ITARDA

Institute for Traffic Accident
Research and Data Analysis（財）交通事故総合分析センター
ITARDA INFORMATION

No.

92

2012

JANUARY

Fatality rate (%)

0.7

The fatality rate for rear seat passengers,
by seat belt use/non-use
0.6

0.5

0.4

0.3

The fatality
rate for rear seatpassengers who were
not wearing seat belts wasapproximately

3.5

times that of thosewearing seat belts

With seat belt
non-use0.58 %

0.2

0.1

With seat belt use

0.165 %
0
Special feature

Characteristics of accidents
in which rear seat passengers
were not wearing seat belts~Wearing a seat belt increases safety 3.5-fold~Institute for Traffic Accident Research and Data Analysis

ITARDA
INFORMATION
財団法人 交通事故総合分析センター

イタルダ・インフォメーション

2012 JANUARY

92

No.

Special feature

Characteristics ofaccidents in which rearseat passengers were
not wearing seat belts

死亡率（%）

0.7

後席乗員シートベルト着用有無別の死亡率
0.6

0.5

0.4

0.3

後席シートベルト
非着用の死亡率は
後席シートベルト着用の

3.5

約

倍

0.2

0.1

0

シートベルト着用

0.165 %

シートベルト非着用

0.58 %~Wearing a seat belt
increases safety 3.5-fold~
The number of motor vehicle occupants killed
has been decreasing year on year, and has
been second to pedestrians since 2009, but
the level is still high.
Wearing a seat belt has the effect of lessening
the severity of injury suffered by car occupants
during accidents, yet the percentage of rearseat passengers who wear seat belts is lower
than those of drivers or front seat passengers.
The fatality rate for car occupants not wearing
seat belts is generally higher than that for car
occupants wearing seat belts, and in somecases the results were of huge importance;
this was equally true for rear seat passengers.
At the time of collision, if a rear seatpassenger is not wearing a seat belt, his or
her body will be sent flying in a forward
direction into the back of the seat in front orother places, which can result in major injury
or death. It can also increase the danger forthe driver or passenger seat passenger. The
passenger can also be thrown out of the car,resulting in death. In this issue of ITARDA
Information, we focus on the wearing of seatbelts by rear seat passengers and discuss thecharacteristics of related accidents.

CONTENTS

1 State of damage to car occupants
not wearing seat belts

2 Analysis of fatal accidents in whichrear seat passengers were notwearing seat belts

3 Examples of accidents
4 Summary/recommendations

特集

後席乗員がシートベルトを着用していなかった事故の特徴 〜着用で安全性3.5倍〜State of damage to car occupants
not wearing seat belts

CTION
SE

1

(1) The seat belt use rate based on the Traffic Accident Database
Fig. 1 shows the trends over the last five years inthe seat belt use rate of car occupants who wereinvolved in fatal accidents, by the car occupants’position in the car, based on the Traffic Accident
Database.
The cars included in the data were standardsized passenger cars (with no more than 11
seats), mini-sized passenger cars, standardsized trucks (no more than 5t in gross vehicle
weight) and light trucks, these comprising the
majority of registered vehicles. People involvedin accidents in the data were considered to berear seat passengers who were in the vehicles
of primary parties or secondary parties, whichmake up the majority of accidents. We analyzed
the data using these conditions.

Looking at Fig. 1, because the wearing of seatbelts in the rear seat was made mandatory inJune 2008, the seat belt use rate which had
been low up to that point ha s risen;
nevertheless, with the use rate of rear seatpassengers at approximately 60% by 2010, therate remains lower than the use rates of drivers
and passenger seat passengers.
Here, the seat belt use rate shows the rate ofcasualties who were wearing seat belts as apercentage of all casualties in traffic accidents.

