ISO/TS 16951:2004

TECHNICAL ISO/TS
SPECIFICATION 16951
First edition
2004-03-15
Road vehicles — Ergonomic aspects of
transport information and control
systems (TICS) — Procedures for
determining priority of on-board
messages presented to drivers
Véhicules routiers — Aspects ergonomiques des systèmes de
commande et d'information du transport (TICS) — Modes opératoires
pour la détermination de la priorité des messages embarqués
présentés aux conducteurs
Reference number
©
ISO 2004
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ii © ISO 2004 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Terms and definitions. 1
3 Data collection for the priority index procedure.2
3.1 Appoint an examiner. 2
3.2 Identify and assemble messages . 3
3.3 Define driving context and situation. 3
3.4 Select the evaluators . 6
3.5 Evaluate criticality and urgency of a message . 6
3.6 Instructions for the examiner . 6
3.7 Alternative method for determining message priority . 8
4 Data analysis for priority index . 8
4.1 General. 8
4.2 Select weights . 8
4.3 Calculate priority p . 8
ij
4.4 Calculate arithmetic mean and standard deviation of priority index across evaluators for
each message. 9
4.5 Calculate P and σ . 9
j j
4.6 Determine priority order. 9
4.7 Evaluate data quality . 10
5 Application of results . 10
5.1 Prioritization of priority ranking . 10
5.2 How to deal with additional messages . 10
5.3 Documentation . 10
5.4 Other. 10
Annex A (normative) Priority matrix method. 11
Annex B (informative) System reaction matrix for priority matrix method . 15
Annex C (informative) Rationale for recommended number of evaluators for priority index method. 17
Annex D (informative) Example evaluator profile. 20
Annex E (informative) Driving scenarios . 21
Annex F (informative) Criticality and urgency as the evaluation criteria . 23
Annex G (informative) Deriving weight k and k . 24
c u
Annex H (informative) Sample report format . 25
Annex I (informative)  “Acceptable” standard deviations σ for priority indexes. 26
j
Bibliography . 28

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
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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.
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 after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
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/TS 16951 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 13,
Ergonomics applicable to road vehicles.
iv © ISO 2004 – All rights reserved

Introduction
When multiple in-vehicle information systems are present, including both transport information and control
systems (TICS) and non-TICS, various kinds of messages will be presented to drivers from these systems
and displayed at various times. If these messages are not managed properly, drivers could fail to obtain
critical information, which may degrade safety. This Technical Specification establishes two prioritization
methods for TICS and other system-initiated or driver-requested messages presented to drivers while driving.
Other prioritization methods are possible. The primary method given in this Technical Specification takes
criticality and urgency ratings of such messages into consideration when calculating a priority index. An
alternative method involving paired comparisons of all possible messages to form a priority matrix is
presented in Annex A and its relative advantages and disadvantages are discussed.
Priority is one of the parameters to consider in determining when, where and how system messages are to be
displayed. As TICS applications are deployed, the number and frequency of TICS messages presented to
drivers can be expected to increase. This Technical Specification will provide road vehicle manufacturers and
TICS suppliers with a consistent basis for the management of messages competing for the driver’s limited
information processing capability. This, in turn, will reduce the driver’s workload and help ensure that the most
[3]
important messages reach the driver. This Technical Specification complements ISO 15005 , a dialogue
management standard.
This Technical Specification is intended for those involved in the design of message management systems
that integrate in-vehicle messages. It describes how to establish message priorities. It also specifies criteria
for message prioritization and, therefore, serves as an evaluation tool for TICS installed in vehicles as
standard equipment and for after-market TICS devices.

