ITARDA 25th Work Shop Report

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2022
25th Presentation Session for Traffic Accident Investigations, Analysis, and Research

Aiming to Reduce Motorcycle-Fatality Accidents among Young Persons:
What Can Be Seen from Trends Regarding Helmet Separation
Ryusuke Kato
Senior Researcher, Research Division

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ITARDA 25th Work Shop Report

1. Trends and challenges regarding motorcycle accidents
In regard to motorcycle demand in recent years,

While occupying four-wheeler
While riding motorcycle
While riding bicycle
While walking

amid the impact of the COVID-19 crisis, theNumber of fatalities

usefulness of motorcycles for applications such as
mobility and leisure has been becoming
increasingly recognized. The number ofmotorcycles sold in Japan in FY2020 stood at
371,000 units, marking a slight increase from
358,000 units in FY2019(1), and thus it seems that

FiscalYear

going forward motorcycles will continue to be usedFig 1. Trend regarding number of fatalities(2011 to 2020)

as a convinent means of transporation and as
vehicles for leisure purposes. Meanwhile, over themotorcycle accidents has generally been in adecreasing trend, with the number at 526 in
FY2020 (Figure 1), the fatality ratio (number of

While occupying four-wheeler
While riding motorcycle
While riding bicycle
While walking

Fatality ratio (%)

past 10 years, although the number of fatalities infatalities/number of casualties) has been in an
increasing trend. (Figure 2) Challenges with

FiscalYear

Fig 2. Trend regarding fatality ratio(2011 to 2020)

regard to further decreasing fatalities seem to(Figure 3), andanalysis and our observations in this regard.

Ages 90 to 94

Ages 85 to 89

Ages 80 to 84

Ages 75 to 79

Ages 70 to 74

Ages 65 to 69

Ages 60 to 64

Ages 55 to 59

Ages 50 to 54

Ages 45 to 49

Serious injury ratio (%)

Fatality ratio, n = 6,353
Serious injury ratio, n = 99,570

Fatality ratio (%)

During the period of 2011 to 2020, overall,Age groupFig 3. Number of motorcycle fatalities by age group(2011 and 2020 )separation. Below we introduce the results of this

2. Trends regarding young persons

Ages 40 to 44

during accidents, and the status of helmet

Ages 35 to 39

trends regarding the speed of young persons

Ages 30 to 34

regarding these challenges, placing a focus on

Ages 25 to 29

report, we have carried out factor analysis

Ages 20 to 24

accidents occurs in around 30% of cases. In thisAges 16 to 19

the fact that helmet separation during fatality

Number of fatalities

persons (ages 16 to 24) is highNumber of motorcycle fatalities
per 1,000 people of population2011 number of motorcycle fatalities per 1,000 people ofpopulation
2020 number of motorcycle fatalities per 1,000 people ofpopulation2011 motorcycle fatalities (n = 855)
2020 motorcycle fatalities (n = 526)

include the fact that number of fatalities of young

situation by age group, it is clear that both ofAges 72 to 73

Ages 68 to 69

Ages 64 to 65

Ages 60 to 61

Ages 56 to 57

Ages 52 to 53

Ages 48 to 49

Ages 44 to 45

Ages 40 to 41

Ages 36 to 37

Ages 32 to 33

Ages 28 to 29

were in decreasing trends, and looking at theAges 24 to 25of fatalities per 1,000 people of the population,

Ages 20 to 21

Ages 16 to 17

the number of fatalities, along with the number

Age group

Fig 4. Motorcycle fatality &serious injury ratio by age group (2012 to 2021)

these are high among young persons (ages 16 to24). (Figure 3)
Looking at the fatality & serious injury ratio (the percentage of these among the number of casualties) by age
group, “generally the tolerance of the human body declines as age increases,” so the fatality & serious injury ratio
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ITARDA 25th Work Shop Report

to-21 and 22-to-23 age groups and then decreases.
(Figure 5)
Furthermore, looking at the persons involved in
motorcycle accidents (primary parties and secondaryparties) by age group, the number of speed-limit

Number of violators during accidents(primary parties + secondary parties)

during fatality & serious injury accidents (2012 todecreases, there is a trend in which it peaks at the 20-violators is large among young persons (ages 16 tois more common among young persons comparedwith other age groups. As such, it seems that thenumber of fatalities is greater due to a higher risk ofAges 76 to 77

Ages 72 to 73

Ages 68 to 69

Ages 64 to 65

Ages 60 to 61

Ages 56 to 57

Ages 52 to 53

Fig 6. Number of motorcycle speed-limit
violators by age group (2012 to 2021)
Fatalities, n = 5,888

Helmet separation rate (%)

that driving at high speeds during motorcycle driving

Ages 48 to 49

Ages 44 to 45

Speed-limit violations, n = 3,172

24). (Figure 6)
Based on the above results, it can be presumed

Age group

Fig 5. Weighted average of danger-recognition
speed by age group (2012 to 2021)

weighted average of the danger-recognition speed2021) appears to be in a trend of increasing as age

Ages 40 to 41

correlation with the degree of injury. Although theAges 36 to 37

at the time of the accident, which has a highAges 32 to 33

Next, we will look at the relationship with speed

Ages 28 to 29(Figure 4)

Ages 24 to 25

reverse is true and there appears to be an increase.