Seat belt=
use rate (%)

Number of casualties who
were wearing seat belts
Total number of casualties

98.1%

100

96.0%

90

■
■
■

80

Seat belt use rate (%)× 100

Driver’s seat
Front seat
Rear seat

70
60
50

60.4%

2009

2010

47.1%

40
30

60.5%

31.4%

30.6%

2006

2007

20
10
0

2008

Fig 1: Trends in the seat belt use rate, by car occupants’ position in traffic accidents

92 ITARDA INFORMATION

3

特集

後席乗員がシートベルトを着用していなかった事故の特徴 〜着用で安全性3.5倍〜(2) Results of seat belt use in rear seats being made mandatory
Fig. 2 shows the trends in the numbers of rear seatpassengers who were killed or seriously injured
over the last five years, with the aim of confirming
the effects of rear seat belt use, which was mademandatory in June 2008.
The number of rear seat passengers who were
killed or seriously injured has been on adecreasing trend year on year, with the number offatalities and serious injuries decreasing comparedto the previous year by a considerable margin in
2008, allowing us to confirm that seat belt use
being made mandatory has indeed had an effect.
A considerable decrease was seen immediately
after seat belt use was made mandatory, but from2009 onwards the decrease has slowed down. If
we are to decrease still further the numbers offatalities and serious injuries, further educational
outreach concerning seat belt use is essential.

No. of fatalities and serious
injuries (No. of people)

2500
2250

2330
2216

2000
1920

1750
1500

2006

2007

2008

1859

1856

2009

2010

Fig. 2: Trends in the number of rear seat passengers killed or seriously injured(3) The seat belt use rate in fatal accidents
Table 1 and Fig. 3 show the figures for fatalities
categorized by whether or not the car occupants
were wearing seat belts, and their position in the carin terms of driver’s seat, front seat or rear seat, using

the Traffic Accident Database from 2010.
The seat belt use rate during fatal accidents was 53%
for drivers, 64% in the front seat and 30% in the rearseat, the lowest use rate of all the seats.

Table 1: Seat belt use rate of car occupants who were killed, by position in the car (2010)
Fatalities with seat belt Fatalities with seat beltuse (No. of people)
non-use (No. of people)

Driver’s seat

561

Front seat
Rear seat

Fatalities with seat belt use
unclear (No. of people)

Total fatalities(No. of people)

Use rate for fatal
accidents (%)

Non-use rate for fatal
accidents (%)

Use-unclear rate forfatal accidents (%)

474

34

1069

53

44

3

118

64

2

184

64

35

1

54

119

7

180

30

66

4

Unclear 4%
Unclear 3%

Did not wear
Wore aa seat belt 44% seat belt 53%

Driver’s seat fatalities
n=1069 people

Unclear 1%
Wore a seatbelt 30%

Did not wear
a seat belt 35%
Wore a seatbelt 64%

Front seat fatalities
n=184 people

Did not wear aseat belt 66%

Rear seat fatalities
n=180 people

Fig. 3: Seat belt use rates for fatalities, by position (2010)
4

ITARDA INFORMATION 92

(4) Risks of non-use in the rear seat
What degree of risk does non-use of seat belts
pose?
Table 2 and Fig. 4 compare the fatality rates andfatality and serious injury rates for rear seatpassengers, by whether or not people were
wearing seat belts, using the Traffic Accident
Database from 2010 as with the previous
section.
The fatality rate and fatality and serious injury
rate are defined as follows.
Fatality rate (%) =Fatality andserious injury
rate (%)=

No. of fatalities(No. of fatalities + no. of serious
injuries + no. of slight injuries)(No. of fatalities +no. of serious injuries)

× 100

× 100

(No. of fatalities + no. of serious
injuries + number of slight injuries)

The fatality rate is the rate of fatalities as apercentage of all casualties in traffic accidents. The
fatality and serious injury rate is the rate of fatalities
and serious injuries as a percentage of allcasualties in traffic accidents. For both, the higher
the rate the higher the risk is considered to be.
With a fatality rate of 0.58% for seat belt non-use
and of 0.165% for seat belt use, the rate for seatbelt non-use is approximately 3.5 times that forseat belt use.
With a fatality and serious injury rate of 5.69% forseat belt non-use and 1.88% for seat belt use, therate for seat belt non-use is approximately 3 times
that for seat belt use. This signifies that rear seatpassengers who do not wear seat belts are facinga high degree of risk.

