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ITARDA INFORMATION
交通事故分析レポート No.129lSpeciafeatureMotorcycle accidents on expressways

4,000

The number of fatalities on
expressways has not declined

35

3,500

30

3,000

25

2,500

20

2,000
The number of fatalities on ordinary
roads has dropped to roughly 1/4

15
10
5

500

No. of fatalities
on ordinary roads

2017

2016

2015

2014

2013

2012

2011

Composition rateof fatalities on expressways

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

No. of fatalities
on expressways

1998

1997

1996

1995

1994

0

1993

1,000

1992

The composition rate for the number of fatalities
on expressways out of the total has risen roughly
3.6-fold in these past 27 years!
1991

0

1,500

No. of fatalities on ordinary roads (people)

40

1990

No. of fatalities on expressways (people)/
Composition rate (%)~ The number of fatalities among motorcycle riders
on expressways has not declined ~Fig. 1. Trends in the number of fatalities among motorcycle riders
on expressways and ordinary roads (1990 - 2017)

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・P2
1 Introduction ・
Vehicle-vehicle accidents between motorcycles
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and four-wheel vehicles on expressways
Characteristics of accidents involving a motorcycle
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3
going straight and a four-wheel vehicle changing lanes
4 Introducing and considering an accident case example ・
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5 Conclusion ・lSpeciafeatureMotorcycle accidents on expressways~ The number of fatalities among motorcycle riders on expressways has not declined ~1 Introduction
The total number of fatalities from traffic accidents that had surpassed 10,000 people in the early half of the 1990s
has fallen below 4,000 people in recent years. The number of fatalities from accidents involving people riding
motorcycles (including the total from both mopeds and automatic motorbikes) is similar, in that the number had
been in excess of 2,000 people in this same time period, but has recently fallen to around 600 people (Fig. 2).

No. of fatalities (people)

12,00010,000
8,000
6,000
4,000
2,000

Walking

2017

2016

2015

2014

2013

Ridinga bicycle, etc.

2012

2011

2010

2009

2008

2007

2006

2005

2004

Ridinga motorcycle

2003

2002

2001

2000

1999

1998

1997

Riding in afour-wheel vehicle

1996

1995

1994

1993

1992

1991

1990

0

Total

Fig. 2. Trends in the number of traffic accident fatalities (1990 - 2017)
However, looking at the number of fatalities while riding on a motorcycle by ordinary roads and expressways
reveals that whereas there has been a clear downward trajectory in the number of fatalities on ordinary roads, thenumber of fatalities on expressways (national expressways and designated motorways) has fluctuated up anddown. Yet compared with the early 1990s, there is no longer a clear downward trajectory with this (Fig. 1).

10.0

0.0

0.0

No. of fatalities/
1,000km in total extensions

No. of casualties/1,000km in total
extensions (persons/1,000km)

1.0
2017

20.0

2016
2015

2.0

2014
2013

30.0

2012
2011

3.0

2010
2009

40.0

2008
2007

4.0

2006
2005

50.0

2004
2003

5.0

2002
2001

60.0

2000
1999

6.0

1998
1997

70.0

1996
1995

7.0

1994
1993

80.0

1992
1991

8.0

1990

No. of fatalities/1,000km in total
extensions (persons/1,000km)

However, this is backed by the fact that the total extensions to expressways have been growing longer year by
year. As such, when you look at the number of fatalities while riding motorcycles per the total extensions you seethat while this downward trajectory has persisted, in recent years it has been holding steady, with the number ofcasualties (comprised of the total number of fatalities and injuries) continuing to trend downward. It also suggeststhat the risk of accidents is not growing (Fig. 3).

No. of casualties/
1,000km in total extensions

Fig. 3. Trends in the number of fatalities/casualties while riding motorcycles
per total length of extensions to expressways (1990 - 2017)
ITARDA INFORMATION no.129

ITARDA INFORMATION no.129
Expressways are inherently organized in a manner that makes accidents difficult to happen, such as the fact thatthey are not travelled by pedestrians or bicyclists, and because they lack intersections. Looking at the types ofaccidents indicates that of the 148 people who died while riding a motorcycle over the five-year period from 2013
to 2017, a majority at roughly 60% died due to single-vehicle accidents. As opposed to this, of the 1,684 casualties
over this same period, roughly 70% were due to vehicle-vehicle accidents (Fig. 4).