Ages 20 to 21

under-20 age group with the 20-to-21 age group, theAverage speed at time of serious injury, n = 99,570

Ages 16 to 17

regarding persons age 20 and above, comparing theAverage speed at time of fatality, n = 6,353

Weighted averageof danger-recognition speed (km/h)

rises with age. Although this trend can be seen

injury accompanying higher speeds, and a higher
risk of unsuitable steering operations and so on.

Age group

Fig 7. Helmet separation rate by age group(2012 to 2021)

Nevertheless, among young persons, the 16-to-19
age group has the highest number of fatalities in

Non-wearing

proportion to the population (Figure 3), and a higher

2019

2017

2015

2013

2011

2009

2007

noticed a relationship with helmet separation.

2005

1995

of the 16-to-19 age group. As a result of this, we2003

the abovementioned circumstances as characteristics

2001(Figure 5). We carried out factor analysis, viewing

1999

weighted average of danger-recognition speed is low

1997

22-to-23 age groups (Figure 4). Meanwhile, theComposition ratio (%)

fatality & serious injury ratio than the 20-to-21 andWearing & non-separation
Wearing & separation

FiscalYear

Looking at the relationship between helmet

Figure 8. Trend regarding helmut wearing status(1995 to 2020)

separation rate(a) and age group, there is a trend in3

ITARDA 25th Work Shop Reportwhich this is high among young persons, followed byHelmet separation rate at time of fatalities,n = 2,766

Helmet separation rate (%)

elderly persons, and is the highest regarding the 16to-19 age group (Figure 7). During accidents, helmet
separation increases the chance of head injuries, andthus this trend seems to be one factor among theabovementioned characteristics of the 16-to-19 age
group. At the same time, this trend seems to beconnected with the fact that the number of fatalities is

Type-1
motorcycle

high among young persons.

Type-2
motorcycleLight
motorcycle

Compact
motorcycle

Figure 9. Helmet separation rate by vehicle type(2016 to 2020)

3. Factors regarding helmet separation and effects of countermeasures
In the previous chapter, we showed the helmet separation rate by age group, and below we will cover thegeneral situation regarding helmet separation during accidents. Looking at the composition ratio of helmet“wearing & non-separation” during motorcycle-fatality accidents over the past 25 years, there was an increase
from 52% in 1995 to approximately 65% in 2020. Meanwhile, “non-wearing” stood at 11.8% in 1995 and thenwas in a decreasing trend, and in recent years, it has declined to around 2%. Nevertheless, “wearing & separation”
hovered at around 30% throughout the 25-year period. (Figure 8) The results of our analysis regarding the various
factors related to helmet “wearing & separation” are shown below.
3-1. Vehicle type & danger-recognition speed
Helmet separation rate (%)

Looking at the situation by vehicle type, the helmet
separation rate was the highest regarding type-1
motorcycles, and the separation rate decreased as theengine-displacement volume of the vehicle typeincreased. (Figure 9) As for the helmet separation rate
relative to the danger-recognition speed, although we

Helmet separation rate, n = 2,541

predicted that the separation rate would increase inproportion to the speed due to a rise in the impact force

danger-recognition speed (km/h)

during accidents, the rate was higher regarding theFigure
10. Helmet
separation
rate by danger-recognition
speed
Figure10. Helmet
separation
rate by danger-recognition speed(2016 to 2020)

lower speeds than the higher speeds, and was at thehighest regarding the low speed of “20 km/h or below.”(Figure 10)aPercentage of cases in which a helmet was being worn
during an accident but became separated from the wearer
due to the impact of the accident
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3-2. Helmet shape
Within the accident data of the Tokyo Metropolitan Police Department(b), type of helmet shape is recorded, andusing this, we confirmed trends regarding helmet separation rate during fatality accidents by helmet shape in 2011
to 2020. Figure 11 shows a comparison of the separation rates of three types of helmet shapes (Chart 1) during
motorcycle-fatality accidents. It can be seen that the separation rate of half cap-type helmets is more than 20
points higher than that of the other full face-type and open face-type shapes. (Figure 11)3-3. Status of chin strap fastening

Full face-type

Open face-type

Full face-type, n = 164
Open face & jet-type, n = 131
Half cap-type, n = 93

Helmet separation rate (%)

Chart 1. Helmet shape

Half cap-type

Factors that affect helmet separation seem to include
how the helmet is being worn on head, and the status

Helmet typeof the fastening of the chin strap. The Tokyo

Figure 11. Separation rate by helmet shape(Tokyo Metropolitan Police Department,2011 to 2020)
Not fastened,
2021
4.3%