Table 2: The fatality rate and fatality and serious injury rate for rear seat passengers,
by seat belt use/non-use
Fatalities(No. of people)

Serious injuries(No. of people)

Slight injuries(No. of people)

Total casualties(No. of people)

Fatality rate (%)

Fatality and serious
injury rate (%)

Seat belt use

54

562

32075

32691

0.165

1.88

Seat belt non-use

119

1049

19345

20513

0.58

5.69

NB: Cases where seat belt use was unclear are excluded from the table

0.6
0.5
0.4
0.3

0.58%

3.5-foldincrease

0.2
0.1
0

n=53,204 people

60.165%
Use

Non-use

Fatality rate for rear seat passengers

Fatality and serious
injury rate (%)

Fatality rate (%)

0.7

5.69%

5
4
3
2
1
0

3-foldincrease
1.88%
Use

Non-use

Fatality and serious injury rate for rear seat passengers

Fig. 4: Fatality rate and fatality and serious injury rate for rear seat passengers,
by seat belt use/non-use (2010)
The state of damage for rear seat passengers who were not wearing seat belts may be summarized
as follows.
● The seat belt use rate in the rear seat using the Traffic Accident Database is approximately 60%, well

below the rates for drivers (approximately 98%) and front seat passengers (96%). Many rear seatpassengers do not take seat belt use seriously, compared to drivers and front seat passengers.
● The number of fatalities and serious injuries for rear seat passengers is decreasing year on year. In 2008
in particular there was a considerable decrease in the number of fatalities and serious injuries comparedto the previous year. It can be confirmed from this that making the wearing of seat belts in rear seatmandatory is having an effect to a certain extent.
● The rate of seat belt non-use in the rear seat in fatal accidents was considerably lower than those fordrivers and front seat passengers, and rear seat passengers have a low level of awareness regarding
the wearing of seat belts.
● People who were not wearing seat belts had a fatality rate approximately 3.5 times higher than that ofpeople wearing seat belts, and a fatality and serious injury rate approximately 3 times higher,
representing a significant degree of damage.

92 ITARDA INFORMATION

5

特集

後席乗員がシートベルトを着用していなかった事故の特徴 〜着用で安全性3.5倍〜

CTION
SE

2

Analysis of fatal accidents in which rear seatpassengers were not wearing seat belts

The above analysis indicates that people who
were not wearing seat belts had a fatality rate
and fatality and serious injury rate higher thanthose who were wearing seat belts.
In this section, we will attempt to analyze thecomponent rate of seat belt use/non-use for rearseat passengers in terms of casualties in traffic
accidents using the Traffic Accident Databasefrom 2008~2010, in order to provide some hints
as to how to raise the seat belt use rate.

(1) The non-use rate for trucks is highFig. 5 is a graph showing the seat belt non-use
rate for standard-sized passenger cars, minisized passenger cars, standard-sized trucks andlight trucks.
The seat belt non-use rate is defined as follows.

Seat belt
non-userate (%)

No. of casualties withseat belt non-use=

Total no. of casualties

× 100

Overall, the seat belt non-use rate was higher fortrucks than for passenger cars. In particular, theseat belt non-use rate was highest of all for lighttrucks. Since loading of goods is prioritized in
cab-over vehicles, they are equipped with aloading platform, for which reason seat-belts are
sometimes not fitted in these vehicles so as tofacilitate easy-folding up of seats. It is believedthat this is one reason for the high seat belt nonuse rate in trucks. In addition, it is not mandatory
to fit seat belts in seats which are designed to
be folded up easily.

n=164,576 people
Average seat belt non-use rate: 42.2%
60

Non-use rate (%)

50
40

41.8%

40.5%

Standard-sized
passenger cars

Mini-sized
passenger cars

55.2%

55.5%

Standard-sizedtrucksLight trucks

30
20
10
0

Fig. 5: Seat belt non-use rate in the rear seat, by vehicle type [2008~2010]

6

ITARDA INFORMATION 92

(2) In fatal accidents or other traffic accidents which occur in the time slots around the nighttime andearly morning hours, the seat belt non-use rate is highFig. 6 is a graph showing the seat belt non-use
rate in the rear seat, by time period, divided into
two-hour slots. The seat belt non-use rate overthe 0~6 am period is high at around 56%, andin particular reaches a high point of 59% during
the 2~4 a.m. time slot. Conversely, the rate falls
to around 40% during the 8 a.m.~6 p.m. period.
This indicates that the seat belt non-use rate ishigher during nighttime and early morning hours
than during the daytime hours. Let us look at thetravel purposes of rear seat passengers during
these time slots.

