ISO/TR 21974-1:2018

TECHNICAL ISO/TR
REPORT 21974-1
First edition
2018-11
Naturalistic driving studies —
Vocabulary —
Part 1:
Safety critical events
Études naturalistiques de conduite — Vocabulaire —
Partie 1: Événements critiques de sécurité
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
Annex A (informative) Conceptual Framework for Categorizing Safety-critical events (SCEs)
in Naturalistic Driving Data . 5
Annex B (informative) Principles of Conflict Classification .11
Annex C (informative) Additional Conflict Attributes.28
Bibliography .52
Foreword
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This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 39,
Ergonomics.
A list of all parts in the ISO 21974 series can be found on the ISO website.
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iv © ISO 2018 – All rights reserved

Introduction
A better understanding of driver behaviour is critical to future improvements in transportation safety.
Naturalistic Driving Studies (NDSs), which observe driver behaviour in a “natural” or uncontrolled
driving environment, offer unique insight into drivers’ typical behaviour under both “normal” driving
conditions and during the critical seconds before a crash or other safety-critical event (SCE). Much
of the value and power of NDSs lies in the video that is recorded of the driver and the environment
surrounding the vehicle. Although rich in information, video should be manually reviewed and coded
by trained data coders before it is scientifically analyzed. Given the potential for human error and
interpretation, coding protocols that are well-designed, thoroughly tested, and standardized across
studies are essential.
Naturalistic driving data sets, such as the Second Strategic Highway Research Program (SHRP 2), are
becoming more available to a diverse group of researchers. As a result, it is important to have a common
terminology for monitoring, coding, and analyzing data to allow research protocols to be replicated and
results to be compared across studies. In fact, the research community has called for the development of
fully tested, common coding protocols for use in NDSs. This document addresses that need by providing
a standard vocabulary for coding SCE characteristics in NDSs. The foundation for this document came
from the SHRP 2 naturalistic driving study annotation effort and subsequent revisions to the SHRP 2
[1]
dictionary to accommodate heavy vehicles (trucks and buses) . Substantial improvements have been
made to this document in both content and structure. However, large parts of this document are largely
verbatim with the original foundational documents.
It is recommended that vehicles in these studies be instrumented with at least a forward-looking view
and an in-vehicle view capturing the driver’s face and upper body. Rear- and side-facing views are
often helpful when interpreting conflicts that occur behind or next to the instrumented vehicle. A view
capturing the steering wheel, driver’s hands and/or dashboard can be helpful for additional analyses
(which are outside the scope of this document). However, equipment and labor costs may make these
additional views unfeasible. In addition, basic measurements of the kinematics of the instrumented
vehicle should be available, including at least longitudinal acceleration, lateral acceleration, and vehicle
speed. Other kinematic measurements that help assess conflict situations (if feasible) include brake and
throttle pedal application and/or pressure, proximity to and speed of surrounding non-instrumented
vehicles (e.g., via radar), latitude and longitude, and activation of key vehicle safety systems (e.g., anti-
lock brakes).
The main objective of this document is to define different types of SCEs based on a taxonomy of general
conflict classes and a set of basic variables for characterizing the events. The definitions supplied here
apply to data collected from light and heavy vehicles [i.e., category M and N according to Classification
and definition of power-driven vehicles and trailers: Council Directive 70/156/EEC (as amended by 92/53/
EEC), Annex 2]. However, this does not preclude the definitions specified in this document from, with
caution, being adapted for use with data collected from other vehicle types such as powered two-
wheelers or an infrastructure-based (rather than vehicle-based) data collection system.
This document does not address methods for identifying candidate SCEs (also referred to as triggers),
a complete set of annotations for these SCEs (e.g., driver distraction), or the recommended approach to
analyzing this data. This document also does not address the definition, extraction, or annotation of
controls. These controls, often called baselines in transportation literature, are selected for comparison
to events of interest in epidemiological as well as other analyses. Since the definition, extraction, and
annotation of these controls are highly dependent on the research question of interest, they have been
excluded from the scope of this document. The scope of the present document is graphically illustrated
in Figure 1.
Figure 1 — Document scope
vi © ISO 2018 – All rights reserved