No. of fatalities (n = 148 people)

No. of casualties (n = 1,684 people)

Pedestrian-vehicle

Pedestrian-vehicle0％0％Single-vehicle

29％

Vehicle-vehicle

Vehicle-vehicle

42％

Single-vehicle

71％

58％

Fig. 4. Composition rate for the types of accidents involving fatalities/casualties
while riding a motorcycle on expressways (total from 2013 - 2017)

In terms of the other parties to vehicle-vehicle accidents involving motorcycles on expressways, four-wheel
vehicles (FWV) account for the vast majority in terms of both the number of fatalities and casualties (Fig. 5).

Vehicle-vehicle:
No. of fatalities (n = 55 people)

Vehicle-vehicle:
No. of casualties (n = 1,091 people)
Motorcycle-other

3％

Motorcycle-motorcycle

6％Motorcycle-FWV

100％

Motorcycle-FWV

91％

Fig. 5. Composition rate for the other party for fatalities/casualties from vehicle-vehicle accidents
while riding a motorcycle on expressways (Party 1 and 2; total from 2013 - 2017)
Therefore, this issue will focus on vehicle-vehicle accidents between motorcycles and four-wheel vehicles on
expressways out of a desire to analyze what sorts of characteristics these accidents have.
ITARDA INFORMATION no.129

lSpeciafeatureMotorcycle accidents on expressways~ The number of fatalities among motorcycle riders on expressways has not declined ~Vehicle-vehicle accidents between motorcycles

2 and four-wheel vehicles on expressways

Since expressways are organized in a manner where they lack intersections, with the exception of service areas(SA) and parking areas (PA), they are essentially free of occurrences of accidents like crossing collisions andcollisions between a vehicle turning right and a vehicle going straight. Rather, accidents caused by the mutual
movement of multiple vehicles traveling in the same direction account for the majority of such accidents. Thismutual type of movement (movement pattern) for vehicle-vehicle accidents between motorcycles and four-wheel
vehicles was analyzed using the number of casualties from Parties 1 and 2.
The most common accident type involved a motorcycle going straight and a four-wheel vehicle changing lanes,
which accounted for 35% of the total. The second most common type involved both the motorcycle and four-wheel
vehicle going straight (its composition reveals that rear-end collisions accounted for more than three-fourths of thetotal) at 25%. Other patterns aside from these two accounted for a relatively small number (Fig. 6).

Vehicle-vehicle (n = 988)

Composition rate (%)

50
40
30
20
Other

10

Going straight0

S

Type of movementby the FWV

Going slow/stopping

p

gu

in
tart

s
ane

gl

gin

n
Cha

/ov

ing

s
Pas

Passing/overtaking

ing

k
erta

Goi

n

o
g sl

ng

ppi

to
w/s

ng

Goi

s

Changing lanes

t

gh
trai

er

Oth

Starting up

Type of movementby the motorcycle

Fig. 6. Composition rate for the type of movement for casualties from vehicle-vehicle accidents
between a motorcycle and a four-wheel vehicle on expressways(Party 1 and 2; total from 2013 - 2017)
Based on the number of casualties indicated in Fig. 6 and from the fact that vehicle-vehicle accidents between a
motorcycle and a four-wheel vehicle accounts for 91% of the total number of vehicle-vehicle accidents involving
motorcycles, the percentage of accidents involving a motorcycle going straight and a four-wheel vehicle changing
lanes accounts for roughly one-third of the total number of vehicle-vehicle accidents involving motorcycles.

Characteristics of accidents involving a motorcycle

3 going straight and a four-wheel vehicle changing lanes
When it comes to the most common accident pattern of a motorcycle going straight and a four-wheel vehicle
changing lanes, these were analyzed with respect to what sorts of accidents this resulted in (type of accident),
what caused them (human factors), and what speeds the vehicles were traveling at (danger perception speed).
The results of this are indicated below.
ITARDA INFORMATION no.129

ITARDA INFORMATION no.129■ Trends with the types of accidents
In cases where an accident occurred due to a
motorcycle going straight and a four-wheel vehicle
changing lanes, most of these cases resulted incollisions and contact accidents, while only asmall number resulted in rear-end collisions,despite still being present (Fig. 7).
While rear-end collisions are a subcategory undercollisions and contact accidents, here a distinction
will be drawn in which collisions and contact
accidents are to be read as excluding rear-end
collisions.

