order to operate a vehicle automatically on motorways, it is necessary for the automated driving system
(ADS) to be designed with the capability to cope with various conditions such as the driving environment,
status of other vehicles in the surroundings, traffic regulations, etc.
In addition, an ADS designed to operate on motorways can encounter various situations such as merging
into the main lane of traffic, adjusting the speed according to congested or freely flowing traffic, overtaking
other vehicles, or changing lanes when approaching an exit or lane closure.
For Level 3 automated driving, the ADS issues a request to the fallback-ready user (FRU) to take over driving
tasks when it cannot respond to certain conditions and situations.
The ISO 23793 series identifies the performance requirements of an ADS based on its capability to respond
to various conditions and situations. The requirements are derived in order to reliably transfer the vehicle
operation between the human driver and ADS, and for the safe operation by the ADS.
This series focuses on the system functionalities, keeping in mind that the FRU is assumed to be receptive
and properly responding to system requests to take over driving tasks, which is a prerequisite condition for
the use of Level 3 driving automation.
This document focuses on discretionary lane change (DLC) for motorway chauffeur systems (MCS). When
conditions are satisfied, a DLC-equipped MCS performs the entire DDT to change the current lane of travel
independently of the possibility of continuing operation within its current lane of travel. The system
monitors the driving environment in the adjacent lanes and operates the SV by adjusting the speed and
lateral position to move the SV to the intended lane. The MCS can delay the manoeuvre until the conditions
for initiating the lane change are satisfied or can cancel the lane change when conditions are not satisfied.
Activation of the DLC requires an engaged MCS performing in-lane driving.

v
International Standard ISO 23792-2:2026(en)
Intelligent transport systems — Motorway chauffeur systems
(MCS) —
Part 2:
Requirements and test procedures for discretionary lane
change
1 Scope
This document specifies the requirements for discretionary lane change (DLC) for motorway chauffeur
[1]
systems (MCS) that perform Level 3 automated driving on limited access motorways. It also specifies the
test procedures to verify the requirements. DLC is an additional functionality that can be added to an MCS
conforming to the general requirements specified in ISO/TS 23792-1.
Means related to setting a destination and selecting a route to reach the destination are not in the scope of
this document.
[2]
This document applies to the system installed in light vehicles.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO/TS 23792-1, Intelligent transport systems — Motorway chauffeur systems (MCS) — Part 1: Framework and
general requirements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
subject vehicle
SV
vehicle equipped with the system in question and related to the topic of discussion
3.2
lane
strip of road intended to accommodate a single line of moving vehicles, frequently defined by visible lane
marking (3.6)
3.3
initial lane
lane (3.2) in which the subject vehicle (3.1) is driving before starting the lane change manoeuvre (3.7)
Note 1 to entry: See Figure 2 for a description of lanes and vehicles.
3.4
target lane
lane (3.2) next to the initial lane (3.3), which the subject vehicle (3.1) targets to make a lane change
Note 1 to entry: See Figure 2 for a description of lanes and vehicles.
3.5
adjacent to target lane
lane (3.2) next to the target lane (3.4), which the subject vehicle (3.1) targets to make a lane change
3.6
lane marking
delineators or markings intentionally placed on the borderline of the lane (3.2)
EXAMPLE Botts' dots.
3.7
lane change manoeuvre
addition of a lateral movement to the current longitudinal motion of the subject vehicle (3.1), which the
system automatically executes with the sole purpose of changing lanes (3.2) from its initial lane (3.3) to an
adjacent lane with the same direction of travel
3.8
time gap
t
gap
value calculated from vehicle speed, v, and clearance, c
Note 1 to entry: The time gap is calculated using Formula (1):
t = c/v (1)
gap
Note 2 to entry: to entry: If the subject vehicle (3.1) is one of vehicles for which the time gap is being calculated, as in
Figure 1, the subject vehicle speed should be taken as the value for v.
Key
c clearance
v vehicle speed
Figure 1 — Time gap
3.9
gap search
function of searching for a sufficient gap to make a lane (3.2) change into the target lane (3.4)
4 Symbols and abbreviated terms
For the purposes of this document, the abbreviated terms listed in Table 1 and the symbols listed in Table 2
apply.
