Accident Analysis and Prevention 81 (2015) 120–123

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Accident Analysis and Prevention
journal homepage: www.elsevier.com/locate/aap

Older drivers’ risks of at-fault motor vehicle collisions
Masao Ichikawa a, * , Shinji Nakahara b , Ayako Taniguchi caFaculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
Kanagawa University of Human Services, 1-10-1 Heisei-cho, Yokosuka, Kanagawa 238-8522, Japanc
Faculty of Engineering, Information and Systems, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japanb

A R T I C L E I N F O

A B S T R A C T

Article history:
Received 2 December 2014
Received in revised form 13 March 2015
Accepted 5 May 2015
Available online 14 May 2015

In aging societies, increasing numbers of older drivers are involved in motor vehicle collisions (MVCs),
and preserving their safety is a growing concern. In this study, we focused on whether older drivers weremore likely to cause MVCs and injuries than drivers in other age groups. To do so we compared at-fault
MVC incidence and resulting injury risks by drivers’ ages, using data from Japan, a country with a rapidly
aging population. The at-fault MVC incidence was calculated based on distance traveled made for noncommercial purposes, and the injury risks posed to at-fault drivers and other road users per at-fault
MVCs. We used MVC data for 2010 from the National Police Agency of Japan and driving exposure datafrom the Nationwide Person Trip Survey conducted by a Japanese governmental ministry in 2010. The atfault MVC incidence showed a U-shaped curve across the drivers’ ages, where teenage and the oldest
drivers appeared to be the highest risk groups in terms of causing MVCs, and the incidence was higher for
female drivers after age 25. The injury risk older drivers posed to other vehicle occupants because of theirat-fault MVCs was lower than for drivers in other age groups, while their own injury risk appeared muchhigher. As the number of older drivers is increasing, efforts to reduce their at-fault MVCs appear justiﬁed.
ã 2015 Elsevier Ltd. All rights reserved.

Keywords:
Older drivers
At-fault collision risk
Drivers’ relative risk

1. Introduction
Ensuring the safety of older drivers presents a growing concern
because the number of such drivers and their involvement inmotor vehicle collisions (MVCs) is increasing (Organisation for
Economic Co-Operation and Development, 2001; Kohata andOroku, 2011). This concern is reﬂected in licensing policies applied
to older drivers. Many countries now set stringent policies such as
shortening the license renewal interval and requiring medical
examinations (Kahvedžic, 2013). In Japan, drivers aged 70 or older
at the time of renewal are obligated to take a driving lesson
consisting of a lecture, driver aptitude test (testing for sensory
motor skills using a driving simulator, as well as for ﬁeld of vision,
kinetic and night vision), an on-road driving assessment, and a
discussion session. Drivers 75 or older must also take a paperbased cognitive screening test before the lesson to assess whether
they have adequate cognitive function for driving. Older drivers arealso encouraged to surrender their licenses (Doi, 2014).

* Corresponding author. Tel.: +81 29 853 3423; fax: +81 29 853 3423.
E-mail addresses: masao@md.tsukuba.ac.jp (M. Ichikawa),
nakahara-sry@kuhs.ac.jp (S. Nakahara), taniguchi@risk.tsukuba.ac.jp (A. Taniguchi).
http://dx.doi.org/10.1016/j.aap.2015.05.004
0001-4575/ ã 2015 Elsevier Ltd. All rights reserved.

