ISO 16673:2017
(Main)Road vehicles — Ergonomic aspects of transport information and control systems — Occlusion method to assess visual demand due to the use of in-vehicle systems
Road vehicles — Ergonomic aspects of transport information and control systems — Occlusion method to assess visual demand due to the use of in-vehicle systems
ISO 16673:2017 provides a procedure for measuring visual demand due to the use of visual or visual-manual interfaces accessible to the driver while the vehicle is in motion. It applies to both original equipment manufacturer (OEM) and after-market in-vehicle systems. It applies to both permanently installed and portable systems. It applies to any means of visual occlusion and is not dependent on one specific physical implementation.
Véhicules routiers — Aspects ergonomiques des systèmes d'information et de contrôle du transport — Méthode par occlusion pour évaluer la distraction visuelle due à l'utilisation des systèmes embarqués
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INTERNATIONAL ISO
STANDARD 16673
Second edition
2017-09
Road vehicles — Ergonomic aspects
of transport information and control
systems — Occlusion method to assess
visual demand due to the use of in-
vehicle systems
Véhicules routiers — Aspects ergonomiques des systèmes
d'information et de contrôle du transport — Méthode par occlusion
pour évaluer la distraction visuelle due à l'utilisation des systèmes
embarqués
Reference number
ISO 16673:2017(E)
©
ISO 2017
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ISO 16673:2017(E)
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ISO 16673:2017(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Measurement procedures . 4
4.1 Set-up . 4
4.2 Vision and occlusion intervals . 4
4.3 Task timing . 5
4.4 Exclusion of trials . 6
5 Assessing visual demand . 6
5.1 Selection of tasks . 6
5.2 Participants . 6
5.3 Training . 6
5.4 Test trials . 7
5.5 Experimental plan . 7
5.6 Calculation of visual demand metrics . 8
5.6.1 General. 8
5.6.2 Calculating TSOT . 8
5.6.3 Calculating R . 9
5.6.4 Interpretation of results .10
Annex A (informative) System response delay .11
Annex B (informative) Surrogate driving task as a primary task .14
Bibliography .15
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ISO 16673:2017(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
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electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
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expressions related to conformity assessment, as well as information about ISO's adherence to the
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URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 39,
Ergonomics.
This second edition cancels and replaces the first edition (ISO 16673:2007), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the accessibility has been changed from “unrestrained driver” to “buckled driver” in 3.1;
— the following paragraph has been added in 4.1: “Written instructions should not be visible to the
participants during task performance or they should be visible to the participants during the whole
task performance, i.e. also during occluded intervals”;
— Annex B has been added.
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ISO 16673:2017(E)
Introduction
A wide range of information and communication devices and advanced driver assistance systems are
being introduced into motor vehicles. These include navigation aids, emergency messaging systems and
wireless communication including email and internet access, which are all accessible to the driver of
a motor vehicle. Many of these features have associated visual information that can potentially both
inform and distract. To help ensure that the use of such devices and features that are meant to be
used by the driver while driving do not result in excessive visual demand, a consistent, verifiable and
repeatable method to determine the visual demand imposed by such in-vehicle systems is needed.
Developing precise mathematical predictions of the risk of a crash due to driver distraction from
using a particular driver interface is difficult. However, it can be reasonably stated that if drivers are
not looking at the road (e.g. looking inside the vehicle to operate a control or read a display), then the
[5]
probability of a crash is increased .
This document is not intended to preclude direct measurement of eye glances as a method to assess
visual demand. Direct measurement of eye glances is always desirable. However, direct measurements
of eyes-off-the-road times, i.e. glance time measurements, are typically difficult and very costly to
measure. The occlusion method estimates visual demand, including resumability, of a task using a
means for intermittent viewing of the in-vehicle system. Evaluation by occlusion identifies driver
interfaces that are likely to take the driver’s eyes away from the road for excessively long durations.
Additional data collected without occlusion can be combined with occlusion data to calculate R, a
measure believed to identify whether or not tasks can be easily resumed after the driver interrupts the
task to look back at the road. This procedure does not require extensive resources and can be applied if
a functioning prototype of the driver interface exists.
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INTERNATIONAL STANDARD ISO 16673:2017(E)
Road vehicles — Ergonomic aspects of transport
information and control systems — Occlusion method to
assess visual demand due to the use of in-vehicle systems
1 Scope
This document provides a procedure for measuring visual demand due to the use of visual or visual-
manual interfaces accessible to the driver while the vehicle is in motion. It applies to both original
equipment manufacturer (OEM) and after-market in-vehicle systems. It applies to both permanently
installed and portable systems. It applies to any means of visual occlusion and is not dependent on one
specific physical implementation.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1
driver accessible
interface controls necessary to complete the task (3.11) that are within the reach of the buckled driver
and the interface display is visible with a head movement, and the system is operable by the driver
[1] [3]
Note 1 to entry: See ISO 3958 for the driver reach of the restrained driver, and SAE J1050 for the head
movement.