Table 1 — Abbreviated terms
Abbreviated terms Definition
ADS automated driving system
adjacent to target lane following vehicle, i.e. immediate following vehicle in the adjacent
AFV
to target lane before starting a lane change manoeuvre
adjacent to target lane leading vehicle, i.e. immediate leading vehicle in the adjacent to
ALV
target lane before starting a lane change manoeuvre
DDT dynamic driving task
DLC discretionary lane change
FRU fallback-ready user
initial lane following vehicle, i.e. immediate following vehicle in the initial lane before
IFV
starting a lane change manoeuvre
initial lane leading vehicle, i.e. immediate leading vehicle in the initial lane before starting
ILV
a lane change manoeuvre
MCS motorway chauffeur systems
ODD operational design domain
RTI request to intervene
SV subject vehicle
target lane following vehicle, i.e. immediate following vehicle in the target lane before
TFV
starting a lane change manoeuvre
target lane leading vehicle, i.e. immediate leading vehicle in the target lane before starting
TLV
a lane change manoeuvre
Table 2 — Symbols
Symbols Definition
a maximum lateral acceleration the subject vehicle may generate during the DLC
Lat_max
a maximum lateral jerk that the subject vehicle may generate during the DLC
Lat_Jerk_max
c clearance
necessary deceleration to be generated by the SV for the v to become equivalent to v
SV TLV
d
SV
and to maintain the required distance between the TLV and the SV at steady state
d deceleration assumed to be performed by the TFV
TFV
d deceleration assumed to be performed by the TLV
TLV
required distance between the SV and the TLV assumed to be remaining at the end of the
D
SV_TLV
lane change
minimum distance to be maintained between the SV and the TLV at low speed, based on
D
SV_TLVmin
a predetermined distance limit
relative distance between the TFV and the SV that would shorten while TFV decelerates
D
TFVdec
at an assumed level (d )
TFV
required distance between the TFV and the SV assumed to be remaining at the end of
D
TFV_SV
the lane change
minimum distance to be maintained between the TFV and the SV at low speed, based on
D
TFV_SVmin
a predetermined distance limit
D detection range required to detect the distance between the SV and the TFV
TFVrange
relative distance between the TFV and the SV that would shorten while TFV is assumed
D
TFVreact
to react (t ) to start decelerating
TFVreact
required distance to be detected between the TFV and the SV to determine a sufficient
D
TFVreq
gap for executing a lane change
relative distance between the TLV and the SV that would shorten while TLV decelerates
D
TLVdec
at an assumed level (d )
TLV
TTabablele 2 2 ((ccoonnttiinnueuedd))
Symbols Definition
relative distance between the TLV and the SV that would shorten while TLV is assumed
D
TLVreact
to react (t ) to start decelerating
TLVreact
required distance to be detected between the TLV and the SV to determine a sufficient
D
TLVreq
gap for executing a lane change
t time gap
gap
t time gap between the SV and the TLV
gapSV_TLV
t time gap between the TFV and the SV
gapTFV_SV
reaction time of the SV to start deceleration after the SV starts a lane change manoeuvre
t
SVreact
towards the target lane
assumed reaction time of the TFV to start the deceleration, after the SV starts a lane
t
TFVreact
change manoeuvre towards the target lane
assumed reaction time of the TLV to start the deceleration, after the SV starts a lane change
t
TLVreact
manoeuvre towards the target lane
v vehicle speed
v speed limit of the motorway
limit
v current velocity of the SV as observed in real time
SV
v velocity of the following vehicle approaching in the target lane
TFV
v velocity of the leading vehicle in the target lane
TLV
Figure 2 provides a description of the lanes and vehicles associated with the lane change. See Table 1 for the
relevant abbreviated terms.
Key
1 IFV
2 SV
3 ILV
4 TLV
5 ALV
6 AFV
7 TFV
a
Initial lane.
b
Target lane.
c
Adjacent to target lane.
Figure 2 — Description of lanes and vehicles

5 Motorway chauffer systems (MCS) with discretionary lane change (DLC)
5.1 DLC functionality
A DLC-functionality-equipped MCS (hereafter referred to as a “system”) performs the entire dynamic driving
task (DDT) for lane changes when a manufacturer-defined motivation for lane change exists. Motivation for
a lane change is based upon conditions designed for the system. Examples of possible discretionary lane
change motivations can be:
a) FRU makes an input to request a lane change;
b) to follow the lane of travel to keep the planned route;
c) to overtake the ILV.
5.2 Lane change procedure
The DLC is executed through the following phases. Figure 3 illustrates the position of the SV at the start of
each phase.
Figure 3 — Phases of DLC
— Phase 0: Lane change functionality is idle and is in the standby state (refer to 6.2.1.3). Motivation for lane
change does not exist.
— Phase 1: Motivation for a lane change exists. The system executes the gap search.
— Phase 2: start of a lane change procedure. The system will notify the FRU of the start of the procedure.
The procedure is indicated to surrounding vehicles with the turn indicator. It is up to the manufacturer
to determine how the lane change procedure is cancelled if the lane change manoeuvre cannot be started
within a certain time period.
— Phase 3: The sufficient gap conditions have been confirmed and lane change manoeuvre has started and
DLC is in the active state (refer to 6.2.1.4), but the SV has not yet left the initial lane. The SV leaves the
initial lane after the turn signal is indicated for the specified period of time (refer to 6.2.1.4).
— Phase 4: The system is performing a lane change and the SV has entered the target lane with at least one
tyre in contact with the lane marking (refer to 6.2.1.4).