Notwithstanding the increased number of MVCs caused byolder drivers, it is beneﬁcial to examine such drivers’ relative safety
in terms of an “at-fault” rate that clariﬁes the probability of causing
MVCs per unit of risk exposure. This risk exposure should bequantiﬁed in ways such as distance traveled and number ofvehicular trips, rather than the number of licensed drivers. This isbecause license holders are not necessarily current drivers anddriving patterns typically vary by driver age. Two previous studies
took these aspects of risk assessment into account. Williams andShabanova (2003) reported that fatalities in MVCs caused by young
licensed drivers were the highest of all age groups, and more thanhalf were of passengers and of occupants of other vehicles. In
contrast, the large majority of fatalities in MVCs caused by older
drivers were of the drivers themselves. Tefft (2008) further
considered the amount of MVC risk exposure as mentioned above,and presented a U-shaped curve of the mortality rate across age
groups. The rate was high among young and older drivers, but
young drivers posed the highest fatal risk to their passengers,
occupants of other vehicles, and non-motorists; while older
drivers’ greatest risk was to themselves.
While these previous studies examined mortality rates, thelikelihood of causing MVCs, irrespective of fatalities, is a safetyconcern for older drivers, even if they were overrepresented in
MVCs because of their susceptibility to injury (Li et al., 2003;
Meuleners et al., 2006). Another concern for older drivers is theM. Ichikawa et al. / Accident Analysis and Prevention 81 (2015) 120–123

morbidity of injuries in their at-fault MVCs not only for the drivers
themselves but also for other road users involved in the MVCs. In
the present study, we therefore examined the incidence of at-fault
MVCs including both fatal and non-fatal collisions and themorbidity of injuries for the persons involved in the MVCs. We
focused on MVCs that occurred while driving for non-commercial
purposes, under the assumption that older drivers less frequently
engage in commercial driving. We used the at-fault drivers’ ages asa means to examine the relative safety of older drivers comparedwith other age groups by comparing the incidence of at-fault MVCs
and the morbidity of injuries.
2. Methods
2.1. Data
Japan’s Institute for Trafﬁc Accident Research and Data Analysis
compiles data on all MVCs reported to the National Police Agencyof Japan. The data are collected in a standardized format
throughout Japan that includes the purpose of driving and driver’s
responsibility for the MVC. Responsibility is determined by thepolice investigators at the scene of the MVC. We adopt the term
“at-fault driver” to indicate the driver primarily responsible for an
MVC. We obtained the above-mentioned institute’s data on thenumber of MVCs (resulting in at least one fatal or non-fatal injury
to any road users) that at-fault drivers caused while driving a midsized or smaller motor vehicle (car, van or truck) for noncommercial purposes, separated into the age of the at-fault driver,including drivers in single-vehicle collisions. Numbers of fatal andnon-fatal injuries in those MVCs were also obtained and combined
for analysis. In the police data, fatal injuries or deaths are deﬁned as
deaths occurring within 24 h of the collision. As mentioned above,
we targeted MVCs in non-commercial purposes. Our focus was therelative safety of non-commercial drivers by age.
Vehicle kilometers traveled (VKT) made by driving for noncommercial purposes were estimated in each age stratum using
the data of the Nationwide Person Trip Survey conducted in

1212010 by the Japanese Ministry of Land, Infrastructure, Transport
and Tourism, as well as the Japanese population census
conducted for the same year, to weight the data. The survey
involved approximately 38,000 households in 70 cities and
60 towns and villages. To clarify average trip patterns, survey
respondents recorded travel information such as the purpose,mode, time, distance and destination of each trip on a given
weekday (Tuesday, Wednesday or Thursday) or on Sunday in
October or November 2010. The survey was not designed toestimate driving exposures throughout the year; i.e., possible
variations in exposures by month and day cannot be adjustedwith the survey data to extrapolate total driving exposures in2010. The number of licensed drivers by age in 2010 was obtained
from Driver’s License Statistics (National Police Agency, 2010).
The data are shown in Table 1.
2.2. Analysis
In line with the exposure measurement, we analyzed the data of
MVCs that occurred on the aforementioned days in October andNovember 2010. The number of at-fault MVCs and their resultant
fatal and non-fatal injuries were stratiﬁed by the sex and age groupof the at-fault drivers. The at-fault MVC incidence of drivers of agiven age group was expressed as the number of at-fault MVCs per
million VKT. This measure was calculated separately for MVCs withany type of motor vehicles (excluding motorcycles) or singlevehicle collisions, and for MVCs with motorcycles, bicycles orpedestrians. Single-vehicle collisions were combined with collisions with any type of motor vehicles because they share only 4.5%of the total of those.
The morbidity of injuries for the persons involved in the MVCs
caused by drivers of a given age group was expressed as thenumber of fatal and non-fatal injuries per 100 at-fault MVCs. Thismeasure was calculated separately for at-fault drivers; for at-fault
drivers’ passengers; for the occupants of other vehicles struck(other vehicle occupants); and for motorcyclists, cyclists andpedestrians.