Note 2 to entry: The driver interface includes the visual display and any relevant controls.
EXAMPLE A nomadic or portable device such as a PDA outside of the reach of a restrained driver is still
considered driver accessible if within the reach envelope of a buckled driver.
3.2
glance duration
time from the moment at which the direction of gaze moves towards a target (e.g. the interface display)
to the moment it moves away from the target
Note 1 to entry: This includes the transition time to that target as shown in Figure 1, simplified from
[2]
ISO 15007-1:2014, Figure A.2 .
Note 2 to entry: A single glance duration may also be referred to as a glance.
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ISO 16673:2017(E)
Key
X time
1 target B (e.g. the interior mirror)
2 target A (e.g. the roadway)
3 target C (e.g. in-vehicle display)
a
Glance duration.
Figure 1 — Chronological relationship of driver visual allocation between target regions
3.3
goal
system end state sought by the driver and which is meaningful in the context of a driver’s use of an in-
vehicle system
EXAMPLE Obtaining guidance to a particular destination, magnifying a map display, or cancelling route
guidance.
3.4
integrated system
two or more in-vehicle devices which provide information to, or receive output from, the driver of a
motor vehicle whose input and/or output have been combined or harmonized
EXAMPLE 1 An in-vehicle entertainment system and route guidance system which use the same visual and
manual input portals and visual and auditory output portals.
EXAMPLE 2 An in-vehicle entertainment system whose auditory output mutes when a mobile phone call is
made or received.
3.5
occlusion interval
time during which the driver interface is not visible when using an occlusion procedure
3.6
outlier
[6]
observation that lies outside the overall pattern of the sample data distribution
3.7
portable system
device, which provides information to, or receives output from the driver of a motor vehicle, that can be
used within the vehicle without installation or can be rapidly and easily installed in and removed from
a vehicle
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ISO 16673:2017(E)
3.8
resumability
ease with which a dialogue can be continued after it is interrupted
Note 1 to entry: A dialogue is considered resumable if task performance continues without a significant
degradation after an interruption.
3.9
resumability ratio
R
ratio of the duration of the total shutter open time (TSOT) to the total task time unoccluded (TTT ),
Unoccl
i.e. TSOT/TTT
Unoccl
3.10
system response delay
SRD
interval during which the driver has to wait for an interface to respond or update in order to
continue a task
EXAMPLE Waiting for an off-board computer to be queried or waiting for a voice message to be generated.
3.11
task
process of achieving a specific and measurable goal using a prescribed method
Note 1 to entry: Ultimately, it is for the users of this document to determine tasks that are meaningful in the
context of a driver’s use of a system.
EXAMPLE 1 Obtaining guidance by entering a street address using the scrolling list method, continuing until
route guidance is initiated (visual-manual task).
EXAMPLE 2 Determining where to turn based on a turn-by-turn guidance screen (visual task).
3.12
total shutter open time
TSOT
total time that vision is not occluded when using an occlusion procedure (3.19)
Note 1 to entry: TSOT is the sum of vision intervals (3.17) required for the task (3.11) of interest.
3.13
total task time occluded
TTT
Occl
total time to complete the task (3.11) of interest, including both unoccluded and occluded intervals,
while using a visual occlusion procedure (3.19)
3.14
total task time unoccluded
TTT
Unoccl
total time required to complete the task (3.11) of interest without using a visual occlusion procedure
(3.19) and without any concurrent task
3.15
trial
investigation of one participant undertaking one repetition of one task (3.11)
3.16
vehicle in motion
vehicle whose speed relative to its supporting surface is “nonzero”
Note 1 to entry: Practical limitations on existing vehicle sensors may cause small velocities (typically not more
than 5 km/h) to be registered as zero.
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ISO 16673:2017(E)
3.17
vision interval
discrete time during which the driver interface is visible when using an occlusion procedure
Note 1 to entry: Vision interval is also the shutter open time (SOT).
3.18
visual demand
amount of visual activity required to extract information from an interface of an in-vehicle system to
perform a specific task (3.11)
Note 1 to entry: In general, visual demand depends on the quantity of information to be extracted and the ease
with which information extraction can be resumed following any interruption.