Metropolitan Police Department has implemented a survey
in which it interviewed motorcycle users regarding their“status of helmet chin-strap fastening” (n = 3,202 people,2021) (2). It appears that in 2021, approximately 27% ofmotorcycle users had a status in which theirchin strap was not properly fastened (was not fastened, orNot fastened
23.1%

was loosely fastened). (Figure 12)

Properly fastened
72.6%

As for factors related to helmet separation, the trends
seem to be related to age, vehicle type, speed, helmet
shape, and chin-strap status. Based on this, we envisioned
a specific type of case in which “a person of a younger age
group (or an elderly person) travels short distances on aFigure 12. Interview survey on chin straps(Tokyo Metropolitan Police Department, 2021)

type-1 motorcycle while wearing a half cap-type helmet,

Fatality ratio of wearing & separation

which is considered to be easy to put on, and does notproperly fasten the chin strap.”
3-4. Helmet separation risk and estimated reduction infatalities

Fatality ratio (%)

Fatality ratio of wearing & nonseparation

During helmet separation, there is a high possibility tohead injuries, so in order to check the danger of such, we

Head injuries n = 13,789

Fig 13. Fatality ratio according towhether there was helmet separation
With head as main part of body injured(2016 to 2020)bThis is accident data of the Tokyo Metropolitan Police Department and not national accident data.
5ITARDA 25th Work Shop Reportsought to find out fatality risk based on fatality ratios

Helmet: unknown wearing status
Helmet: non-wearing
Helmet: wearing & unknown separation status
Helmet: wearing & non-separation
Helmet: wearing & separation

Number of fatalities(number of fatalities/number of casualties) during head
injuries in accordance with whether there was helmet
separation. The various fatality ratios are shown in
Figure 13. During fatality accidents, the ratio of thecomposition ratio of “wearing & separation” in the casethat there was separation, to the composition ratio of“wearing & non-separation” in the case that there wasnon-separation (fatality risk ratio), was 18.68 / 5.35 =Main part of body injured, n = 526

3.49, and thus it appears that when there is helmet
separation, the fatality risk is approximately 3.5 times higher.

Fig 14. Number of fatalities by main partof body injured (FY2020)

Next, taking into consideration the abovementioned fatality
risk ratio, we estimated the fatality reduction effects in the case that helmet separation has been eliminated. We set
the conditions as follows.
・ If helmet “wearing & separation” is prevented, the “head” is protected, and thus the number of fatalities inwhich the main part of the body injured is the “head” has the same fatality composition ratio as with“wearing & non-separation.”
Reduction effects are sought based on the number of fatalities separated by the main part of the body injured in
motorcycle-fatality accidents in FY2020 (Figure 14).
• Total number of motorcycle fatalities in FY2020: 526• Number of fatalities in which there was helmet “wearing & separation” and the main part of the body injured
was the “head”: 87• Fatality risk ratio regarding “head” when there is helmet “wearing & separation”: 3.49
The number of fatalities in which there was “wearing & separation” and the main part of the body injured was
the “head” was 87. Based on the fatality risk ratio, it can be presumed that if there was no helmet separation inthese cases, 87 × (1 - 1/3.49) = 62.1 of the fatalities would not have occured. As a result, the number of fatalities
in 2020 would have been 464, which corresponds with a reduction of approximately 12%.
4. Conclusion
With the aim of reducing motorcycle-fatality accidents, we analyzed accident trends regarding young persons,factors related to helmet separation, and so on, and confirmed the following.
1.

Among young persons (ages 16 to 24), the weighted average of danger-recognition speed during accidents ishigh, and at the same time, the number of speed-limit violations is large. Thus, it can be presumed that there
is a situation in which travel speeds are high, so there seems to be a high risk of injuries during accidents.
Therefore, it appears that in order to reduce fatalities, measures for decreasing speeds during accidents, suchas reducing speed-limit violations, are essential.

2.

Among trends related to helmet separation, we identified various characteristics regarding age, vehicle type,
danger-recognition speed, and helmet shape, as well as the status of helmet chin-strap fastening, and thetrends appeared to include a high helmet separation rate among young persons. Furthermore, we showed that6ITARDA 25th Work Shop Reportby preventing helmet separation, it would be possible to reduce the number of accident fatalities of all age
groups by up to 12%.
In order to prevent helmet separation, it is important to wear a helmet of the proper size and fasten the chinstrap. It seems that reducing helmet separation will require ongoing awareness-raising activities targeting drivers.
At the same time, based on the fact that over the past 25 years the separation rate during fatality accidents has
hovered at 30%, it seems that one way to reduce motorcycle-fatality accidents will be to consider new policies for
improving the situation, which could include taking legal measures.
<Acknowledgments >We would like to express our appreciation to the Tokyo Metropolitan Police Department for its providing us withdata on motorcycle accidents from 2011 to 2020.
<Citations & references>(1) Japan Automobile Manufacturers Association, FY2021 motorcycle market trend survey:
https://www.jama.or.jp/release/news_release/2022/1300/(2) Tokyo Metropolitan Police Department webpage:https://www.keishicho.metro.tokyo.lg.jp/kotsu/jikoboshi/nirinsha/heru_pro.html

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