ISO 22178:2009

INTERNATIONAL ISO
STANDARD 22178
First edition
2009-04-01

Intelligent transport systems — Low
speed following (LSF) systems —
Performance requirements and test
procedures
Systèmes intelligents de transport — Systèmes suiveurs à basse
vitesse (LSF) — Exigences de performance et méthodes d'essai




Reference number
ISO 22178:2009(E)
©
ISO 2009

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ISO 22178:2009(E)
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ISO 22178:2009(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
5 Classification — types of LSF systems. 4
6 Requirements . 4
6.1 Basic control strategy . 4
6.2 Applicable target vehicle . 6
6.3 Functionality. 8
6.4 Basic driver interface and intervention capabilities . 10
6.5 Operational limits. 11
6.6 Activation of brake lights. 12
6.7 Failure reactions . 12
6.8 Combination with other systems . 13
7 Performance evaluation test methods. 13
7.1 Environmental conditions. 13
7.2 Test target specification . 14
7.3 Detection zone test. 14
7.4 Target discrimination test. 15
7.5 Automatic deceleration test. 17
7.6 Automatic retargeting capability test (type 2 LSF system only). 18
7.7 Curve capability test. 19
Annex A (normative) Technical information. 23
Bibliography . 28

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ISO 22178:2009(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 22178 was prepared by Technical Committee ISO/TC 204, Intelligent transport systems.
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ISO 22178:2009(E)
Introduction
The main system function of low speed following is to control vehicle speed adaptively to a forward vehicle by
using information about: (1) ranging to forward vehicles, (2) the motion of the subject (LSF equipped) vehicle
and (3) driver commands (see Figure 1 — Functional LSF elements). Based upon the information acquired,
the controller (identified as “LSF control strategy” in Figure 1) sends commands to actuators for carrying out
its longitudinal control strategy and also sends status information to the driver.

Figure 1 — Functional LSF elements
The goal of LSF is a partial automation of the longitudinal vehicle control to reduce the driver’s workload.
This International Standard may be used as a system level standard by other standards, which extend the
LSF to a more detailed standard, e.g. for specific detection and ranging sensor concepts or higher level of
functionality. Therefore, issues like specific requirements for the detection and ranging sensor function and
performance or communication links for co-operative solutions will not be considered here.

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INTERNATIONAL STANDARD ISO 22178:2009(E)

Intelligent transport systems — Low speed following (LSF)
systems — Performance requirements and test procedures
1 Scope
This International Standard contains the basic control strategy, minimum functionality requirements, basic
driver-interface elements, minimum requirements for diagnostics and reaction to failure, and performance test
procedures for low speed following (LSF) systems.
An LSF system is primarily intended to reduce the driver’s workload of repeatedly operating the accelerator
and the brake pedal under congested traffic in order to keep a proper following distance behind the target
vehicle for a relatively long period on roadways where there are no objects like pedestrians and bicyclists who
might interrupt motorized traffic flow. An LSF system provides automatic car-following at lower speed by use
of a driver interface mechanism and a speed adjustment system. The LSF system does not normally provide
speed regulator control.
2 Normative references
The following referenced documents are indispensable for the application 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 2575, Road vehicles — Symbols for controls, indicators and tell-tales
1)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
clearance
distance from the forward vehicle's trailing surface to the subject vehicle's leading surface
3.2
congested traffic
traffic condition where the driver, at lower speed, repeatedly starts, follows a forward vehicle, and stops in
order to keep a proper following distance behind the forward vehicle
3.3
cutting out
situation in which the target vehicle changes lanes from behind a preceding vehicle