TECHNICAL SPECIFICATION ISO/TS 16951:2004(E)

Road vehicles — Ergonomic aspects of transport information
and control systems (TICS) — Procedures for determining
priority of on-board messages presented to drivers
1 Scope
This Technical Specification provides formal procedures and two, alternative, methods (users are advised to
choose whichever of the two suits their individual requirements) for determining the priority of on-board
messages presented to drivers of road vehicles by transport information and control systems (TICS) and other
systems. It is applicable to the whole range of TICS in-vehicle messages, including traveller information,
navigation, travel and traffic advisories, “yellow pages” information, warnings, systems status, emergency
calling system information, and electronic toll/fee collection, as well as to messages from non-TICS sources
such as telephone, warnings and telltales. Although applicable to systems that allow the free generation of
messages, it neither provides guidance on how to use the messages deriving from its procedures nor is it
applicable to mandatory or legally required messages.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
contents of message
information presented to a user by the TICS or other on-board system
EXAMPLE A message containing system status information, warnings or alarms presented using characters,
symbols, figures, audible tones, voices or other means.
2.2
criticality
severity of the impact of the most likely accident or malfunction that can occur when the message is not
received or is ignored by the driver
2.3
display
device that allows the presentation of visual, auditory, or haptic dynamic information to a driver
2.4
driving
activities undertaken by the driver to navigate, manœuvre and handle the vehicle to achieve lateral and
longitudinal control
2.5
evaluator
person who judges the contents of a message from the point of view of criticality and urgency to the driver
2.6
examiner
person who manages and conducts the use of this Technical Specification for determining priority
2.7
k
c
weighting of criticality used to calculate the priority index
2.8
k
u
weighting of urgency used to calculate the priority index
2.9
message management system
system that controls and evaluates a wide range of information and presents it ergonomically to drivers,
allowing them to cope with the information while driving and assisting them in driving safely and comfortably
2.10
priority
relative importance of two or more messages which determines their ranking in a time sequence or emphasis
of presentation
NOTE The message with the highest priority is assigned first place (larger priority ratings correspond to higher
priority items).
2.11
priority index
index used to determine which messages should be given precedence when two or more messages are
available for presentation
2.12
scenario
explanation of the driving context and situation for the message presented to evaluators
2.13
system-initiated message
message provided by a TICS or conventional system (both inside and outside of the vehicle) without a specific
request from the driver
2.14
transport information and control system
TICS
system comprised of an advanced information and telecommunications network for users, roads and vehicles
that contributes to solving problems such as traffic accidents and congestion
[4]
NOTE See ISO/TR 14813-1 for a list of TICS services .
2.15
urgency
time within which driver action or decision has to be taken if the benefit intended by the system is to be
derived from the message
3 Data collection for the priority index procedure
This clause presents the steps for collecting the data used to calculate a priority index for each message. See
the example outputs given in Annex E and Annex H.
3.1 Appoint an examiner
The priority index procedure requires an examiner to coordinate the data preparation, analysis, and reporting.
The role of the examiner is detailed in 3.6.
2 © ISO 2004 – All rights reserved