3.19
visual occlusion procedure
measurement method involving periodic obstruction of the participant’s vision or the obscuration of
visual information under investigation
4 Measurement procedures
4.1 Set-up
Intermittent viewing of an interface can be provided by various means. The occlusion procedure
approximates the driver looking back and forth between the forward driving scene and an in-vehicle
[8]
interface, looking at each for a brief period of time. In addition to the commonly used goggles ,
occlusion can be achieved using blanking of the visual display or a shutter in front of the interface.
Display blanking can be done by electronically turning the visual display on and off in accordance
with the timing in 4.2. A shutter shall be opaque during the occlusion interval. This could be done
electronically with a variable transmittance lens, such as that used in the occlusion goggles, or it could
be done using a system of one or more mechanical shutters. In the latter case, the shutters should not
interfere with operation of the manual controls. Whether using electronic or mechanical means, the
switching process and restoration of the active screen display at the end of an occlusion interval shall
occur in less than 20 ms. Early studies involving occlusion in the primary driving task (forward field of
[17]
view) used a head mounted mechanical shutter .
During the occlusion interval, neither the interface displays nor controls shall be visible, but operation
of the controls shall be permitted (though most input to the interface might occur when vision is
available). This protocol simulates drivers looking at the road but continuing to enter information via a
manual control.
The system under investigation shall be operational and fitted to a vehicle, simulator buck, or mock-up
in a design which duplicates the intended location of the interface in the vehicle (i.e. the viewing angle
and control placement relationships shall be maintained). The ocular illumination levels in the vision
and occlusion intervals should be comparable so that dark/light adaptation of the participants’ eyes is
not necessary during the procedure.
The instruction shall be standardized and be presented either orally or in writing. The display and
controls of the interface should be visible during instruction. An instruction may be repeated at the
request of the participant.
Written instructions should not be visible to the participants during task performance or they should
be visible to the participants during the whole task performance, i.e. also during occluded intervals.
The latter holds only if the screen is blanked or hidden during the occlusion intervals.
4.2 Vision and occlusion intervals
The vision interval shall be 1,5 s and the occlusion interval shall be 1,5 s. These intervals are consistent
with the occlusion literature (see References [4], [9] to [13]).
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Periods of vision and occlusion shall automatically occur without interruption until the task is
completed or the trial is terminated (see 4.4). Thus the pacing of the occlusion intervals is controlled by
the system, rather than the participant.
4.3 Task timing
The total shutter open time (TSOT) shall be defined as follows:
— Start: Timing starts with the beginning of the first vision interval;
— End: Timing ends when the instructed task has been completed and the participant says he or she
is “done”;
— Duration: Tasks are timed from start to end without interruption, including errors and subtracting
occlusion intervals. Individual system response delays greater than 1,5 s are accounted for by the
procedure in Annex A. If the task is completed during a vision interval, then only that part of the
vision interval that was used for the task should be included in the TSOT.
As an alternative, TSOT may be approximated by the number of vision intervals needed to complete
the task multiplied by the 1,5 second vision interval. Another approximation is provided by
(TTT /3,0) × 1,5. Individual system response delays greater than 1,5 s are accounted for by the
Occl
procedure in Annex A.
Figure 2 — Measurement of total task time in occluded conditions
The total task time unoccluded (TTT ) shall be determined as follows:
Unoccl
— Start: timing starts at the end of the task instruction;
— End: timing ends when the instructed task has been completed and the participant says he or she
is “done”;
— Duration: tasks are timed from start to end without interruption, including errors. Individual
system response delays that are greater than 1,5 s are accounted for by the procedure in Annex A.
The total task time in occluded conditions (TTT ) shall be determined as follows (see Figure 2):
Occl
— Start: timing starts with the beginning of the first vision interval;
— End: timing ends when the instructed task has been completed and the participant says he or she
is “done”;
— Duration: tasks are timed from start to end without interruption, including errors. Individual
system response delays that are greater than 1,5 s are accounted for by the procedure in Annex A.
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4.4 Exclusion of trials
There may be occasions when a participant refuses to complete a trial, when a participant says he or
she is done with a trial but they are not, when the experimenter judges that the participant cannot
successfully complete a trial in spite of multiple efforts, and/or when there is a trial where the TTT
Occl
[15]
is more than four times the average TTT for all the trials completed by that participant . In such
Unoccl
instances, the result should be documented and that trial should be then excluded from the analysis.
The participant should make a reasonable number of attempts to successfully complete five trials. If the
majority of participants fail to complete five trials, then the interface design should be reviewed. The
experimenter may restate the task if necessary.
5 Assessing visual demand
5.1 Selection of tasks
This document applies to any means of visual occlusion, but this method is not appropriate for tasks
with duration less than approximately 5 s TTT .