Motorcycle going straight andFWV changing lanes (n = 350)
Rear-end collisions

Other

6％

32％

Collisions/contact accidents

62％

Fig. 7. Composition rate for the type of accident involving casualties while riding a motorcycle
in cases involving a motorcycle going straight and a four-wheel vehicle changing lanes(Party 1 and 2; total from 2013 - 2017)

Composition rate (%)

Human factors for motorcycles
100
90
80
70
60
50
40
30
20
10
0

Causedrear-end
collision（n＝11）

Suﬀeredrear-end
collision（n＝9）

Collision/contact
accident（n＝217）

Other
Vehicle-vehicle（n＝113）
accident
total（n＝350）
Failure to pay attention
forward (external)

Failure to conﬁrm
safety factors

Failure to pay attention
forward (internal)
Failure to observe surrounding
traﬃc movement

Traﬃc environment

Operating error

UnsurveyableNo human factor

Prediction error

Human factors for FWV

Composition rate (%)■ Trends with human factors
Tr e n d s w i t h t h e h u m a n f a c t o r s a m o n g
motorcycle drivers and four-wheel vehicle
drivers differ for rear-end collisions and otheraccident types.
Characteristic factors that could be mentioned
for rear-end collisions are the fact that there
were “No human factors” with motorcycles
c ausing rear- end c ollisions, but that with
four-wheel vehicles that suf fered rear- endcollisions there was frequently a “Failure toconfirm safety factors” (where the driver failed toconf irm safet y, or did so inadequately). In
ordinar y cases, it is rare for there to be no
human factors on the side causing the rear-end
collision and human factors on the side sufferingsuch collisions, and so rear- end collisions
caused by a motorcycle going straight and afour-wheel vehicle changing lanes could be
described as a special case.
For other accident types aside from rear-end
collisions, there were no human factors on the
motorcycle side roughly half the time. Of thesehuman factors, “Failure to observe surrounding
traffic movement” (where the driver was awareof the presence of the other party to theaccident, but neglected to observe themcarefully due to the belief that there was no
danger) accounted for the majority of cases. In
addition, “Failure to confirm safety factors”
accounted for the majority of cases with
four-wheel vehicles (Fig. 8).

100
90
80
70
60
50
40
30
20
10
0

Suﬀeredrear-end
collision（n＝11）

Causedrear-end
collision（n＝9）

Collision/contact
accident（n＝217）

Other
Vehicle-vehicle（n＝113）
accident
total（n＝350）
Failure to pay attention
forward (external)

Failure to conﬁrm
safety factors

Failure to pay attention
forward (internal)
Failure to observe surrounding
traﬃc movement

Traﬃc environment

Operating error

UnsurveyableNo human factor

Prediction error

Fig. 8. Composition rate for human factors among the casualties of motorcycle riders
in accidents involving a motorcycle going straight and a four-wheel vehicle changing lanes(Party 1 and 2; total from 2013 - 2017)
ITARDA INFORMATION no.129

lSpeciafeatureMotorcycle accidents on expressways~ The number of fatalities among motorcycle riders on expressways has not declined ~

〜140

〜120

〜100

〜90

〜80

〜70

〜60

〜50

〜40

Danger perception speed
for the FWV changing lanes (km/h)

〜30

〜20

〜10

20
18
16
14
12
10
8
6
4
2
0

StoppedComposition rate (%)■ Trends with the danger perception speed
The speed at which the parties were traveling when they perceived that there was the danger of an accident
occurring is referred to as the danger perception speed. A graphical representation of the combined danger
perception speeds of motorcycles and four-wheel vehicles is shown in Fig. 9.
This reveals that two types of situations account for the majority of situations in which accidents involving a
motorcycle going straight and a four-wheel vehicle changing lanes occur:(1) Situations in which a motorcycle is overtaking a four-wheel vehicle traveling at low speeds(2) Situations in which a motorcycle is traveling parallel to or overtaking a four-wheel vehicle traveling normally.