The examiner shall be familiar with the prioritization process, knowledgeable on message management, and
have automotive experience.
If the examiner has similar qualifications to that of the evaluators, the examiner may participate as both an
examiner and evaluator.
3.2 Identify and assemble messages
It is necessary for the examiner to identify in advance messages that are to be presented to drivers. Generally
speaking, the messages represent the aggregate output given by the TICS and non-TICS connected to a
message management system. The examiner shall collect these messages and prepare them for presentation
to the evaluators.
3.3 Define driving context and situation
For each message, the examiner shall define, or assist in defining, a driving context and situation in terms of
the road environment and the traffic condition in which the message is likely to be presented.
The contextual and situational factors should be defined at the moment when the message is presented
because the priority (assignment of criticality and urgency ratings) depends heavily on the driving context.
Particular attention should be given to the presentation of messages in potentially hazardous situations. All
hazardous situations should be considered, except for highly unlikely possibilities. Based on these situations
the examiner may define one or more (normally not more than four) scenarios for a particular message.
The same message in two different scenarios shall be regarded as two different information items to be
evaluated. This is because messages may occur in several different driving contexts, and each context could
yield a different message priority. For example, the priority given to a message pertaining to a system
malfunction will be different depending on whether the driver is starting the car or is relying on the system
whilst driving.
If only one scenario is used for a given message, that scenario should represent a reasonable “worst-case”
situation. At minimum, a TICS or non-TICS expert and the examiner should agree on the worst-case driving
scenario. A traffic safety expert may also be consulted.
3.3.1 Consider the sensing capability of the vehicle
In practice the messages that are provided to the driver will depend on the capability of the vehicle to sense or
detect various relevant situations. For example, if the vehicle can detect the driver’s state of arousal, then the
driver’s state can be considered in describing the driving scenario.
For situations in which the vehicle is incapable of sensing, the message priority should be determined for a
scenario representing a “reasonable” worst-case situation for the factors listed in 3.3.2.
3.3.2 Factors to consider in developing the driving scenarios (see Table 1)
Table 1 is provided to assist the examiner in developing driving context and relevant situations. A sample of
situation and context factors is given in the rightmost column. The examiner may use these or other factors to
define driving scenarios. If the context cannot be categorized into one of the candidate factors listed in Table 1,
it should be clearly described within the “Other” parentheses. If neither the context nor situation is defined for
one of the factors, select “not defined (N-D)” from the list of the candidates.
The following factors should be considered in developing the driving contexts and situations for evaluators to
consider when making their ratings.
3.3.2.1 Trip context
The trip context is a factor that considers the aim of the trip (e.g. commuting, leisure), the timing or position
along the route (e.g. relative position between start and destination), and the preparatory distance to the next
manœuvre.
EXAMPLE “Close (e.g. 20 m) to turn (or merge)”.
3.3.2.2 Road environment
The road environment is a static factor related to road structure that affects driving. Considerations shall
include the road type (e.g. highway, urban road, country road), the speed limit, the number of lanes, and the
road width. Consideration shall also be given to the effect on driving of the surrounding environment, including
weather conditions and time of day (e.g. morning, daytime, night time, raining).
3.3.2.3 Traffic situation
The traffic situation is a dynamically changing factor related to traffic or obstacles on the road that affect
driving. Considerations here include the relationship to other vehicles, such as headway distance and speed
difference to the lead vehicle.
EXAMPLE 1 “Headway distance”.
EXAMPLE 2 “Lateral vehicle exists”.
EXAMPLE 3 “Speed difference to the lead vehicle”.
3.3.2.4 Vehicle condition
This factor originates from the vehicle itself and derives from the relationship between the vehicle and the road.
Vehicle condition can be separated into “vehicle type” and “vehicle state”.
EXAMPLE 1 Vehicle type: “passenger vehicle”, “heavy vehicle”.
EXAMPLE 2 Vehicle state: “driving speed”; “driving in left [right] lane”; “negotiating curve [intersection]”; position of the
vehicle within a lane.
3.3.3 Document the driving context and situation
The defined driving context, situation, appropriate driver behaviours and/or cognitive demands associated with
each message shall be documented. An example for a specific configuration is given in Annex E.
4 © ISO 2004 – All rights reserved