1) Definitions are in accordance with the Glossary of ISO/TC 204/WG 14.
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ISO 22178:2009(E)
3.4
forward vehicle
vehicle in front of, and moving in the same direction and travelling on the same roadway as, the subject
vehicle
3.5
go operation
driver action to convey to the system the intention of placing the subject vehicle in motion
EXAMPLE Operation of the accelerator pedal and operation of a switch for starting the subject vehicle.
3.6
low speed following
LSF
function that allows the subject vehicle to follow a forward vehicle in low speed ranges such as congested
traffic at an appropriate distance by controlling the engine and/or power train and the brakes
3.7
LSF following state
condition where the system controls the clearance to the target vehicle according to the selected time gap
3.8
LSF hold state
condition where the system controls the subject vehicle to be kept stationary
3.9
LSF retargeting state
temporary target-lost period during a transition to the next target vehicle
3.10
maximum operational speed
maximum speed the LSF system can attain while in following control
3.11
minimum operational speed
minimum speed the LSF system can maintain while in following control
3.12
slow moving object
object in front of the subject vehicle that is moving at less than MAX [1,0 m/s, 10 % of the subject vehicle
speed] in the direction of the centreline of the subject vehicle
3.13
stationary object
object in front of the subject vehicle that is stationary
3.14
steady state
condition whereby the value of the described parameter does not change with respect to time, distance, etc.
3.15
subject vehicle
vehicle equipped with the LSF system in question and related to the topic of discussion
3.16
target vehicle
vehicle that the subject vehicle follows
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ISO 22178:2009(E)
3.17
time gap
value calculated from vehicle speed, v, divided by clearance, c
NOTE See Figure 2.

Figure 2 — Time gap
4 Symbols and abbreviated terms
2
CTT Coefficient for Test Target (for infrared reflectors) (m /sr)
c clearance, inter vehicle distance (m)
c minimum clearance under steady state conditions for all speeds (including hold state) (m)
min
c (v) minimum steady state clearance at speed v (m)
min
d distance, maximum detection range on straight roads (m)
max
d distance between source and projected area A (m)
A
d distance above which the system shall not regard a target vehicle (m)
target_limit
d distance below which detection of a target vehicle is not required (m)
0
d distance below which neither distance measurement nor determination of relative speed is
1
required (m)
l length (of a side of a RADAR test reflector) (m)
R curve radius (m)
R minimum curve radius (m)
min
2
RCS RADAR Cross Section (m )
v true subject vehicle speed over ground (m/s)
v vehicle speed as it enters a curve of radius R (m/s)
circle_start
v maximum operational speed (m/s)
max
v minimum operational speed (m/s)
min
v vehicle speed at the end of a test (m/s)
vehicle_end
v vehicle speed at the start of a test (m/s)
vehicle_start
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ISO 22178:2009(E)
2
A projected (utilized) area (m )
2
A illuminated surface (m )
t
2
E intensity of irradiation (W/m )
t
I radiated intensity (W/sr)
I radiated intensity in a given direction (W/sr)
ref
λ wavelength (m)
τ gap, time gap between vehicles (s)
τ maximum selectable time gap (s)
max
τ maximum possible steady state time gap at a given speed v (s)
max(v)
τ minimum selectable time gap (s)
min
τ minimum steady state time gap at speed v (s)
min(v)
Φ radiation source (W)
Φ radiated power (W)
ref
Φ incident radiated power (W)
t
Ω solid angle (sr)
Ω solid angle of the source (sr)
0
5 Classification — types of LSF systems
Two types of LSF systems are addressed in this International Standard.
The type 1 LSF system follows the target vehicle that is recognized when the driver activates the system.
The type 2 LSF system follows the target vehicle that is recognized when the driver activates the system and
it retargets the target vehicle automatically until the system is deactivated.
6 Requirements
6.1 Basic control strategy
LSF systems shall, as a minimum, provide the following control strategy and state transitions (see Figure 3).
The following constitutes the fundamental behaviour of LSF systems.
⎯ In the LSF following state, the vehicle speed will be controlled automatically to maintain a clearance to a
target vehicle (for car-following capability, see 6.3.2).
⎯ (Type 2 LSF system) In the LSF following state, a new target vehicle will be chosen automatically (for
automatic retargeting capability, see 6.3.3).
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ISO 22178:2009(E)
⎯ (Type 2 LSF system) In the LSF retargeting state, the subject vehicle shall not accelerate (for automatic
retargeting capability, see 6.3.3).
⎯ After the subject vehicle has come to a stop, the system shall transfer to the LSF hold or stand-by state
(for deactivation conditions, see 6.3.5).
⎯ In the LSF hold state, automatic brake control will be accomplished for keeping the subject vehicle
stationary (for hold capability, see 6.3.4).

