Above and beyond driving abilities: toward a single index

Abstract

The present study allows us to pave the way toward a single and common indicator of driving behavior. We investigated performance in several tests known to assess key process of driving fitness such as driving maneuvering, visual and visuocognitive abilities. We propose a methodology to bring together all these measures under a single index we call the Driver’s Safety Index. The results indicate that this index might be helpful to characterize driving behaviors and to pin down the kind of limitations an individual must deal with to effectively control a vehicle. The present investigation is the first step toward an intended index, which might be translated in licensing policies. It also calls for further clinical investigations to refine the visual criteria necessary in its computation. Importantly, we evidence that visuo-cognitive performance, a parameter overlooked up to now, is crucial to consider for assessing driving abilities and should be incorporated in such an index.

Full text

1Points de Vue – International Review of Ophthalmic Optics
online publication - January 2018
The present study allows us to pave the way toward a single and common
indicator of driving behavior. We investigated performance in several tests known to
assess key process of driving fitness such as driving maneuvering, visual and visuo-
cognitive abilities. We propose a methodology to bring together all these measures
under a single index we call the Driver’s Safety Index. The results indicate that this
index might be helpful to characterize driving behaviors and to pin down the kind
of limitations an individual must deal with to effectively control a vehicle. The present
investigation is the first step toward an intended index, which might be translated in
licensing policies. It also calls for further clinical investigations to refine the visual
criteria necessary in its computation. Importantly, we evidence that visuo-cognitive
performance, a parameter overlooked up to now, is crucial to consider for assessing
driving abilities and should be incorporated in such an index.
ABOVE AND BEYOND
DRIVING ABILITIES:
TOWARD A SINGLE INDEX
SCIENCE
KEYWORDS
driving, vision, visuo-cognitive abilities, index, safety
Prof. Jocelyn Faubert
Dr. Romain Chaumillon
NSERC/Essilor Industrial Research Chair in
Visual Function of Montréal University, School
of Optometry, Quebec, Canada.
Visual Psychophysics and Perception
Laboratory, School of Optometry, Montréal,
Quebec, Canada
Prof. Delphine Bernardin
Jesse Michaels
NSERC/Essilor Industrial Research Chair in
Visual Function of Montréal University, School
of Optometry, Quebec, Canada.
Visual Psychophysics and Perception
Laboratory, School of Optometry, Montréal,
Quebec, Canada
NSERC/Essilor Industrial Research Chair in
Visual Function of Montréal University, School
of Optometry, Quebec, Canada.
Visual Psychophysics and Perception
Laboratory, School of Optometry, Montréal,
Quebec, Canada
Essilor Canada Ltd., Montréal, Quebec, Canada
NSERC/Essilor Industrial Research Chair in
Visual Function of Montréal University, School
of Optometry, Quebec, Canada.
Visual Psychophysics and Perception
Laboratory, School of Optometry, Montréal,
Quebec, Canada
Based on the understanding of the vision of human
in mobility, and how it perceives, makes decision and
interacts with our world in movement, the NSERC-
Essilor VisAge Chair has an impressive story from
2001 until now, fostering innovation in the field of
optics and vision health. Here, we focus on one of its
recent exploration and understanding: how to define
driving behavior.
The industrialized world is continuing to see a marked
demographic transformation, with the proportion of
individuals over the age of 65 growing ever higher.
This demographic shift and its inevitable social,
medical and economic consequences has been and
will continue to represent a tremendously important
topic of investigation for driving safety. Indeed, when
accounting for the relative amounts of kilometers
they drive, elderly drivers are known to be involved in
more fatal crashes (Insurance Institute for Highway
Safety, 2014)1 and have more traffic convictions
when compared to any other adult age group.
Considering that driving is the principal mode of
travel for adults worldwide it is crucial to understand
what factors are involved in the observed age-related
decline in driving fitness to translate these factors in
licensing policies.
In the few countries assessing more than simple
vehicle maneuvering abilities, the second criteria
considered to obtain or renew a driving license is
visual acuity. This is undoubtedly consistent since it