Table 1
Numbers of licensed drivers and vehicle kilometers travelled (VKT) by sex and age, and numbers of at-fault motor vehicle collisions (MVCs) and fatal or non-fatal injuries bysex and age of at-fault drivers, 2010.
Driversex

Driverage

Licenseddrivers

VKT

At-fault MVCs involving:

Injuries to:

Motor vehicle/
single collision

Motorcycles, bicycles
and pedestrians

At-fault
drivers

At-fault drivers’
passengers

Other vehicle
occupants

Motorcyclists, bicyclists
and pedestrians

Male

18–19
20–24
25–29
30–39
40–49
50–59
60–69
70–79
80–84
85–

452,028
2,720,151
3,504,129
8,875,628
8,249,240
7,625,232
7,950,356
4,193,244
805,263
246,825

29,648,455
350,750,891
958,856,900
3,435,190,583
3,654,768,820
3,607,362,877
3,587,826,314
1,105,392,109
101,711,336
17,946,823

839
2425
2046
3198
2275
1986
2201
1890
511
154

214
978
1048
2376
2074
1929
2158
1387
311
114

99
216
143
265
203
166
221
275
95
37

87
139
83
109
80
93
123
182
38
14

964
2977
2464
3874
2774
2389
2569
2112
551
152

218
989
1058
2403
2102
1953
2184
1397
314
113

Female

18–19
20–24
25–29
30–39
40–49
50–59
60–69
70–79
80–

360,7032,320,590
3,128,187
8,093,054
7,449,975
6,325,789
5,068,700
1,304,998
125,623

20,199,256
443
269,515,529 1554
516,023,350 1260
1,332,330,352 2195
1,476,490,493 1900
1,262,979,145 1527
869,622,560 1422
143,775,384
573
3,616,495
64

94
530
653
1616
1702
1336
1256
463
43

68
204
143
275
262
235
251
129
16

38
58
39
98
86
48
96
40
8

499
1793
1478
2502
2224
1746
1574
612
67

93
539
653
1624
1721
1343
1266
466
43

No. of licensed drivers is as of the end of 2010.
No. of VKT is an estimate for Tuesdays, Wednesdays, Thursdays and Sundays of October and November 2010.
No. of MVCs and injuries occurred on Tuesdays, Wednesdays, Thursdays and Sundays of October and November 2010.
For female drivers, age groups 80–84 and 85 or older were combined because of the small number of at-fault MVCs and injuries.

122

M. Ichikawa et al. / Accident Analysis and Prevention 81 (2015) 120–123

Table 2
Incidence of at-fault motor vehicle collisions (MVCs) and morbidity of fatal or non-fatal injuries by sex and age of at-fault drivers, 2010.
Driversex

Driverage

At-fault MVCs per million VKT involving:

Injuries per 100 at-fault MVCs to:

