ISO/TS 15624:2001

TECHNICAL ISO/TS
SPECIFICATION 15624
First edition
2001-01-15
Transport information and control
systems — Traffic Impediment Warning
Systems (TIWS) — System requirements
Systèmes de commande et d'information des transports — Systèmes
d'avertissement des obstacles au trafic (TIWS) — Exigences des systèmes
Reference number
©
ISO 2001
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ii © ISO 2001 – All rights reserved

Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Terms and definitions .1
3 Specifications and requirements .2
3.1 General specifications .2
3.2 Classifications.3
3.3 Objects constituting traffic impediments and detection coverage .3
3.4 Types of sensors .4
3.5 Provision of information .4
3.6 Range of information provision to drivers.6
3.7 CCTV camera installation interval.8
4 System testing method .8
4.1 System performance test.8
4.2 System function test .8
Annex A (informative) Incidents of traffic impediment events .9
Annex B (informative) Issues to be addressed and not addressed.12
Annex C (informative) Place for introducing a system.13
Annex D (informative) Specific example of CCTV camera monitoring range .15
Annex E (informative) Symbols .16
Annex F (informative) Example for providing contents of information.17
Annex G (informative) Specific example of variable message sign installation interval.18
Annex H (informative) Specific example of system reaction time .22
Annex I (informative) Camera installation interval.24
Annex J (informative) System testing method .27
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
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Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
The main task of technical committees is to prepare International Standards. Draft International Standards adopted
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Standard requires approval by at least 75 % of the member bodies casting a vote.
In other circumstances, particularly when there is an urgent market requirement for such documents, a technical
committee may decide to publish other types of normative document:
� an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in an
ISO working group and is accepted for publication if it is approved by more than 50 % of the members of the
parent committee casting a vote;
� an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting a
vote.
An ISO/PAS or ISO/TS is reviewed every three years with a view to deciding whether it can be transformed into an
International Standard.
Attention is drawn to the possibility that some of the elements of this Technical Specification may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TS 15624 was prepared by Technical Committee ISO/TC 204, Transport information and control systems.
Annexes A to J of this Technical Specification are for information only.
iv © ISO 2001 – All rights reserved

Introduction
Once an accident occurs on a highway, the accident and congestion and other hazardous conditions may result in
blocking of the lanes. This often leads to a situation where the safety of the traffic flow behind the accident cannot
be guaranteed. Conventionally, it could take more than ten minutes before the occurrence of an accident is known,
since accidents are generally reported by emergency telephones installed along the road. In the case of minor
accidents, drivers usually drive away without reporting the incident. Detection, therefore, is very difficult, and there
are cases where damaged facilities often obstruct traffic flow.
The main system function of a Traffic Impediment Warning System (TIWS) is to secure a smooth and safe flow of
traffic subsequent to an accident, and can be achieved by: quick detection of an accident, rapid processing of the
initial activities surrounding the accident and removal of impediments, dissipating traffic congestion at an early
stage, and providing information to following vehicles.
The goal of TIWS is a partial automation of the traffic impediment information collection and provision, and the
reduction of the workload of the driver with the aim to support and relieve the driver and the traffic system operator
in a convenient manner.
This Technical Specification may be used as a system level standard by other standards, which extends the TIWS
to a more detailed standard e.g. for specific sensor concepts or higher level of functionality. So, issues like specific
requirements for the sensor function and performance or communication links for cooperative solutions will not be
considered in this document.
TECHNICAL SPECIFICATION ISO/TS 15624:2001(E)
Transport information and control systems — Traffic Impediment
Warning Systems (TIWS) — System requirements
1 Scope
This Technical Specification specifies system requirements for Traffic Impediment Warning Systems (TIWS). The
purposes of the warning system are that information collected by the infrastructure is automatically and quickly
provided to vehicles and reported to the traffic system operator, so vehicles can avoid secondary accidents. A
major function of the system is to save lives by speedier rescue activities and, a quicker clearing up of accident-
caused congestion. This Technical Specification focuses on closed circuit television (CCTV) cameras as the
sensors, to detect traffic impediments using image processing and variable message signs as the communication
method to provide information to drivers.
2 Terms and definitions
For the purposes of this Technical Specification, the following terms and definitions apply.
2.1
Traffic Impediment Warning Systems
TIWS
system that automatically detects traffic impediments by employing sensors, reports occurrences of accidents to a
traffic system operator, and provides information on the presence of traffic impediments to following vehicles before
the cause is visible to them
NOTE See annex A.
2.2
stopped vehicles
vehicle that has stopped in a traffic lane or on the shoulder of the roadway
2.3
slow moving vehicles
vehicle travelling at or below “A” km/h within a traffic flow
NOTE The value for “A” is to be determined according to the road configuration and speed limit.
2.4
judgement distance
distance travelled by a vehicle until the driver judges what action is to be taken after having received information
about a traffic impediment
2.5
reaction distance
distance travelled by a vehicle from the time the driver judged what action to take until the time the brake is applied
after having been notified of a traffic impediment
2.6
braking distance
distance the vehicle needs in order to stop after the brakes have been applied
2.7
camera blind spot range
distance from the location where a camera is installed to the beginning of the area over which the camera is able to
monitor traffic impediments
NOTE The camera is unable to monitor traffic impediments in this blind area.
2.8
out-of-sight range
distance from the point where a variable message sign becomes no longer readable to the place where the
variable message sign is located
2.9
average spacing
average distance between the front of one vehicle and another in a continuous traffic flow
NOTE This parameter is inversely proportional to the density of traffic.
3 Specifications and requirements
3.1 General specifications
The system configuration should be in accordance with Figure 1.
a
The information collection subsystems consist of equipment to detect traffic impediments by various sensors installed on, or
alongside, a road. This Techical Specification focuses on the detection of traffic impediments from image processing by using
CCTV cameras serving as sensors to automatically detect traffic impediments.
b
The processing and judgement subsystem processes the information detected from a camera, and/or a sequence of
cameras, and determines the occurrence of traffic impediments.
c
The monitoring, operating and recording subsystem notifies the traffic system operator using an alarm or another method
when a traffic impediment is detected. The subsystem, using monitor TV, allows the operator to confirm both the situation and
the location of the impediment. The operator can then change the information provided to drivers as necessary, record the
situation with a VCR, or take action.
d
The notification subsystem provides information about the traffic impediments to drivers using variable message signs and
other means. Alternatively, it can forcibly close roads or prohibit traffic through certain roads.
Figure 1 — System configuration
2 © ISO 2001 – All rights reserved