Fig. 7 is a graph showing the seat belt non-use
rate in the rear seat, by time slot and by travel
purpose. The seat belt non-use rate for the timeslots around the nighttime and early morning
hours is higher across all travel purposes. In the
2~4 a.m. time slot in which the seat belt nonuse rate was particularly high, approximately
70% of journeys were made for the purposes ofdining or shopping, the highest level among all
items. Conversely, during daytime hours
approximately 60% of journeys were made forthe purpose of commuting to work/study, ahigher level than for other travel purpose items.
n=164,576 people

80

Non-use rate (%)

70
60
50

57.0%

59.0%

56.3%
46.6%

40
30

39.6%

38.4%

40.5%

38.6%

39.1%

8 a.m.
~10 a.m.

10 a.m.
~12 p.m.

12 p.m.
~2 p.m.

2 p.m.
~4 p.m.

4 p.m.
~6 p.m.

42.4%

50.7%

46.8%

20
10
0

12 a.m.
~2 a.m.

2 a.m.
~4 a.m.

4 a.m.
~6 a.m.

6 a.m.
~8 a.m.

6 p.m.
~8 p.m.

8 p.m.
~10 p.m.

10 p.m.
~12 a.m.

Fig. 6: Seat belt non-use rate in the rear seat, by time [2008~2010]
n=164,576 people

80

Work
Commuting towork/study■ Private: Trips/
pleasure
driving/visiting
hometown■ Private: Dining/
shopping■ Private:
Visiting/goingto hospital/
giving lifts/
other■Non-use rate (%)

■

70
60
50
40
30
0

12 a.m.
~2 a.m.

2 a.m.
~4 a.m.

4 a.m.
~6 a.m.

6 a.m.
~8 a.m.

8 a.m.
~10 a.m.

10 a.m.
~12 p.m.

12 p.m.
~2 p.m.

2 p.m.
~4 p.m.

4 p.m.
~6 p.m.

6 p.m.
~8 p.m.

8 p.m.
~10 p.m.

10 p.m.
~12 a.m.

Fig. 7: Seat belt non-use rate in the rear seat, by travel purpose and time [2008~2010]

92 ITARDA INFORMATION

7

特集

後席乗員がシートベルトを着用していなかった事故の特徴 〜着用で安全性3.5倍〜(3) Breakdown by age indicates that the seat belt non-use rate is lowest for passengers under 2, andhighest for those aged 16~24
Fig. 8 is a graph showing the seat belt non-use
rate in the rear seat, by age group. The seat belt
non-use rate for passengers under 5 is low, butrises steadily with increasing age between theages of 6 and 24. In particular, the seat belt nonuse rate for passengers aged 6~9 at 41.2%
represents a considerable increase from that forpassengers aged 3~5 (24.3%).
What is the situation regarding use of child seatsby passengers aged 6~9?
In general, it is said that a height of at least
135cm~140cm must be attained in order to beable to use an adult seat belt. The results of the
Ministry of Education, Culture, Sports, Scienceand Technology (MEXT)’s School Health Statistics
Survey of 2009 show that students attain a heightof at least 135~140cm after the 5th grade ofelementary school (aged 10). It may be said
therefore that passengers aged 6~9 also need touse child seats.
Let us analyze the situation regarding use of childseats by passengers under the age of 9.

Fig. 9 is a graph showing the child seat use rate
for passengers under 2, aged 3~5, and aged
6~9.
The child seat use rate is defined as follows.
Child seat
use rate (%)=

Total no. of casualties

n=164,576 people
Average seat belt non-use rate: 42.2%

50
40

41.2%

45.3%

48.4%

51.8%
44.4%

44.5%

25 to 44
years

Over
45 years

30
24.3%

20
10
0

12.7%
Under
2 years

3 to 5years

6 to 9years

10 to 12years

13 to 15years

16 to 24years

Fig. 8: Rear seat belt non-use rate, by age group [2008~2010]
Use unclear 1%

Adult seat belt
use 5%

Use unclear 2%

Use unclear 3%

Non-use24%

Passengers under 2n=10,594 people

Adult seat belt Child seat use
rate 60%
use 14%Passengers aged 3~5n=10,216 people