Table 1 — Factors to consider in developing driving scenarios
Driving context/situation Candidate situational or contextual factors
Close to turn (or merge, or diverge)
Trip context Other (……)
N-D
Highway / urban / country / curve / icy / wet
Speed limit (…)
Road Number of lanes (…)
Other (……)
Road environment: N-D
Rain / fog
Time of day (morning / daytime / night-time)
Weather
Other (……)
N-D
Headway distance is approx. (…) m or (…) s
Lateral vehicle(s) exists (yes or no)
Traffic situation
Speed difference to the lead vehicle is approx. (…) km / h
N-D
Passenger vehicle / heavy vehicle
Type Other (……)
N-D
Driving speed (…) km/h (mph)
Driving in left (or right) lane
Status on roadway /
Curve (intersection) negotiation
manœuvre
Vehicle condition
Other (……)
N-D
Systems check after start-up shows all systems are normal
Malfunction of system (……) — provide relevant details
Status of vehicle
subsystem(s)
Other (……)
N-D
Driver’s state of arousal
Miscellaneous
N-D
N-D Not defined.
3.4 Select the evaluators
The examiner shall select a minimum of 5 evaluators (see 4.1 and Annex C).
Evaluators should include experienced human factors and road safety practitioners and others who possess a
good understanding of the functions of the subject TICS system. They must be well-informed of the traffic
environment and road environment of the subject country/region and have the ability to evaluate and take into
account the safe presentation of messages. Actual use of the system is recommended for all evaluators.
The profile of each evaluator should be recorded. Profiles should include field of expertise, knowledge of road
safety, human factors, and knowledge of the systems producing messages that are prioritized (see Annex D).
3.5 Evaluate criticality and urgency of a message
The contents of messages and the driving scenarios shall be explained by the examiner so that the evaluators
have a common understanding of the scenario, the functions of the system, and the contents of messages
being examined.
Examiners shall ensure that evaluators understand the definitions of criticality and urgency, the two evaluation
criteria composing the priority index. For this, evaluators must understand the four-category ordinal evaluation
scales used to assign criticality and urgency values (see Tables 2 and 3).
Each evaluator shall assign a criticality and urgency rating for each message assuming he/she is the driver.
In general, urgency will be time dependent. Controllability is one of the important factors that must be
considered in determining urgency. If the situation is uncontrollable, no action shall be expected from drivers.
However, if there is a possibility of controlling the situation, then urgency shall be determined depending on
[2]
when the system expects drivers to take an action to handle it .
If the examiner has not fully defined the driving context and situation, evaluators shall be instructed to
consider all hazardous situations, except for highly unlikely possibilities. They should assume a reasonable
worst-case scenario when determining their criticality and urgency ratings.
3.6 Instructions for the examiner
The role of the examiner is to
a) record information about each evaluator in the evaluator profile (see Annex D),
b) create the questionnaire according to Annex E for the vehicle and system to be evaluated, and distribute
the questionnaire and Tables 2 and 3 to each evaluator (definitions of criticality and urgency should be
provided with the questionnaire),
c) explain the evaluation items and the contents of the message(s) in the questionnaire, while providing a
means for evaluators to record the driving context and situation they used in making their evaluations,
whenever the examiner’s description was not clear or sufficient,
d) explain the classification of criticality and urgency according to Tables 2 and 3,
e) explain how to record the rating for criticality and urgency in the appropriate column of the questionnaire,
f) collect the questionnaire, and
g) analyse the data and report the results.
6 © ISO 2004 – All rights reserved