3.2 Classifications
Table 1 presents a conceptual basis of the system. The table indicates that secondary accidents can be avoided
and drivers protected in the future because of the speedy detection and quick provision of information concerning
traffic impediments. Current standardization subjects are those indicated by “X” in the table.
NOTE The detection of congestion is not within the range of the systems addressed in this Technical Specification. TIWS
should detect stopped vehicles and/or slow moving vehicles at the tail of a congestion queue.
3.3 Objects constituting traffic impediments and detection coverage
3.3.1 Detection objects
3.3.1.1 Level 1: Stopped vehicles and slow moving vehicles, excluding motorcycles
3.3.1.2 Level 2: Level 1 + change in the movement of vehicles performed to avoid some obstacle or
hazardous condition that is present
3.3.1.3 Level 3: Level 2 + motorcycles
3.3.1.4 Level 4: Level 3 + other obstacles
NOTE 1 Level 1 is currently being considered as a subject for standardization.
NOTE 2 Limits of the size of detectable obstacles related to Level 4 are not addressed in this Technical Specification.
NOTE 3 Vehicle includes three-wheeled vehicles.
3.3.2 Detection coverage
The detection coverage in transverse directions shall include all traffic lanes and shoulders. The detection coverage
in longitudinal directions should be determined according to the sensor instrument performance, detection time,
installation height and peripheral environment (see annex D).
Table 1 — System concept for TIWS
Detection objects
Detection systems
Level 1 Level 2 Level 3 Level 4 Information providing
methods
a
Infrastructure Infrastructure- X Variable message sign
Class 1
system infrastructure
b
XVariable
Class 2
c
Cooperative Infrastructure- Beacon, leakage coaxial
Class 3
system vehicle cable, variable message,
sign, radio
NOTE Levels are defined in 3.3.
a
Necessary traffic information that has been collected by the infrastructure and reported to the traffic system
operator is provided to the travellers via variable message signs.
b
Information collected by the infrastructure is automatically provided to equipment (i.e. variable message signs)
which are installed in the infrastructure to improve the safe traffic flow of following vehicles. The information is also
reported to the traffic system operator.
c
Information collected by the infrastructure is automatically provided to devices installed in a vehicle (i.e. radio,
navigation display) by various communication methods (i.e. beacon, leakage coaxial cable), to avoid secondary
accidents. The information is also reported to the traffic system operator.
Figure 2 — Information providing flow with each class
3.4 Types of sensors
Various types of sensors are considered for use as shown in Figure 1. However, this Technical Specification
focuses on CCTV cameras that are used for image processing.
3.5 Provision of information
3.5.1 Required functions for providing information
3.5.1.1 Provision of information to drivers
The system has many ways, as shown in Figure 2, to provide drivers with information, however, this Technical
Specification focuses on variable message signs as the methods of provision.
4 © ISO 2001 – All rights reserved