Motor vehicle/single
collision

Motorcycles, bicycles andpedestrians

At-fault
drivers

At-fault drivers’
passengers

Other vehicle
occupants

Motorcyclists, bicyclists andpedestrians

Male

18–19
20–24
25–29
30–39
40–49
50–59
60–69
70–79
80–84
85–

28.3
6.9
2.1
0.9
0.6
0.6
0.6
1.7
5.0
8.6

7.2
2.8
1.1
0.7
0.6
0.5
0.6
1.3
3.1
6.4

11.8
8.9
7.0
8.3
8.9
8.4
10.0
14.6
18.6
24.0

10.4
5.7
4.1
3.4
3.5
4.7
5.6
9.6
7.4
9.1

114.9
122.8
120.4
121.1
121.9
120.3
116.7
111.7
107.8
98.7

101.9
101.1
101.0
101.1
101.4
101.2
101.2
100.7
101.0
99.1

Female

18–19
20–24
25–29
30–39
40–49
50–59
60–69
70–79
80–

21.9
5.8
2.4
1.6
1.3
1.2
1.6
4.0
17.7

4.7
2.0
1.3
1.2
1.2
1.1
1.4
3.2
11.9

15.3
13.1
11.3
12.5
13.8
15.4
17.7
22.5
25.0

8.6
3.7
3.1
4.5
4.5
3.1
6.8
7.0
12.5

112.6
115.4
117.3
114.0
117.1
114.3
110.7
106.8
104.7

98.9
101.7
100.0
100.5
101.1
100.5
100.8
100.6
100.0

VKT: vehicle kilometers travelled.

The at-fault MVC incidence represents the risk of at-fault
collision per unit of travel, while the morbidity of injuries indicatesthe risk of injury per MVC that at-fault drivers pose to themselves
and others involved in their at-fault MVCs. These measures wereshown by the sex and age group of at-fault drivers (Table 2).
3. Results
The incidence of at-fault MVCs involving motor vehicles or
single-vehicle collisions was highest among teenage drivers. This
incidence decreased as the driver’s age advanced, but turned to anincrease around age 60–69 among females and 70–79 among
males though to a lesser extent than for teenage drivers. The
incidence of at-fault MVCs involving motorcycles, bicycles andpedestrians also showed a similar trend, but differences in theincidence between teenage and older drivers were not as large as
the incidence involving motor vehicles or single-vehicle collisions.
Moreover, the incidence for female drivers in the oldest age group
was even higher than for teenage female drivers. The incidence forfemale drivers were generally higher than for male drivers afterage 25.
In terms of the morbidity of injuries, male drivers aged 70 orolder and female drivers 60 or older were more likely to be injured
via own at-fault MVCs than drivers in other age groups. For
example, the number of driver injuries per 100 at-fault MVCs
caused by male drivers aged 85 or older was about 24 while that ofteenage male drivers was about 12. A similar trend was observed
among their passengers as older drivers tended to carry older
passengers and vice versa (data not shown).
However, the number of injuries to other vehicle occupants was
slightly lower for at-fault MVCs caused by older drivers than fordrivers in other age groups. For example, the number of injuries toother vehicle occupants per 100 at-fault MVCs caused by male
drivers aged 85 or older was about 99 while that for teenage male
drivers was about 115.
Female drivers were more susceptible to injuries than males,
while posing less injury risk to other vehicle occupants in their atfault MVCs throughout driver age groups. The number of injuries tomotorcyclists, bicyclists and pedestrians appeared almost evenacross the age groups of at-fault drivers among both sexes.

4. Discussion
Older drivers were found to be more likely to cause MVCs than
middle-aged drivers but less likely than teenage drivers even if
they were overrepresented in MVCs. Moreover, the risk of injury
older drivers posed to other vehicle occupants as a result of theirat-fault MVCs was lower than for drivers in other age groups, while
their own injury risk appeared to be much higher than for drivers
in other age groups. The incidence of collisions with motorcycles,
bicycles and pedestrians was similar between both ends of thedriver age groups with the exception of the oldest female drivers.
These ﬁndings in Japan are largely consistent with ﬁndings from
Australia (Langford et al., 2008; Meuleners et al., 2006), the United
Kingdom (Mitchell, 2013), Spain (Lardelli-Claret et al., 2011) andthe United States (Li et al., 2003; Tefft, 2008; Williams andShabanova, 2003).
To mitigate the at-fault MVC risk, a driving lesson and cognitive
test were recently added to license renewal procedures for older
drivers in Japan. However, another study found that suchinterventions were not effective in reducing at-fault MVCs amongolder drivers (Ichikawa et al., 2015). Moreover, a systematic review
on the effectiveness of retraining older drivers found no evidence
that the retraining reduces MVCs (Korner-Bitensky et al., 2009).
Therefore, instead of educating older drivers to continue driving
safely, and with the objective of reducing MVCs and injuries
especially among the oldest drivers, it might be more practical toreduce their driving by providing more convenient transportation
alternatives. This type of intervention should also be helpful for
older drivers in their preparation to stop driving in the future. A
recent national survey of Japanese adults aged 60 and above
revealed that 80% of current drivers would consider stopping
driving when they perceived their functional decline or reached acertain age, and 2% reported a desire to stop driving if public
transportation were readily available (Cabinet Ofﬁce, Governmentof Japan, 2011).
Should older drivers be assisted with continuing to drive safely,
differences among sex in the at-fault MVC incidence deserve
consideration given the increasing number of female drivers. We
found the at-fault MVC incidence of female drivers turned higher
than that of male drivers after age 25, which is similar to otherM. Ichikawa et al. / Accident Analysis and Prevention 81 (2015) 120–123