— Phase 5: The SV has almost finished performing the lane change (point of no return), i.e. the manoeuvre
has reached a sufficient point for it to be considered that the target lane is now the travel lane. The lane
change manoeuvre may therefore be completed even though a new vehicle is detected to be approaching
from behind, within the area of the sufficient gap. The SV should be positioned with at least half the
lateral position at the front tyres within the target lane, but not completely within the target lane.
— Phase 6: The SV has finished performing the lane change and all tyres are completely within the target
lane. The lane change manoeuvre is therefore completed and the DLC returns to the standby state (refer
to 6.2.1.3). Lane centring may be performed separately in order to position the vehicle within the target
lane.
6 Requirements
6.1 General
The system performs the lane change manoeuvre with the existence of a FRU. The system shall have
detection, driver interface, manoeuvring and failure reaction functions as described in this clause (see also
6.4.5).
6.2 State transitions
The system shall, at a minimum, provide the operations and state transitions described in Figure 4.
Key
DL1 DLC turned on
DL2 DLC conditions to start manoeuvre are satisfied
DL3 DLC manoeuvre completed
DL4 DLC turned off
M1 MCS turned on
M2 Engagement conditions are satisfied
M3 FRU override
M5 Disengagement-triggering condition detected
M6 FRU override
M7 MCS turned off
M8 MCS turned off
Figure 4 — DLC state diagram
6.2.1 The states of DLC
6.2.1.1 DLC off
DLC functions are not performed in the DLC off state. DLC is turned off or a failure of DLC is detected.
6.2.1.2 DLC on
DLC can automatically transition to DLC on upon entering MCS normal state, thus entering DLC standby, in
case MCS is engaged. It is also allowed that the DLC first starts from DLC off in case MCS is engaged.
6.2.1.3 DLC standby (Phases 0 – 2 and 6)
The system evaluates the conditions to perform a lane change using information on surroundings which is
obtained from sensors installed on the vehicle. This state corresponds to Phase 0 – Phase 2 and Phase 6 of
the lane change procedure (see Figure 3).
6.2.1.4 DLC Active (Phases 3 – 5)
The DLC manoeuvre is performed. This state corresponds to Phase 3 – Phase 5 of the lane change procedure
(see Figure 3). No SV tyre shall touch the lane marker earlier than 3 s after activation of the turn signal. The
gap confirmation shall continue throughout the lane change manoeuvre until reaching the point of no return
defined in Phase 5. Once at least one tyre of the SV is in contact with and crosses the lane marking (Phase 4),
the manoeuvre shall be executed with a single lateral velocity peak, unless a cancellation condition or
insufficient gap condition has been detected.
6.2.2 The states of MCS
6.2.2.1 MCS off
In the off state, the MCS including the DLC functionality is turned off. Monitoring functions can be active in
order to detect conditions that influence transitions.
6.2.2.2 MCS standby
In addition to the conditions required in ISO/TS 23792-1, the system shall determine if engagement conditions
are satisfied by continuously monitoring, at a minimum, the conditions of the driving environment, MCS and
SV that are relevant for DLC.
6.2.2.3 MCS requesting fallback during lane change manoeuvre
In the requesting fallback state, the system shall have the following means:
— extend its operation of the lane change procedure and continue to perform the DDT for a sufficient length
of time for the FRU to perform the fallback, unless the transition condition M6 or M7 in Figure 4, as
defined in ISO/TS 23792-1, is satisfied;
— whilst performing the DDT, prioritize keeping distance from surrounding vehicles and if possible, bring
the SV fully into either the initial or the target lane.
In the requesting fallback state, in case the FRU does not respond adequately to the request to intervene
(RTI), the system should in addition:
— perform a minimal risk manoeuvre (MRM) by manoeuvring the SV into either the initial or target lane
and if capable, either define and manoeuvre to a stopping location or reach minimal risk condition
(MRC), or both, prioritizing maintaining distance from the detected obstacles including the vehicles in
the initial, target and adjacent lanes before bringing the SV to a complete stop.

6.2.2.4 MCS normal
In the normal state, where DLC function is activated, the system shall:
— perform the entire DDT in accordance with the minimum DDT performance requirements of those for
DLC;
— detect the occurrence of disengagement-triggering conditions and direct disengagement conditions by
continuously monitoring, at a minimum, conditions of the driving environment, MCS system, and SV,
which apply to DLC.
6.2.3 Transitions between the states
The transitions between states in Figure 4 are described as follows:
— transitions M1 – M8 follow ISO/TS 23792-1 unless specified in the following list item;
— the DLC-specific transitions (M2, M5 and DL1 – DL4) are described in the following subclauses.
6.2.3.1 MCS standby to normal (M2)
When the driver turns off the DLC functionality availability (e.g. in a setting menu) while the SV is in the
fast lane, MCS will potentially wait until the SV leaves the fast lane, then transition to Normal state to follow
applicable local rules so that MCS without DLC functionality would become available in lanes other than the
fast lane.
6.2.3.2 MCS normal to requesting fallback (M5)
In addition to the conditions defined in ISO/TS 23792-1, the system may transition from its normal state to
the requesting fa
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