3.5.1.2 Reporting to the traffic system operator
The occurrence of a traffic impediment shall be reported to the traffic system operator, who should be able to
monitor the CCTV screen to confirm the impediment.
3.5.2 Event detection
The system detects stopped, or slow moving vehicles.
3.5.3 Levels of information
The system provides two levels of information, primary, and secondary information. The timing and levels of
information are shown in Figure 3 (see annexes E and F).
t time when the event occurred
t time when the stopped vehicles or slow moving vehicles were detected
t time when the traffic system operator confirmed the type of event, condition, location of the occurrence and any response
action
Figure 3 — Levels of information
3.5.4 Types of information
Types of information can be classified as follows.
1) Instructions for action: Stop, limit speed, change lane.
2) Attention: Warning of a collision or a hazardous condition ahead.
3) Explanation of present situation: Type of impediment, route, location, traffic lane affected, any
response, or traffic control actions.
4) Forecast of situation: Forecast of travel time, time estimated to clear the impediment.
The types of information provided for each level are shown in Table 2.
3.5.5 Out-of-order indication
In case of system failure, words or a readily recognizable symbol shall be used to indicate that the system is not
able to provide traffic information.
Table 2 — Levels and types of information
Information types Message types Message examples Levels of information
Primary Secondary
Instruction Speed instruction Stop, slow down, … X
Route changing instruction Use alternative route X
Lane changing instruction Use right lane, left lane closed, … X
Attention Caution for a rear-end collision Stopped traffic ahead, slow XX
moving traffic ahead,
Caution to the hazardous condition Spilled load ahead, accident X
ahead ahead
Explanation of Route of occurrence Southbound Route 12 closed, … X
present situation
Location of occurrence Accident 250 m ahead … X
Traffic lane of occurrence One lane blocked, … X
Location of end of congestion queue End of congestion queue, ahead X
Traffic control Left lane closed, … X
Forecast Forecast of travel time About 20 min to XX, X
of situation 30 min delay, …
Estimated time of response action Closed for 1 h, X
3.6 Range of information provision to drivers
3.6.1 Locations for providing information
The locations where variable message signs are installed relative to the camera position, are as shown in Figure 4.
Key
1 Monitoring area X variable message sign installation interval
2 Occurrence of traffic impediment x camera blind spot distance
3 CCTV camera x out-of-sight distance
4 Variable message sign y judgement distance
5 Message sign recognition distance y reaction distance
y braking distance
Figure 4 — Locations where variable message signs are installed relative to camera position
6 © ISO 2001 – All rights reserved

The variable message sign should be installed a sufficient distance upstream from the CCTV camera so a vehicle
can stop before reaching a traffic impediment after having received information about it (see annex G).
The minimum value of the distance, X, between the variable message sign and the CCTV camera is given by the
following equation:
X =(y + y ) – (x + x ) (1)
2 3 1 2
where
x is the camera blind spot distance;
x is the out-of-sight distance;
X is the variable message sign installation interval;
y is the reaction distance;
y is the braking distance.
During actual operation, it would be desirable to alert drivers as early as possible by using additional information
equipment further upstream from the location of the variable message sign required by the above equation.
3.6.2 System reaction time (time from the occurrence of a traffic impediment until information is
provided), T
r
The system reaction time should be minimized, so when a traffic impediment occurs, the number of vehicles that
are unable to acquire necessary information is minimized. See Figure 5.
Key
1 Occurrence of traffic impediment L average vehicle spacing
s
2 CCTV camera T system reaction time
r
3 Variable message sign V velocity of traffic flow
Figure 5 — Image of system reaction time in terms of distance
The following relationship exists for the number of vehicles, n, that are unable to acquire traffic impediment
information (see annex H), if vehicles flow at the constant average spacing L .
s
n =(y + y + y + V� T)/ L (2)
1 2 3 r
s
thus,
T ={n� L – (y + y + y )} / V (3)
r 1 2 3
s
where
n is the number of vehicles unable to acquire traffic impediment information (vehicles/lane);
T is the system reaction time;
r
V is the velocityof trafficflow.
3.7 CCTV camera installation interval
Detection response time would be short at the point of a camera installed with a short interval, and long at the point
of a camera installed with a long interval, therefore providing information delay time would depend upon the
intervals of camera installation.
Quick detection response time should be requested at such poor visibility points as sharp curves, or in-tunnels,
and proper detection response time should be requested at good visibility points on straight roads.
CCTV installation interval should be defined by the concept that information provision delay time would be relative
to the location of information provision and monitoring area/points which would be specified according to CCTV
installation conditions and the road c
...