〜140
〜120
〜100
〜90
〜80
〜70
〜60
〜50
〜40
〜30
〜20
〜10
StoppedDanger perception speed
for the motorcycle
going straight (km/h)

Fig. 9. Composition rate for the danger perception speed among the casualties of motorcycle riders
in accidents involving a motorcycle going straight and a four-wheel vehicle changing lanes(Party 1 and 2; total from 2013 - 2017)■ Conceivable typical accident scenarios
Typical accident scenarios derived from the trends concerning the danger perception speed and human factorsthat could be mentioned include:(1) For situations in which a motorcycle is overtaking a four-wheel vehicle traveling at low speeds- Accidents involving a motorcycle traveling down an open lane next to a column of traffic due to congestion
without paying sufficient attention to the movement of the vehicles stuck in said congestion colliding with afour-wheel vehicle changing lanes without noticing the motorcycle- Accidents involving a motorcycle traveling between lanes or on the road shoulder that is not acknowledged
under ordinary circumstances and without paying sufficient attention to the movement of vehicles stuck incongestion and a four-wheel vehicle changing lanes without noticing the motorcycle(2) For situations in which a motorcycle is traveling parallel to or overtaking a four-wheel vehicle traveling normally- Accidents involving a motorcycle traveling or overtaking another vehicle without paying sufficient attention to
the movement of the surrounding vehicles and a four-wheel vehicle changing lanes from the next lane
without realizing that a motorcycle was present
In order to avoid theseThe drivers of motorcycles should:- Pay attention to the movement of vehicles in surrounding lanes even when going straight ahead in their own
lane- Operate based on the assumption that they have not been noticed by the drivers of the surrounding vehicles- Refrain from weaving through traffic in between lanes or on road shoulders- Refrain from overtaking other vehicles when there is a large difference in their speeds
As for the drivers of four-wheel vehicles:- Soundly checking for the presence of motorcycles behind them and to their side when changing lanes would
presumably be an effective approach to this

ITARDA INFORMATION no.129

ITARDA INFORMATION no.129

4 Introducing and considering an accident case example
Roughly 60% of accidents involving a motorcycle going straight and a four-wheel vehicle changing lanes end up
being collision or contact accidents. However, there are also cases aside from these that cannot be classified asrear-end collisions or any other type. One example of an accident where a motorcycle rear-ended a four-wheel
vehicle because the four-wheel vehicle carelessly changed lanes will be taken up by touching on the causes
leading to the accident and the conceivable possibilities derived therefrom.

■ Accident case example: Case involving a motorcycle rear-ending a four-wheel vehicle

changing lanes

In the morning of a clear day, Mr. A (motorcycle/over 1,000 cc) was traveling at roughly 100 km/h in the second
lane of an expressway with three lanes in each direction. At the same time, Mr. B (large truck) was traveling at
roughly 85 km/h ahead of Mr. A. Even though Mr. A was riding in the second lane, he planned to change lanes tothe third lane as he drew close to Mr. B, who was driving at a slower speed than his own, in an attempt to overtake
Mr. B. However, there was a series of several passenger vehicles in the third lane that was also passing Mr. B.
Therefore, Mr. A waited for these vehicles to pass before changing lanes to the third lane, where he accelerated toover 100 km/h in order to pass Mr. B, following along with the vehicle ahead of him.
However, when Mr. B, who had been traveling in the second lane, wanted to change lanes to the third lane in aneffort to overtake a dump truck traveling at a slower speed than himself, he noticed that a number of passenger
vehicles were moving at considerable speed from farther back in the third lane. So he waited for them to pass
before changing lanes. However, Mr. B failed to notice that Mr. A was coming after a group of said passenger
vehicles. Realizing that the lane was now blocked off, Mr. A applied the brakes, but was unable to do so in timeand ended up getting into a rear-end collision with the back of Mr. B’s large truck. The front part of Mr. A’s
motorcycle suffered severe damage, and Mr. A suffered serious injuries as well (Fig. 10).