Non-use41%

ITARDA INFORMATION 92

Adult seat belt
use 46%

Passengers aged 6~9n=13,406 people

Fig. 9: Child seat use rate, by age group [2008~2010]8Child seat
use rate 10%

Non-use13%

Child seat use
rate 81%× 100

The child seat use rate is 81% for passengers
under 2 and 60% for passengers aged 3~5,
decreasing to 10% for passengers aged 6~9. It isbelieved that the rates are higher for passengers
under 5 because child seat use is mandatory forthis age group. In addition the seat belt use rate
for passengers aged 6~9 is approximately 56%,of which it is evident that 46% are using adult seatbelts. It is believed that most drivers andguardians lack adequate understanding of thephysical requirements necessary to be able touse an adult seat belt.

60

Non-use rate (%)

No. of casualties withchild seat use

(4) Why did passengers not use a seat belt?
Why do some passengers not use a seat belt
even though using a seat belt greatly decreases
the fatality rate? We attempted to investigate thereasons for seat belt non-use, using our in-depth
study database gathered at the Institute.
The reasons for seat belt non-use were clarified
for 74 passengers who had suffered traffic
accidents while not wearing seat belts in the rearseat (1993~2010).
Fig. 10 is a graph which divides the 74 passengers

into proportional categories by their reason for notusing a seat belt. “It is not a habit with me” formed
the largest proportion of reasons for not using aseat belt, followed by “It’s a nuisance/tedious” and“I won’t cause an accident/it’s only a short trip.”
Based on this, it is considered that passengers are
not taking the wearing of seat belts seriously
because of a strong belief that they will be all rightwithout wearing seat belts, not because they areunable to wear a seat belt.

I won’t cause an
accident/it’s only ashort trip
10 people/13%

It’s a nuisance/
tedious28 people/38%

It is not a habit
with me36 people/49%

Accidents in which reasons for non-use were ascertained [1993~2010](No. of rear seat passengers: 74)

Fig. 10: Reasons why passengers did not wear a seat belt [1993~2010]
The characteristics of fatal accidents or other traffic accidents in which rear seat passengers were notwearing seat belts may be summarized as follows.
● Among trucks, in car types with loading platforms where the seats are designed to be folded up

easily, such seats are sometimes not fitted with seat belts, meaning that rear seat passengers
cannot wear a seat belt even if they desire to do so.
● From the nighttime to early morning hours, passengers who do not wear a seat belt outnumber
those who do. In terms of travel purpose, approximately 70% of those traveling for dining/
shopping purposes during the 2~4 a.m. time slot in particular do not wear a seat belt, a higher
rate than for other travel purposes.
● Among passengers aged 6~9, only 10% use a child seat due to low awareness levels amongguardians, even though a child seat suited to their physical requirements is essential.
● Reasons for not wearing a seat belt were “It is not a habit with me,” “It’s a nuisance/tedious”
and “I won’t cause an accident/it’s only a short trip.” This shows that there is a strong belief
among such passengers that they will be all right without wearing seat belts, rather than an
inability to wear seat belts.