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is well-accepted that good eyesight is preponderant to
drive safely (see for a review Owsley & McGwin,
2010).2 Indeed, vision is a crucial sense to make
decisions on the road, and poor vision can notably
decrease chances of reacting in time, putting oneself and
others at greater risk. Nevertheless, eyesight is only the
first step in perception mechanisms and how we use
this visual information, whether or not it is altered by
age-related ocular diseases, is also a key parameter in
the decision-making process when facing or
anticipating an impending hazard. This is especially
true in a daily task such as driving which, despite its
apparent ease, is known to be a complex task involving
multiple visuo-cognitive processes such as visuo-
spatial skills, processing speed as well as attentional
processes. Accordingly, we think that simple measures
of vehicle manoeuvring and visual acuity alone cannot
be sufficient to faithfully capture the whole and
complex picture of driving fitness.
In the context of the VisAge chair, we seek to better
define the different drivers’ profiles to be able to offer
them individualized solutions. Therefore, the present
study aimed at better characterizing drivers’ profiles
through i) a further exploration of these visuo-cognitive
abilities and ii) linking them with the other determining
factors such as visual abilities and vehicle maneuvering
measures.
Methodology
A total of 115 licensed drivers between the ages of 18
and 86 were recruited for the study. To assess the
efficiency of our characterization among a wide age-
range, the participants were separated into two groups:
64 young participants (mean age= 28.8 ± 10.23 (SD)
years old) and 51 older participants (mean age= 77.2
± 5.01 (SD) years old). Each participant was involved
in three different experimental phases:
1) Visual tests including a visual acuity test (Snellen
chart), a stereoscopic vision test (Randot test) and a
binocular Esterman visual field test run on the Humphrey
Visual Field Analyzer. Those tests gave rise to an accurate
score representing a visual ability subclass: V1-Acuity,
V2-Stereo and V3-Visual Field, respectively.
2) Driving tests were performed using a high-fidelity,
moving base driving simulator (Figure 1). Three scenarios
were designed to represent natural driving environments
with an increasing visual attentional load: highway (i.e.
low), rural (i.e. middle) and city (i.e. high). Based on a
recent method developed at the NSERC-Essilor Chair, the
rural scenario appeared as the most efficient for detecting
subtle differences in driving maneuver ability (Michaels et
al. 2017).3 We also identified some variables merging as
significant and non-redundant measures of driving
behavior (see Table 1). Since we aimed at characterizing
drivers’ behaviour, the driving measures presented
hereinafter will be those recorded during the rural scenario.
3) A visuo-cognitive task known as 3-Dimensional Multiple
Object Tracking (3D-MOT; Figure 2) to assess the
individual’s ability to capture and integrate relevant
information in a highly complex visual environment
(Pylyshyn & Storm, 1988; Faubert & Sidebottom, 2012).4,5
The individual’s score (hereinafter called “visuo-cog”)
corresponds to the mean speed threshold at which he was
able to simultaneously track 4 among 8 balls. To further
explore the relevance of the visuo-cognitive measure, we
investigated the link between this measure and the usual
driving and visual measures mentioned above.
Main findings
As illustrated in Figure 3 panel left, the results evidenced
strong correlations between the visuo-cognitive score and
several driving measures as well as with some visual
measures. Visuo-cognitive score is correlated with driving
measures known to be main indicators of diminished
Table 1: Description of the nine driving measures involved