Table 2 — Criticality rating scale
Risk to vehicle,
Rating occupants and/or Examples
pedestrians
Ignoring speed warning when driving significantly above the speed limit.
Collision as a result of loss of braking due to ignoring the brake failure warning.
Departing roadway due to ignoring lane departure warning.
3 Severe or fatal injury
Collision at high speed.
Leaving the roadway, head-on collision and collision with structures at intermediate
speed.
Following vehicle ahead too closely at high speed.
Risk of collision due to following a vehicle ahead too closely at intermediate speed.
Vehicle(side)-to-vehicle(side) collision due to ignoring collision warning at
2 Injury or possible injury
intermediate or low speed, vehicle leaving the road, head-on collision and collision
with structures at intermediate or low speed.
Vehicle-to-vehicle collision except head-on collision at low speed.
No injury (vehicle
1 Following vehicle ahead too closely at low speed.
damaged)
Collision with structures at low speed.
Vehicle-to-vehicle contact at very low speed.
No injury (no vehicle
damage)
Collision with structures at very low speed.
NOTE 1 Initially, three ratings scales were used in calculating a priority index. See Annex F for the reason for reducing the number
of rating scales to two.
NOTE 2 Only a few examples are shown above. These can be expected to vary in criticality from region to region depending on the
road environment and other situational and contextual factors. Therefore, examiners are able to alter them at their discretion.
NOTE 3 The examples shown here illustrate that a warning message can be assigned a high criticality rating, even if failure to
respond to the warning does not result in a crash.
NOTE 4 Driving speeds vary by country. The speed values (km/h) for “very low”, “low,” “intermediate”, and “high” speed will
depend on the country and on elements of the driving scenario such as urban, suburban, or expressway roads.
Table 3 — Urgency rating scale
Rating Description Examples
Obstacle immediately in the vehicle path. Brake
Respond immediately
immediately. Steer to avoid dangerous situations.
3 Take immediate action or decision (within zero to three
seconds) according to the displayed information.
ACC malfunctioning.
Respond within a few seconds Obstacle within a few seconds in the vehicle path.
Take action or decision according to the information
2 Brake in a few seconds. Steer away from danger as
[1]
required.
within 3 to 10 seconds .
Response preparation
Prepare to take action or decision according to the Onset of detection of an obstacle.
information within 10 seconds to 2 minutes.
Information only
System on.
No direct action or decision required by driver
3.7 Alternative method for determining message priority
An alternative method for determining message priority, the priority matrix method, is given in Annex A. This
method determines priority subjectively by having subject matter experts make pair-wise comparisons of all
messages. It involves neither the steps of rating criticality and urgency based on Tables 2 and 3 nor the
calculation of a priority index according to Clause 4.
4 Data analysis for priority index
4.1 General
This clause provides a method for calculating the message priority index based on evaluator ratings of
criticality (c ) and urgency (u ).
i i
Since the priority index for each message is obtained by averaging the priority indexes of each evaluator, the
number of evaluators affects the reliability of the overall index. Therefore, ten or more evaluators are
recommended in order to make the priority index reliable (See Annex C). However, fewer than ten evaluators
1)
are acceptable if the standard deviation across evaluators is small enough . Annex I contains an example
procedure for determining acceptable standard deviations. In all cases, the minimum number of evaluators
should be five, to avoid bias by the selection of evaluators.
4.2 Select weights
In order to use this Technical Specification, those involved in the design of the message management system
need numerical values of k and k as the first step. When there is no established rule to determine k and k ,
c u c u
one way is to assign 1,0 to k and k making criticality and urgency equally important. Another way is to obtain
c u,
k and k based on empirical data. An example of the method is shown in Annex G. This example indicates
u c
that k = k = 1 can be used as rounded values for the weight factors. The evaluator’s ratings of criticality (c )
u c i
and urgency (u ) given in Clause 3 are used to calculate priority index P in 4.4 [see Equation (2)]. As the
i j
ratings range between 0 and 3 for both criticality and urgency (see Tables 2 and 3), k = k = 1 means that the
c u
contribution of criticality and urgency to the priority index would be the same.
4.3 Calculate priority p
ij
Priority p indicates the relative importance of the ith evaluator and jth message and is calculated according to
ij
the following Equation (1).
p = k c + k u (1)
ij c ij u ij
where
p is the individual value for priority index;
ij
c , u are the individual scores, respectively, of criticality and urgency;
ij ij
k , k are weight factors respectively of criticality and urgency against p (see 4.2).
c u i
1) The definition of “small enough” variance is still being investigated.
8 © ISO 2004 – All rights reserved

4.4 Calculate arithmetic mean and standard deviation of priority index across evaluators for
each message
The arithmetic mean P , given by Equation (2), is the priority index, which indicates the relative importance of
j
the jth message:
n
Pp= n
ji∑j
i=1
n
=+kc k u n (2)
()
cij u ij
∑
i=1
=+kC kU
cj u j
where
P is the priority index of the jth message;
j
C , U are the mean score across evaluators, respectively, of criticality and urgency of the jth message;
j j
n is the number of evaluators.
Standard deviation σ , given by Equation (3), indicates the relative confidence of the priority index of the jth
j
message.
n
σ==Vp−Pn
()
jj ∑ij j
i=1
nn