92 ITARDA INFORMATION

9

特集

後席乗員がシートベルトを着用していなかった事故の特徴 〜着用で安全性3.5倍〜

CTION
SE

3

Examples of accidents

Finally, we will present two examples of accidents which further exemplify the effects of rear seat belt
use, based on the Traffic Accident Database.
Case 1: Rear seat passenger thrown out of the car[Accident situation]
At around 7 p.m. on a sunny day, a man in his
30s was driving a car (A) (a standard-sized
passenger car) along a six-lane expressway.
When the driver for some reason changed
lanes, he made an error in operating thesteering wheel causing the car to skid
sideways, resulting in the front of the carcolliding at an estimated speed ofapproximately 75 km/h with a guard cablewhich had been laid out on the outside of theroad shoulder. Following this, the reboundforce of the collision span the car around in ananti-clockwise direction while simultaneously
flipping it over into the right-hand lane,
immediately after which another vehicle
collided with it from the rear; finally, the carcollided from the front with a guard rail which
had been laid out as a central divider.
[Seat belt use/injury situation]
In addition to the driver, the car (A) was also
occupied by a passenger in the passenger seat(a man in his 30s), a passenger in the right-handrear seat (a woman in her 60s) and a passenger
in the left-hand rear seat (a boy); the driver andpassenger seat passenger were wearing seatbelts, but neither rear seat passenger was
wearing a seat belt.
In this accident, the guard cable was sentcrashing through the glass of the driver’s seatwindow, resulting in injuries to the driver
including head injuries which caused his death.
The passenger seat passenger was uninjured.
At the time of the collision with the guard cablethe shock of the collision threw the right-handrear seat passenger out of the car through theright-hand rear seat window or the rear window;
she collided with the road surface resulting inheart/head injuries which killed her. It was
conjectured that had she been wearing a seatbelt, she could have avoided being thrown fromthe car and would not have been killed.
The left-hand rear seat passenger sufferedinjuries (slight injuries) in the form of brain
concussion as a result of colliding with the backof the seat in front at the time of the collision.

Diagram of the scene of the accident

Central divider/guard rail

A4
Other car 3

A5

Other car 2

A3
Guard cable

10

ITARDA INFORMATION 92

A2

A1

Other car 1

Case 2: Rear seat passengers uninjured or sustaining only slight injuries
because they were wearing seat belts[Accident situation]
At 2:00 am on a clear night, a man in his 20s
was driving a car (A) (a standard-sized
passenger car) around the leftward curve of aone-way road at an estimated speed ofapproximately 80~100 km/h. For some reason,
the car (A)’s driver did not completely follow
the left-hand curve and veered rightward
outside the road; the right-front side of the carcollided with a tree, after which the left-front
side also collided with a utility pole.
Seat belt use/injury situation
The car (A)’s driver had been driving withoutwearing a seat belt, but the car’s other occupants—the passenger in the passenger seat (a man in
his 20s), the passenger in the right-hand rear seat(a man in his 20s) and the passenger in the lefthand rear seat (a man in his 20s)— put on theirseat belts immediately prior to the collisionbecause they sensed the danger of the speed atwhich the car was travelling.
Because the driver in this accident was notwearing a seat belt, his body was sent forwardwith the shock of the collision, causing his head
to collide with the right-hand pillar of the car (A),resulting in his death.
The passenger seat passenger sustained a
sprain to the cervical vertebrae (slight injury) andthe right-hand rear seat passenger a thoracic
fracture (slight injury), while the left-hand rearseat passenger was uninjured. As the bodies of
all three had been restrained by seat belts, they
did not collide with the internal structure of the
car and escaped with slight or no injuries.

Diagram of the scene of the accident

A3
A4

A2

A1

92 ITARDA INFORMATION

11

CTIONSE

4

Summary/recommendations

Institute for Traffic Accident Research and Data Analysis

後席乗員がシートベルトを着用していなかった事故の特徴 〜着用で安全性3.5倍〜ITARDA INFORMATION

特集

イタルダ・インフォメーション

In order to reduce injuries caused by traffic accidents❶ Because wearing a seat belt cuts the fatality rate to approximately
1/3.5, and the fatality and serious injury rate to approximately 1/3,
drivers should not only wear their own seat belts but also encourageother occupants to wear theirs. Particular care is needed regarding
the time around nighttime and early morning hours.

❸ Rear seat belts have not been made mandatory in some trucks;
however, these should be fitted, as they can save passengers’ lives.

92

No.

発 行 （財）交通事故総合分析センター
発行月 平成 年 月 〒102 0083 東京都千代田区麹町6 6 麹町東急ビル 階❷ Children under the age of 9 need child seats suited to their
physical requirements. Drivers and guardians should use
appropriate child seats for children, even if this seems like a
nuisance. We should also conduct educational outreach on theimportance of child seats.

2012

JANUARY

24
1

-

-

5

事務局
〒102-0083 東京都千代田区麹町6-6 麹町東急ビル5階
TEL03-3515-2525 FAX03-3515-2519

つくば交通事故調査事務所〒305-0831 茨城県つくば市西大橋6 41-1
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