Unoccl
NOTE The occlusion procedure described in this document does not apply to tasks shorter than 5 s,
because there are not enough shutter open and closed periods. In this case, the resolution of the methodology is
inadequate.
EXAMPLE 1 Pressing a button to turn the audio system on or off.
EXAMPLE 2 Glancing at collision warning system/warning icon.
Once the task to be evaluated has been identified, the user should develop a number of examples of
that task that are broadly the same, but ideally not identical. For example, for the task “Route guidance
destination entry by postcode”, there shall be a number of possibilities, e.g. RG40 3GA and GU21 6AG.
Some of these are used for practice trials and the others for the test trials.
5.2 Participants
Consistent with conventional human factors practice, at least 10 participants should be involved
in the evaluation of each human machine interface (HMI) configuration. Ten participants is a small
enough sample that the evaluation procedure can be applied with reasonable effort, time and expense;
yet, it is large enough to provide a meaningful statistical assessment when there are five trials per
[15]
participant .
The participants shall be licensed drivers for the class of vehicle being studied (e.g. automobile, truck,
etc.) whose knowledge and familiarity with the specific driver interface under investigation is typical
of the general driving population. Persons who have specific technical knowledge or familiarity with
the system being studied shall not be included as test participants. Other relevant characteristics
of the participants should be recorded (e.g. gender, age and driving experience). At least 20 % of the
participants should be over 50 years of age.
5.3 Training
Before the first training session, each participant should be familiarized with the occlusion procedure
using a similar visual-manual task. Prior to conducting the test trials, as per 5.4, for each task, the
participant should be given a clear explanation of the system operation and the task of interest. Each
participant should have at least two and up to five practice trials for each task being investigated. Fewer
than five practice trials can be used if the participant is judged to be adequately prepared for the task.
Participants shall be told that they may operate the controls during an occluded period. The participant
should be required to successfully complete a task without intervention from the experimenter and to
verbally acknowledge that he or she is “comfortable with the task”. Note that the participant should be
trained on a given task just before administering the test trials for that task. The participant should not
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ISO 16673:2017(E)
be trained on all tasks prior to the test trial for a given task. The number of practice trials should be
recorded for each participant and task.
At least two of these practice trials should use the occlusion procedure.
Any data to be viewed or entered for the specific tasks in practice trials should be different from that in
test trials but equivalent in difficulty. The aim should be for each practice task to be properly completed
using the designated method; the experimenter should aim to ensure the appropriate completion of
the task by providing coaching or assistance if the participant is having problems with the task. If
participants cannot successfully complete the practice task at least once in five trials, then the interface
design and training protocol should be reviewed.
The participant shall be instructed to say “done” at the moment he or she believes that the task is
completed.
5.4 Test trials
After training, each participant should be tested individually. As each trial is completed, the participant
should be given the next trial. Coaching should not be provided during test trials but feedback on errors
is permitted when a trial is completed. “Successful” or “not successful” completion of the task shall be
recorded for each trial.
For each task, each participant shall be asked to complete five trials. The specific data to be viewed or
entered for each of the five test trials should be unique but representative of the level of difficulty for
that task. If there are two or fewer successful trials out of five for two or more participants, the task or
interface design should be reviewed.
5.5 Experimental plan
The experimental plan will depend on whether the user is calculating only the TSOT metric, or both
TSOT and R metrics. These metrics are described in 5.6.
To calculate only TSOT, there is no need to conduct unoccluded (static) test trials. The test plan is shown
in Figure 3 a).
Measurement of R requires a comparison of occluded and unoccluded (static) measurements. An
experimental plan to accomplish such a comparison should be designed to avoid carry-over or training
effects between the conditions [see Figure 3 b)]. The plan should also ensure that instructions to
participants are identical and that tasks are of equivalent difficulty (see Reference [7] for an example).
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ISO 16673:2017(E)
a) When calculating TSOT only, static (unoccluded) condition is not needed
b) When calculating R, balancing occluded and unoccluded (static)
conditions using two groups of participants
Figure 3 — Test plan for each task
5.6 Calculation of visual demand metrics
5.6.1 General
Testing with visual occlusion encourages the design of the driver-vehicle interface dialogues that can
be completed in a few, brief glances by identifying those dialogues that require more sustained visual
attention. The methods for calculating TSOT and R are described in this document.
5.6.2 Calculating TSOT
The TSOT value shall be recorded for each trial for a given task as described in 4.3.
If one of the TSOT values is an outlier, it should be removed from the data.
NOTE An outlier is an observation that lies outside the overall pattern of a distribution. Usually the prese
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