Central median strip

B2

A2
A1
B1

Dump truck
Road shoulder

Fig. 10. Example of a four-wheel vehicle rear-ended by a motorcycle when changing lanes■ Assumed causes and considerations
The human factor that led Mr. A (motorcycle/caused the rear-end collision) to get into the accident could beconsidered a failure to observe surrounding traffic movement. Despite realizing that a large truck was travelingahead of him, he neglected to pay attention due to a failure to recognize the hidden danger. As such, it could bepointed out that he was unable to adequately decelerate or take evasive action when Mr. B changed lanes.
The human factor on the part of Mr. B (large truck/suffered the rear-end collision) could be considered a failure toconfirm safety factors. It could be pointed out that he failed to recognize Mr. A coming at the end of a group ofpassenger vehicles that were passing by in the third lane. Since he changed lanes under such conditions, thisultimately resulted in him interfering with Mr. A’s forward passage.

ITARDA INFORMATION no.129

- The number of fatalities from accidents while riding a motorcycle on expressways has notdecreased that much compared with the number from the first half of the 1990s- Whereas roughly 60% of single-vehicle accidents end up being accidents involving the death of
a motorcycle rider, roughly 70% of vehicle-vehicle accidents result in casualties- Vehicle-vehicle accidents frequently involve cases where an accident occurs when a four-wheel
vehicle changes lanes while a motorcycle is going straight- The major causes for this are estimated to be a failure to confirm safety factors whenfour-wheel vehicles change lanes, insufficient attention paid by motorcyclists, and motorcyclists
weaving between vehicles and traveling on the road shoulder that are not acknowledged underordinary circumstances
The drivers of motorcycles should strive to not weave between vehicles and drive on the roadshoulder, make every effort to notice the movement of vehicles in the next lane over when they are
traveling down an empty lane, and refrain from driving with substantial speed differences with othervehicles, among other efforts, while the drivers of four-wheel vehicles should soundly check to
confirm safety with the awareness that motorcycles could be coming up from behind them when they
are changing lanes, so as to reduce the number of accidents with motorcycles on expressways.
(Hamada Shinji)

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ITARDA INFORMATION no.129

つくば 交通事故調査事務所

住 友 水 道 橋 ビル８ 階

イタルダインフォメーションに関するお問い合せ先No.129

公益財団法人 交通事故総合分析センター
令和元年5月 〒101 0064 東 京 都 千 代 田 区 神 田 猿 楽 町 ２ ７ ８Compared with ordinary roads, expressways allow drivers to quickly and safely travel the same
distance with minimal effort. However, traffic accidents do occur on them, albeit rarely, and they carry
the potential to produce serious accidents as a result of the fact that vehicles travel at high speeds.

ITARDA INFORMATION

5 Conclusion

交通事故分析レポート

With rear-end collisions involving a motorcycle going straight and a four-wheel vehicle changing
lanes, roughly 90% of the time the human factors for the four-wheel vehicles suffering such collisions
involved a failure to confirm safety factors, and presumably there exist other cases that are similar tothe case example presented here.
In addition, the fact that Mr. A was speeding is a conceivable background reason that led to theaccident. As a result of speeding up to overtake the other vehicle, he presumably reached aconsiderable speed of over 100 km/h.
This resulted in a sizable difference in speed with Mr. B, who was traveling at roughly 85 km/h. As aresult, this conceivably led to the possibility that it was difficult for Mr. B to detect Mr. A, as well as thepossibility that it was difficult for Mr. A to sense Mr. B changing lanes, as he was located in Mr. A’s
side view.
However, there is also the conceivable possibility that had circumstances been slightly different, thiswould have resulted in a different type of accident. Had Mr. A been farther ahead or moving at ahigher rate of speed than he was in the accident case example, it could have conceivably resulted ina collision or contact accident caused by Mr. B against Mr. A.
Moreover, had Mr. A been farther behind or moving at a lower rate of speed than he was in theaccident case example, this would have opened up the conceivable possibility that he could haveinitiated evasive actions before getting into a rear-end collision. Yet had he tried to avoid an accident
by instantaneously applying the emergency brake, this could have potentially resulted in asingle-vehicle accident. For example, had his front wheel locked up it could have led to themotorcycle overturning, or had he lost control of the motorcycle this could have resulted in a collision
with the central median barrier or a guard fence.