=−ppn n (3)
∑∑ij ij

ii==11
nn

=+kc k u− kc+k u n n
()( )
cij u ij cij u ij
∑∑

==11
ii
where
σ is the standard deviation of the jth message;
j
V is the variance of the priority index of the jth message.
j
4.5 Calculate P and σ
j j
Repeat Equations (2) and (3), calculating P and σ for each of the j messages.
j j
4.6 Determine priority order
Rank the messages in terms of their P values; then list the messages in descending order (larger values
j
correspond to higher priority items). When items have the same numerical P values, priority should go to the
j
message whose mean criticality score C is higher.
i
Prepare a priority order table that lists the numerical values C and U , and P and σ, for each message
j j j j
evaluated.
An empty table for displaying an example of a priority index calculated by assigning 1,0 to k and k is shown
u c
in Annex H.
4.7 Evaluate data quality
For the evaluators’ priority ratings of each message, verify that a sufficient level of agreement among
evaluators was achieved to ensure sufficiently high data quality. This can be done using either of two different
methods. The agreement is sufficient if:
a) more than half the number of evaluators agree on the criticality and urgency ratings of a message, or
b) the standard deviation of priority index is less than 1,0 (see Annex I).
If neither was the case, the examiners shall interview the evaluators to ask if the explanation of message
context was ambiguous. If so, the examiners shall clarify or provide additional details of the driving context
and situation to the evaluators, and the evaluators shall re-evaluate the messages.
NOTE In cases where re-evaluation takes place, messages that in the first evaluation achieved an average criticality
of less than 0,5 and an average urgency of less than 1,5 need not be considered in the re-evaluation.
5 Application of results
5.1 Prioritization of priority ranking
As a general principle, designers should use the priority rankings to avoid the simultaneous presentation of
messages. This is particularly important with auditory messages. If two or more in-vehicle messages need to
be displayed to the driver at the same time, those with larger priority rankings should be emphasized. After the
message(s) has been presented to the driver, the driver should be in control of selecting, deactivating, and
cancelling messages, independent of priority, except for messages regulated by law.
Even if the process for determining a priority index is performed adequately in accordance with Clauses 3 to 5,
it can sometimes happen that the standard deviation of one message is extremely large compared with those
of other messages. This might be caused by differences in evaluators’ understanding of the criticality and
urgency of messages. Therefore, due attention should be paid to handling such messages by, for example,
devising special means of message presentation.
5.2 How to deal with additional messages
When new TICS systems or messages are developed, it is necessary to establish the priority for such new
messages. If any evaluator is replaced with a new evaluator, he/she should be selected from a similar
discipline as the previous evaluator (see 3.3).
The procedures according to 3.2 to 4.5 shall be performed only when additional messages are added. The
values obtained by these procedures shall be put into the appropriate position of the priority order table
already obtained according to 4.6 to determine the priority orders of the new messages.
5.3 Documentation
The examiner shall issue a report containing the following topics:
a) evaluators’ profiles (see Annex D);
b) list of messages with driving situations (see Annex E) and consequences if a message is ignored;
c) priority index of each message (see Annex H).
5.4 Other
The installed priority ranking should be communicated to the driver by appropriate means (e.g. operator’s
manual).
10 © ISO 2004 – All rights reserved