3Points de Vue – International Review of Ophthalmic Optics
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SCIENCE
Integrative approach toward a single Driver’s Safety
Index
We established a methodology to link these three
categories of driving behavior assessment by building a
unique indicator. Determining a unique indicator of
safe driving behavior represents both a need and a risk.
This is needed to build screening tests, which could
then be readily translated into licensing policies.
Nevertheless, this is also a risk because resuming
driving behavior into one unique score might lead to
neglect or underestimation of important components of
driving abilities. Instead of looking for the best predictor
of driving behaviour, we proposed a global score in
which each important driving component makes its
contribution. Attempting to do so, we computed the
area of the three different parts of a radar chart
visualization and built a global index. The first area
included the indicators from D1 to D9 and corresponds
to an index of driving maneuver abilities (“Idri”). The
second area involved the V1-Acuity, V2-Stereo and
driving abilities such as the number of crashes (r= -.31;
p< .001), the mean speed naturally adopted (r= .47;
p< .001) and the standard deviation of lane position
(r= -.26; p= .005). Furthermore, this score is also
correlated with the stereoscopic vision capacity (r= -.44;
p= .001) and to a lesser extent with visual acuity
(r= -.25; p= .07). Because one of the advantages of
this visuo-cognitive task is the involvement of a three-
dimensional virtual environment, the link between
visuo-cognitive score and stereoscopic vision we
observed was expected.
Additionally, the multiple linear regression analyses
presented below reveal that the visuo-cognitive score is
a better predictor of car driving and visual abilities as
compared to chronological age and naturally adopted
mean driving speed. Taken together, these results
reinforce the idea that visuo-cognitive abilities are key
processes in car driving. As a relevant predictor of driving
performances across age, this visuo-cognitive score
should be included in the battery of visual tests for
identifying drivers with hampered driving abilities.
« Taken together, these results reinforce the
idea that visuo-cognitive abilities are key
processes in car driving. »
Figure 2: illustration of the visuo-cognitive task. Firstly, 8 randomly positioned spheres
are presented in a virtual volumetric space. Secondly, the 4 spheres to be tracked during
the trial are quickly highlighted in color. Thridly, all spheres turn back to their original color
and begin to move. Finally, the observer is asked to respond by indentifying the spheres he
had to track. Then, feedback is given to the observer. If the observer correctly identifies all
spheres, the task is repeated at a faster speed. If, on the other hand, the observer makes
a mistake, the task is repeted at a slower speed.
Figure 1: Picture of the VS500M driving simulator.3

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V3-Visual Field indicators and corresponds to an index
of visual abilities (“Ivis”). The third area represents an
index of visuo-cognitive abilities (“IvisCog”). Finally, the
sum of these three areas gives rise to a global index, we
called Driver’s Safety Index (DSI), thought to represent
the amount of limitations an individual must deal with
to effectively control a vehicle.
Application of the Driver’s Safety Index to a comparison
between two individuals
The use of our DSI associated with a radar chart
visualization show, in one straightforward and clear
picture, which components of driving might be less
developed in one individual and simplifies the
comparisons between two individuals (Figure 4) or two
groups (Figure 5).
As an example, when comparing the results obtained by
the individuals showing the lowest and the highest
visuo-cognitive scores in older (Figure 4a) as well as in
younger group (Figure 4b), the radar chart visualizations
and DSI appear to be informative and help to avoid
misinterpretation. Indeed, if we only consider visual
abilities, the conclusion we would draw would be that
the two drivers have the same driving abilities.
Nevertheless, considering DSI indicates that in both
groups, individuals who obtained the best visuo-
cognitive scores have more preserved driving skills than
the drivers who obtained the lowest visuo-cognitive
performance. This wide difference is revealed by a DSI
in the highest performers being twice as high as the DSI
of the lowest performers.
Application of the Driver’s Safety Index to a comparison
between two groups
When considering the lowest and highest performance
among a population, differences are obviously wide.
Nevertheless, when attempting to compare the mean
performance obtained in two groups, differences might
be more subtle and less straightforward to analyze. The
picture below illustrates performances recorded for the
oldest half and for the youngest half of individuals in
the Older group (Figure 5a), and those recorded for the
lowest half versus highest half in visuo-cognitive
performance among the Older group (Figure 5b). In
such a situation, the DSI appears to be a relevant tool
to compare the two groups since it allows one to
decipher that driving performance was not dependent
on chronological age (DSI: Oldest= 61.25;
Youngest= 61.95; p= .89) but, rather, that participants
were classified depending on their visuo-cognitive
performances (DSI: Lowest_VCI= 51.82;
Highest_VCI= 70.98; p< .001).
Discussion
Visual and visuo-cognitive assessment for driving should
be considered as important as other road safety campaigns
by authorities. Despite this fact, strict regulations to
obtain or renew a driving license are still weak in most
countries. One of the reasons explaining this absence of
standards is the lack of homogeneous, simple and
reliable criteria. Moreover, when a visual criteria is
included in the requirements, like in North America and
Australia, the tests are usually restricted to visual acuity
and visual field assessments. Importantly, previous
works already showed that visual acuity, when
considered as an independent contributor to renewal
Figure 3: Bi-variate correlations and multiple linear regression analysis showing the relevance of the visuo-cognitive measure.