a
The transition is driven after self-diagnostics by manual operation or automatically performed.
b
The transition is driven by a manual operation of the on-off switch of the LSF system. Automatic switch-off function
can be activated upon detecting any failure.
c
The driver’s operation to deactivate the system or the conditions specified in 6.3.5.
d
Optional state.
Figure 3 — LSF states and transitions
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ISO 22178:2009(E)
6.2 Applicable target vehicle
6.2.1 General
The LSF system shall regard the forward vehicles that conform to the following conditions from 6.2.2 to 6.2.4
as a target vehicle.
6.2.2 Detection targets
The LSF system shall detect moving vehicles.
The LSF system shall regard a stopped vehicle that was tracked before it stopped as a target vehicle.
It is optional to design LSF systems to regard an object that is already stationary or slow-moving when
detected as a target vehicle. When stationary objects or slow-moving objects are not regarded as a target
vehicle, the driver shall be informed, as a minimum, by a statement in the vehicle owner’s manual.
6.2.3 Detection range on straight roads

Key
1 subject vehicle
2 forward vehicle
a
Detection of vehicle not required.
b
Detection of vehicle required.
c
Detection of vehicle and determination of range.
Figure 4 — Range of detection
If a forward vehicle is present within the distance range of d to d , the LSF system shall measure the range
1 max
between the forward and subject vehicles (see Figure 4). Within this range, the forward vehicle shall be
detected within a lateral area of at least the subject vehicle width.
d = τ (v ) × v
max max max max
If a forward vehicle is present within the distance range of d to d , the LSF system shall detect the presence
0 1
of the vehicle but is not required to measure the range to the vehicle nor the relative speed between the
forward and subject vehicles. If a forward vehicle is detected within this range and the distance cannot be
determined, the system shall inhibit automatic acceleration.
d = c (v )
1 min min
If a forward vehicle is present at a distance less than d , the LSF system is not required to detect the presence
0
of the vehicle.
d = 2 m
0
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ISO 22178:2009(E)
6.2.4 Target discrimination
If there is more than one forward vehicle on straight roads, the closest of these vehicles (see Figure 5) in the
subject vehicle's path shall be selected for LSF control in typical LSF situations as represented by the test
scenario (for the target discrimination test, see 7.4).

Key
1 subject vehicle
2 forward vehicle in the subject vehicle’s path
3 forward vehicle in the adjacent lane
Figure 5 — Target discrimination
If a forward vehicle is in the distance farther than d , the LSF system shall not regard it as a target
target_limit
vehicle (see Figure 6).
d =MAX⎡⎤τ (vv)×× 3 , 36
{ }
max
target_limit ⎣⎦

