ISO/PRF TS 16951

TECHNICAL ISO/TS
SPECIFICATION 16951
Second edition
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
PROOF/ÉPREUVE
Reference number
ISO/TS 16951:2021(E)
ISO 2021
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ISO/TS 16951:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Data collection for the priority index procedure ............................................................................................................... 3

4.1 General ........................................................................................................................................................................................................... 3

4.2 Appoint an examiner ......................................................................................................................................................................... 3

4.3 Identify and assemble messages ............................................................................................................................................. 3

4.4 Define driving context and situation .................................................................................................................................... 3

4.4.1 Consider the sensing capability of the vehicle ....................................................................................... 3

4.4.2 Factors to consider in developing the driving scenarios ............................................................... 4

4.4.3 Document the driving context and situation ........................................................................................... 4

4.5 Select the evaluators .......................................................................................................................................................................... 5

4.6 Evaluate criticality and urgency of a message ............................................................................................................. 6

4.7 Instructions for the examiner .................................................................................................................................................... 6

4.8 Alternative method for determining message priority ........................................................................................ 7

5 Data analysis for priority index ............................................................................................................................................................ 8

5.1 General ........................................................................................................................................................................................................... 8

5.2 Select weights .......................................................................................................................................................................................... 8

5.3 Calculate priority, p ............................................................................................................................................................................

evaluators for each message ....................................................................................................................................................... 9

5.5 Calculate P and σ ..................................................................................................................................................................................

5.6 Determine priority order ............................................................................................................................................................... 9

5.7 Evaluate data quality ......................................................................................................................................................................10

6 Application of results ....................................................................................................................................................................................10

6.1 Prioritization of priority ranking .........................................................................................................................................10

6.2 How to deal with additional messages ............................................................................................................................10

6.3 Documentation ....................................................................................................................................................................................10

6.4 Other .............................................................................................................................................................................................................11

Annex A (normative) Priority matrix method .........................................................................................................................................12

Annex B (informative) System reaction matrix for priority matrix method ............................................................16

Annex C (informative) Rationale for recommended number of evaluatorsfor priority index

method .........................................................................................................................................................................................................................18

Annex D (informative) Example evaluator profile ..............................................................................................................................21

Annex E (informative) Driving scenarios ......................................................................................................................................................22

Annex F (informative) Criticality and urgency as the evaluation criteria ..................................................................25

Annex G (informative) Deriving weight k and k ..................................................................................................................................26

Annex H (informative) Sample report format ..........................................................................................................................................28

Annex I (informative) “Acceptable” standard deviations σ for priority indexes .................................................29

Bibliography .............................................................................................................................................................................................................................31

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This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 39,

This second edition cancels and replaces the first edition (ISO/TS 16951:2004), which has been

Any feedback or questions on this document should be directed to the user’s national standards body. A

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 document establishes two prioritization

methods for TICS and other system-initiated messages or driver-requested messages presented to

drivers while driving. Other prioritization methods are possible. The primary method given in this

document takes criticality and urgency ratings of such messages into consideration when calculating

a priority index. If the mathematical calculations are avoided for some reason, an alternative method

presented in Annex A is applied. The alternative method involves paired comparisons of all possible

messages to form a priority matrix. Its relative advantages and disadvantages are discussed in Annex A.

Annex B presents one way of managing messages using the priority obtained by Annex A.

Priority is one of the parameters to consider in determining when, where and how system messages are

displayed. As TICS applications are deployed, the number and frequency of TICS messages presented to

drivers can be expected to increase. This document 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 important messages reach the driver. This document complements ISO 15005 , a dialogue

This document 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

This document 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.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

EXAMPLE A message containing system status information, warnings or alarms presented using characters,

severity of the impact of the most likely accident or malfunction that can occur when the message is not

device that allows the presentation of visual, auditory, or haptic dynamic information to a driver

activities undertaken by the driver to navigate, manœuvre and handle the vehicle to achieve lateral and

person who judges the contents of a message from the point of view of criticality (3.2) and urgency

person who manages and conducts the use of this document for determining priority (3.10)

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 (3.4) and assisting them in driving safely and

relative importance of two or more messages which determines their ranking in a time sequence or

Note 1 to entry: The message with the highest priority is assigned first place (larger priority ratings correspond

index used to determine which messages should be given precedence when two or more messages are

explanation of the driving (3.4) context and situation for the message presented to evaluators (3.5)

message provided by a TICS (3.14) or conventional system (both inside and outside of the vehicle)

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

time within which driver action or decision is expected to be taken if the benefit intended by the system

This clause presents the steps for collecting the data used to calculate a priority index for each message.

The priority index procedure requires an examiner to coordinate the data preparation, analysis, and

The examiner shall be familiar with the prioritization process, knowledgeable on message management,

If the examiner has similar qualifications to that of the evaluators, the examiner may participate as

It is necessary for the examiner to identify in advance messages that are to be presented to drivers.

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

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

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

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-

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 4.4.2.

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

The following factors should be considered in developing the driving contexts and situations for

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

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).

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

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 2 Vehicle state: “driving speed”; “driving in left [right] lane”; “negotiating curve [intersection]”;

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

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 shall 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

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

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

Examiners shall ensure that evaluators understand the definitions of criticality and urgency, the two

evaluation criteria composing the priority index. For this, evaluators shall understand the four-category

ordinal evaluation scales used to assign criticality and urgency values (see Table 2 and Table 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 shall 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

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.

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 Table 2 and Table 3 to each evaluator (definitions of criticality and

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

d) explain the classification of criticality and urgency according to Table 2 and Table 3,

e) explain how to record the rating for criticality and urgency in the appropriate column of the

NOTE 1 Initially, three ratings scales were used in calculating a priority index. See Annex F for the reason for reducing the

NOTE 2 Only a few examples are shown above. These can be expected to vary in critica