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SCIENCE
Future investigations and improvements of the Driving
Safety Index will bring new, more comprehensive
knowledge of and a powerful method to characterize
driving abilities. Here, we considered visual acuity,
stereoscopic ability and the functional visual field of our
participants, but many others criteria could be incorporated
in its computation. Further studies like the ones from
Wood & Owsley (2016)8, are needed to clarify which visual
tests, such as for instance the contrast sensitivity test, are
the most relevant to understand what visual deficits can
hamper driving. Moreover, our observations on the driving
simulator must be replicated in actual on-road driving.
Finally, it is worth noting that we only included individuals
with optimal or corrected-to optimal vision. It will therefore
also be of interest to assess the functionality of this
indicator with a population suffering from visual deficits
decision, had no impact on fatality rates in adults aged 65
years old (Grabowski et al. 2004)6 and no economic
benefit for society (Viamonte et al. 2006).7
The two important results of this study help to highlight
the relevance of the establishment or improvement of
such criteria. Firstly, our results suggest that visuo-
cognitive performance, as a central component of vehicle
driving, can provide additional information on the
participants’ driving efficiency and the limitations they
face. As such, it should be considered in the battery of
tests leading to obtain or renew a driving license. Secondly,
the computation of the Driving Safety Index might be
helpful to easily characterize driving behavior with the
advantage being that it merges a large panel of abilities
that are recognized as central for safe driving.
Figure 4: The radar chart representation and the global Driver’s Safety Index (DSI). The individuals with highest (in blue) ansd lowest (in pink) visuo-cognitive
index (VCI) among a) older and b) younger participants are represented. To balance / normalize the different indicators, all scores are expressed as a percentage
of the best performance observed accross the 115 participants and are thus reported on the same scale.
Figure 5: Characterization of two populations through Driver’s Safety Index. a) Classification depending on the chronological age: comparison between the
Oldest 50% (in pink) and the Youngest 50% (in blue) among individuals in the Older group. b) Classification depending on the visuo-cognitive indicator (VCI):
comparison between the Lowest 50%(in pink) and the Highest 50% (in blue) visuo-cognitive scoresamong the older group. Dashed lines respresent SEM.

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• Assessing driving ability is a very difficult task
and there has been no clear indicator
until now.
• Two main needs are identified: to further explore
an overlooked dynamic aspect of driving fitness
(visuo-cognitive abilities) and to determine a unique
indicator which could be readily translated into
licensing policies.
• The results demonstrated that visuo-cognitive
abilities should be considered by licensing
authorities for identifying drivers with hampered
driving abilities.
• We propose a global score, called Driver’s Safety
Index (DSI), in which each important driving
component considered in the present study makes its
contribution.
• The DSI is helpful in easily characterizing driving
behavior with the advantage of merging a large
panel of abilities that are recognized as central for a
safe driving.
• The DSI is relevant to determine which components
of driving are less developed in one individual and
simplifies the comparisons between different
individuals / groups.
• Our demonstration calls for further studies to
clarify which visual tests would be the most relevant
to unravel visual deficits that can hamper driving.
• The above takeaway suggests an increasing
interest to involve eye care professionals
in the improvement of this DSI.
• Behind the accuracy of this score there is a major
public health issue: to guarantee the optimum
driving safety of road users while preserving the
autonomy of the elderly.
KEY TAKEAWAYS
Conclusion
We demonstrated that driving abilities, evaluated within a
driving simulator, are strongly associated with the 3D-MOT
scores. This result highlights the importance to consider the
visuo-cognitive abilities in the assessment of driving abilities.
Moreover, this study paves the way toward a single,
common indicator of driving behaviour. However, its
approval will require the involvement of eye care
professionals and other health clinicians to further refine
which visual criteria might be relevant to include in its
computation. Refining these criteria will allow to frame
them by standards data for each population or even
targeting specific complains such as depth perception,
glare or driving at night, and thus make the Driver’s Safety
Index more reliable and powerful. There is a two-fold
challenge behind designing a measure upon which one
can base decisions concerning license renewal:
guaranteeing the optimum driving safety of road users
while also preserving the autonomy of the elderly for as
long as possible to avoid the potential adverse
consequences of driving cessation.
SCIENCE
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