Annex A
(normative)
Priority matrix method
A.1 Overview of method
The priority matrix is an alternative method for determining priority when there are competing TICS and non-
TICS messages. It can be used in lieu of the method according to Clauses 3, 4 and 5. The basic idea is to
avoid the mathematical formulation of an abstract criterion (index) based on criticality and urgency and instead
list all the messages that will be presented to the driver in a matrix format with n (i.e. number of all the
messages) columns and rows. Messages are formulated exactly as they would be displayed in the vehicle.
Each message should clearly describe the behaviour or malfunction of the system. Experts then compare
each pair of messages, and the message with higher priority is recorded. The procedure is repeated until all
possible pairs of messages are compared.
A.2 Advantages and disadvantages of method
This method has been chosen because it fits well into the engineering process of the human-machine
interface (HMI) development.
a) Main advantages
 The method can be performed with the existing experts for the respective systems, there being no need
to involve persons with an in-depth knowledge of all warning messages in the car (who could be hard to
find, even in an automotive company).
 Optimisation of system reaction is rather easy (see Annex B), with any necessary adjustment able to be
done in the respective cell without influencing any other parts of the system.
b) Main disadvantages
 All possible pairs of messages should be evaluated, which can result in a large number of evaluations.
 System reactions based on the priority matrix require more device memory space to implement.
A.3 Requirements for examiner and evaluators
A.3.1 Examiner
The examiner shall be expert in the TICS systems being evaluated and have HMI experience, or shall be an
HMI expert with a good understanding of the TICS systems being evaluated. The examiner shall also be
familiar with the prioritization process, knowledgeable on message management, and have automotive
experience. The role of the examiner is detailed in A.5.
A.3.2 Expert evaluators
Evaluators shall be selected from experts (specialists) of the respective TICS and non-TICS systems. HMI
experts may also serve as evaluators. At minimum there should be one such expert evaluator representing
each TICS.
The expert evaluator should possess a good understanding of the functions of the subject TICS or non-TICS
system, be well informed of the traffic environment and road environment of the subject country/region, and
have the ability to evaluate and take into account the safe presentation of messages. Actual use of the system
is recommended for all expert evaluators.
The profile of each expert evaluator should be recorded. Profiles should include: age, gender, expertise,
experience in terms of years in his or her field of expertise, and experience in terms of years in the study of
TICS human interfaces (see Annex D).
A.3.2.1 Expert opinion
The expert evaluator determines the priority for each individual message on the basis of his or her good
knowledge of the system or of all the messages that can be displayed.
Criticality and urgency are considerations to be discussed when making the priority judgment for each pair of
messages. The criteria of criticality and urgency are implicitly included in every priority decision. There is no
need to explicitly rate criticality and urgency in order to determine priority, as is done in the priority index
method.
A.4 Procedure
A.4.1 Identify and assemble messages
The examiner shall collect in advance messages that are to be presented to drivers. Generally speaking, the
messages represent the aggregate output given by the TICS and non-TICS systems connected to the
message management system. The examiner shall prepare the priority matrix for presentation to the expert
evaluators. All the messages that can be displayed are entered into the matrix, with each message appearing
in a column and in a row (see Table A.1).
A.4.2 Define driving context and situation
For each message, the examiner shall define, or assist in defining, a driving context and situation in terms of
the road environment and the traffic condition in which the message is likely to be presented. This definition
serves two purposes. It clarifies the driving context and it distinguishes between different situations, when
those situations could influence the message priority and/or the system reaction.
A.4.2.1 Clarify driving context
Driving context and situation can be classified into “trip context”, “road environment”, “traffic situation”, and
“vehicle condition” (see 3.3.2). For each message, these contextual and situational factors should be defined
at the moment when the message is presented because the priority depends heavily on the driving context.
Particular attention should be given to the presentation of messages in potentially hazardous situations. All
hazardous situations should be considered, except for highly unlikely possibilities. Based on these situations
the examiner may define one or more (normally not more than four) scenarios for a particular message.
If only one scenario is used for a given message, that scenario should represent a reasonable “worst-case”
situation. At minimum, a TICS or non-TICS expert and the examiner should agree on the worst-case driving
scenario. A traffic safety expert may also be consulted.
A.4.2.2 Differentiate between situations
Messages occur in several different driving contexts, and in some cases each context yields a different
message priority. For example, the priority given to a message pertaining to a system malfunction will be
different depending on whether the driver is starting the car or is relying on the system whilst driving. This
requires that the different scenarios be distinguishable by in-vehicle sensors.
In those situations, the same message in two different scenarios shall be regarded as two different information
items to be evaluated. Each scenario will have a separate row and column in the priority matrix.
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A.4.2.3 Document the driving context and situation
The defined driving context, situation, appropriate driver behaviours, consequences if the message is ignored
and/or cognitive demands associated with each message shall be documented (see 3.3 and Table 1). An
example for a specific configuration is given in Annex E.
A.4.3 Evaluate the priority of messages
The contents of messages and the driving scenarios shall be explained so that the expert evaluators have a
common understanding of the scenario, the functions of the system, and the contents of messages being
examined.
The expert evaluators shall understand the definitions of criticality (2.2) and urgency (2.15).
The expert evaluator assesses and records the priority of the row message compared with the column
message for each cell of the matrix. (A cell is the point of intersection of two messages from a column and a
row. See Table A.1.)
When determining priority for messages coming from two different TICS or non-TICS systems, the relative
priority between two messages is obtained by the agreement of the expert evaluators from the respective
TICS or non-TICS systems. In some cases, the same person may be responsible for, or may have in-depth
knowledge of, both applications and can do the comparison alone. If no agreement is reached, the topic is
discussed under the supervision of the examiner, an HMI expert. If no agreement is yet reached, the priority is
decided by the vote of the two expert evaluators and the examiner.
An example of a priority matrix is shown in Table A.1. The ex
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