ﬁndings (Lardelli-Claret et al., 2011; Li et al., 2003; Massie et al.,
1995; Meuleners et al., 2006). As female drivers tended to accrueless mileage, as shown in Table 1, their driving experience andpatterns may differ from males’, which might have inﬂuenced theincidence, while the incidence might have been inﬂated by a “lowmileage bias”; i.e., low-mileage drivers have a heightened collisionrisk (Langford et al., 2006). More notably, the at-fault MVC
incidence of female drivers began to rise at an earlier age than formales. These ﬁndings imply the need to implement more gendersensitive safety measures. Female drivers were also found to be
more susceptible to injuries than males. This may be explained bygreater physical fragility (Evans, 2004; Li et al., 2003; Meuleners
et al., 2006) rather than MVC’s severity. MVC severity is another
determinant of injuries of female drivers that does not appear
higher than that of males in terms of injury risk to other vehicle
occupants in their MVCs.
To achieve a balance between older drivers’ safety and mobility,
it is also important to pursue further improvement of protective
measures in vehicle design. This is justiﬁed because, comparedwith teenage drivers, older drivers have a lower incidence of atfault MVCs based on the distance they drive but a higher injury risk
when they cause MVCs. Further, the number of older female drivers
with higher injury susceptibility is increasing, as mentioned above.
This challenge is especially pressing in rural areas wheretransportation alternatives are not readily available for older
adults.
Apart from safety measures for older drivers, our ﬁndings
reafﬁrm that more stringent safety policies are needed for young
drivers, who are actually much more likely to cause MVCs andinjuries to other vehicle occupants than older drivers. One possible
intervention is graduated driver licensing, a stepwise method of
increasing driving exposure to higher risk environments, as it has
proven effective in reducing collisions among novice drivers(Russell et al., 2011). Japan has not introduced this system.
The strength of the present study is its analysis considering
drivers’ responsibility for MVCs, showing the morbidity of injuries
in MVCs separately for responsible drivers and other road users,and focusing on MVCs during non-commercial driving to consider
the disproportionate amount of commercial driving in overall
driving across age groups. The at-fault MVC incidence was also
calculated based on non-commercial driving exposure, not on
population or licensed drivers. These considerations led to a more
valid comparison of driver safety by age.
Finally, we acknowledge several limitations of the study. First,
driving exposure may have been underreported (Taniguchi andFujii, 2006), but the results are still valid unless underreporting
varied between ages. Second, our analysis was limited to surveys ofcertain days of the week in certain months of the year. Therefore,
the ﬁndings may not be generalizable to a full year because of
possible daily and monthly variations in driving patterns, which
may also differ by age and sex. Third, older drivers may be

123overrepresented in MVCs because of their fragility, as mentioned
earlier. Despite that, older drivers were found to be less likely tocause MVCs than teenage drivers.
We conclude that older drivers had a lower risk of at-fault MVCs
per unit of travel than young novice drivers, but their collision risk
is higher than that of middle-aged drivers and increases as thedrivers’ age advances. Though the injury risk older drivers pose toothers in their at-fault MVCs is lower, their own risk of injury ishigh. As the number of older drivers is increasing, efforts to reduce
their at-fault MVCs appear justiﬁed.
Acknowledgement
This work was supported by the University of Tsukuba.
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