Key
1 subject vehicle
2 forward vehicle
a
LSF system may regard it as a target vehicle.
b
LSF system shall not regard it as a target vehicle.
Figure 6 — Range of target vehicle
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ISO 22178:2009(E)
6.3 Functionality
6.3.1 Activation conditions
The following conditions must be satisfied in order to transition to the active state.
⎯ The system shall be activated by a driver.
⎯ The speed of the subject vehicle shall not exceed the system’s maximum operation speed.
⎯ The subject vehicle shall already detect the target vehicle.
⎯ The deactivation conditions are not fulfilled.
⎯ The system does not detect any failure.
When the subject vehicle is stopped, it is permissible for the LSF system with hold capability to transition to
the LSF hold state even while the driver is operating the brake pedal.
6.3.2 Car-following capability
In the LSF following state, the speed of the subject vehicle shall be controlled automatically in the range of
v to v to maintain the intended clearance from the target vehicle.
min max
The LSF system shall decelerate, within its limited deceleration capability, to v behind a stopping target
min
vehicle that is already tracked.
Under the steady state condition, the LSF system shall comply with the minimum clearance limit as defined
in 6.3.2.1.
Under transient conditions, the clearance may temporarily fall below the desired distance. If such a situation
occurs, the system shall adjust the clearance to attain the desired distance.
6.3.2.1 Clearance capability
τ shall be the minimum selectable time gap for following under steady state conditions for all speeds v.
min
τ (v) shall be greater than or equal to τ = 1,0 s.
min min
c shall be the minimum clearance for following under steady state conditions for all speeds v. c (v) shall
min min
be greater than or equal to c = 2,0 m.
min
Under steady state conditions, the clearance shall not be below MAX [c , (τ × v)].
min min
6.3.2.2 Curve capability
The LSF system shall enable steady state vehicle following with a time gap of τ on a curve with a radius of
max
R greater than or equal to R = 125 m.
min
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ISO 22178:2009(E)
6.3.3 Automatic retargeting capability (type 2 LSF system only)
The type 2 LSF system shall have an automatic retargeting capability to detect a next target vehicle and
switch the target at least in the following instances:
⎯ cutting in by other vehicles;
⎯ cutting out by target vehicle.
In the LSF retargeting state, the vehicle speed may be controlled.
In the LSF retargeting state, acceleration shall not be allowed.
The LSF retargeting state shall transfer to the LSF following state at the instant of switching to the new target
vehicle.
6.3.4 Hold capability (optional)
The LSF system with v = 0 may have hold capability as an option.
min
The LSF system with hold capability shall automatically transfer to the LSF hold state when the subject vehicle
comes to stop.
The transition from hold state to following state is enabled by the driver’s go operation and can only be
effected if the subject vehicle has already detected the target vehicle.
6.3.5 Deactivation conditions
The system shall transfer from the active state to the stand-by state when any of the following conditions
occur.
⎯ In the LSF following and the LSF retargeting states, braking by the driver shall deactivate LSF system at
least if the driver-initiated brake force demand is higher than the LSF-initiated brake force.
⎯ In the LSF following and the LSF retargeting states, the system shall be deactivated when the subject
vehicle speed exceeds v .
max
⎯ In the LSF following and the LSF retargeting states, the system without hold capability shall be
deactivated when the subject vehicle speed drops below v . In the case of v = 0, the system shall be
min min
deactivated within 3 s after the subject vehicle has come to a stop.
⎯ In the LSF following state, the type 1 LSF system shall be deactivated when cutting in/out occurs or when
no target vehicle is present.
⎯ If the target vehicle comes closer than d and is no longer detected, the type 1 and type 2 LSF systems
0
shall inhibit automatic acceleration and may continue braking.
⎯ In the LSF retargeting state, the type 2 LSF system shall be deactivated either when the duration of this
state exceeds τ or when the subject vehicle reaches the location where the target vehicle was when it
max
was lost.
NOTE τ is the maximum selectable time gap, i.e. it is the clearance divided by the subject vehicle speed
max
(> 0) normally used and at which a driver expects retargeting.
⎯ In the LSF hold state, braking by the driver may not necessarily deactivate the LSF system.
⎯ In the LSF hold state, when the system deactivates automatically, the deactivate condition shall be clearly
stated in the owner’s manual of the vehicle and a notification shall be provided when deactivation occurs.
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ISO 22178:2009(E)
6.4 Basic driver interface and intervention capabilities
6.4.1 General
The system shall provide the following controls and intervention capabilities.
6.4.2 Operation elements and system reactions
6.4.2.1 The LSF system shall not lead to a significant transient reduction of braking in response to the
driver's braking input even when the LSF system has been braking automatically.
6.4.2.2 The larger of the power demands from either the driver or the LSF system will be used to drive
the engine power actuator (e.g. throttle actuator). This always gives the driver authority to override the LSF
system engine power control.
If the power demand of the driver is greater than that of the LSF system, automatic braking shall be
disengaged with an immediate brake force release. A driver intervention on the accelerator pedal shall not
lead to a significant delay of response to driver's input.
6.4.2.3 Automatic brake activation shall not lead to locked wheels for periods longer than anti lock
devices (ABS) would allow. This need not require an anti lock device (ABS) system.
6.4.2.4 Automatic power control by LSF shall not lead to excessive positive wheel slip for periods longer
than traction control would allow. This need not require a traction control system.
6.4.2.5 The LSF system may automatically adjust the clearance without action by the driver in order to
respond to the driving environment (e.g. poor weather). However, the adjusted clearance shall not be less
than the minimum clearance selected by the driver.
6.4.2.6 If the system allows the driver to select a desired clearance and/or time gap, the selection method
shall conform to either one of the following.
a) If the system retains the last selected clearance and/or time gap after it is switched to LSF off, the
clearance and/or time gap shall be clearly presented to the driver at least upon system activation.
b) If the system does not retain the last selected clearance and/or time gap after it is switched to LSF off, the
clearance and/or time gap shall be set to a predefined default value.
6.4.3 Display elements
6.4.3.1 In the stand-by state, an active-ready signal meaning that the LSF system is ready to transition
from stand-by state to active state, which will be used for the adaptation of the control, is recommended.
6.4.3.2 In the active state, the type 2 LSF system shall have visual display indicating when a target
vehicle is detected.
6.4.3.3 The system shall have visual display indicating when the system is in the active state.
6.4.3.4 If the LSF system shuts down or is not available due to a failure, the driver shall be informed.
6.4.4 Symbols
If symbols are used to identify LSF function or malfunction, standardized symbols in accordance with
ISO 2575 shall be used.
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ISO 22178:2009(E)
6.5 Operational limits
v shall not exceed 13,9 m/s.
max
v shall not exceed 1,39 m/s (0 u v u 1,39 m/s).
min min
There shall not be a sudden brake force release in the case of an automatic deactivation of the LSF system.
2
The average automatic deceleration of LSF systems shall not exceed 3,5 m/s (average over 2 s) when the
2
vehicle is travelling above 20 m/s and 5 m/s (average over 2 s) when the vehicle is travelling below 5 m/s, as
shown in Figure 7. The vehicle speed range 0 m/s to 13,9 m/s only applies to the LSF systems.