TECHNICAL REPORT ISO/TR 21974-1:2018(E)
Naturalistic driving studies — Vocabulary —
Part 1:
Safety critical events
1 Scope
This document defines terms and definitions commonly used for the annotation of video from NDSs
collected during real-world driving in an uncontrolled setting.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminological databases for use in standardization at the following URL
addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
combined avoidance capacity
total response capacity of all responding conflict partners (3.3)
Note 1 to entry: The capacity of a responding conflict partner takes into account both the abilities and limitations
of the vehicle or road user as well as any environmental or infrastructural constraints, if present.
Note 2 to entry: Conflict partners that do not exhibit an observable response are not included in this construct.
3.2
conflict
situation where the trajectory(ies) of one or more road users or objects (conflict partner; 3.3) led to one
of three results: 1) a crash (3.4) or road departure (3.12), 2) a situation where an evasive manoeuvre(s)
(3.5) was required to avoid a crash or road departure, or 3) an unsafe proximity between the conflict
partners
Note 1 to entry: The key concept underlying the present framework is that of conflict.
Note 2 to entry: Three general classes of traffic conflict are of interest in naturalistic driving analyses: trajectory
conflict (3.2.1), single-vehicle conflict (3.2.2), and proximity conflict (3.2.3).
3.2.1
trajectory conflict
crash course between at least two conflict partners (3.3)
3.2.2
single-vehicle conflict
conflict (3.2) involving loss of vehicle control (e.g., horizontal and/or lateral skidding or rotation) or
proximity to the road edges (e.g., road departure; 3.12) rather than proximity to another entity
3.2.3
proximity conflict
conflict (3.2) involving two or more entities that are not on a crash course but nevertheless come in
close temporal and/or spatial proximity to a crash (3.4)
3.3
conflict partner
any entity that is part of a conflict (3.2)
Note 1 to entry: This may include other vehicles (3.18), pedestrians (3.10), pedal cyclists (3.9), other non-motorists
(3.8), other road users, animals, and objects (including roadside barriers that exceed the ground clearance of the
affected vehicle).
Note 2 to entry: If a conflict partner (3.3) is present, then the conflict is either a trajectory conflict (3.2.1) or a
proximity conflict (3.2.3).
Note 3 to entry: Low roadside barriers (e.g., curbs) within the ground clearance of the vehicle are not considered
conflict partners.
3.4
crash
situation in which the subject vehicle (i.e., instrumented vehicle; 3.14) has any contact with at least one
other conflict partner (3.3) either on or off the trafficway (3.15), either moving or stationary (fixed or
non-fixed), that is observable or in which kinetic energy is measurably transferred or dissipated
Note 1 to entry: This excludes roadway (3.11) features meant to be driven over such as speed bumps and low
roadside barriers (curbs, medians, etc.) within the ground clearance limitations of the vehicle.
Note 2 to entry: A crash may also be a single-vehicle conflict (3.2.2) that includes at least one of the following
conditions: vehicle rollover, airbag deployment, injury, more than 90° degrees of horizontal vehicle rotation, or
all four tires leaving the trafficway.
3.5
evasive manoeuvre
any action performed by any conflict partner (3.3) to change its trajectory or speed in an attempt to
avoid or reduce the severity of a potential crash (3.4), avoid or reduce the severity of a road departure
(3.12), or regain vehicular control after a loss of control
Note 1 to entry: Examples include steering, braking, accelerating, running, stopping, or a combination of these.
Note 2 to entry: At least one of the manoeuvres exceeds normal vehicle control inputs.
3.6
metadata
information that provides a description about the structural content of its referenced dataset or the
methods with which the data were collected
Note 1 to entry: Examples of metadata include location (e.g., country, region) of data collection, sampling
methods, units of measure, etc.
3.7
naturalistic driving study
NDS
any driving study where research subjects are recruited to drive on public roads (not in a simulator or
on a test track), where there is no in-vehicle experimenter or confederate vehicles, and where dr
...