Key
X subject vehicle speed, expressed in m/s
2
Y maximum deceleration, expressed in m/s
Figure 7 — Maximum deceleration
3
The average rate of change of automatic deceleration (negative jerk) shall not exceed 2,5 m/s (average
3
over 1 s) when the vehicle is travelling above 20 m/s and 5 m/s (average over 1 s) when the vehicle is
travelling below 5 m/s, as shown in Figure 8. The vehicle speed range 0 m/s to 13,9 m/s only applies to the
LSF systems.

Key
X subject vehicle speed, expressed in m/s
3
Y negative jerk, expressed in m/s
Figure 8 — Negative jerk
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ISO 22178:2009(E)
2
The average automatic acceleration of LSF systems shall not exceed 2 m/s (average over 2 s) when the
2
vehicle is travelling above 20 m/s and 4 m/s (average over 2 s) when the vehicle is travelling below 5 m/s, as
shown in Figure 9. The vehicle speed range 0 m/s to 13,9 m/s only applies to the LSF systems.

Key
X subject vehicle speed, expressed in m/s
2
Y automatic acceleration, expressed in m/s
Figure 9 — Automatic acceleration
6.6 Activation of brake lights
If the LSF system applies automatic service braking, the brake lights shall be illuminated. When the LSF
system applies other deceleration devices, the system may illuminate the brake lights. The brake lights shall
be illuminated within 350 ms after the LSF system initiates the service brake. To prevent irritating brake light
flickering, the brake light may remain on for a reasonable time after the LSF initiated braking has ended.
6.7 Failure reactions
Table 1 gives the required reactions to failures depending on which subsystem fails.
⎯ The failures described in Table 1 shall result in immediate notification to the driver. The notification shall
remain active until the system is switched off.
⎯ The reactivation of the LSF system shall be prohibited until a successful self test, initiated by either
ignition off/on or LSF-off/on, is accomplished.
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