ITARDA

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

88

No.
0

2011
APRIL

2

Fatality rate (%)

4

6

Head-on collision
0.70%

Rear-end collision (while moving) 4.7%
Rear-end collision (others)
0.70%

Crossing collision

8

0.47%

Collision while passing/overtaking
0.63%

Collision while passing each other
0.22%

Collision while turning left
0.29%

Collision while turning right (going straight)
0.30%

Fatality rate inrear-end collisions is

10

times

higher than incrossing collisions

Collision while turning right (others)
0.28%

Vehicle-to-vehicle (others)
0.47%

Vehicle-to-vehicle (total)
0.47%

Fatality rate for bicyclists bytype of accident

Special feature

Rear-end collisions with a moving
bicycle—posing a high risk of death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

2011 APRIL

88

No.

Special feature

Rear-end collisions witha moving bicycle—posing
a high risk of death
According to statistics, when a bicycle is involvedin a traffic accident, it is typically hit by a car at anintersection (crossing collision). However, a rearend collision, i.e., one in which a moving bicycle
is hit from behind by a car, is much more lifethreatening than any other type of accident,
despite its low incidence rate. (Throughout thisanalysis, “rear-end collision” refers to crashing intoa bicycle that is traveling and does not include
bicycles that are stationary.)
While bicycle riders are often found to be
responsible for collisions with a car in general,
rear-end collisions are mostly attributable to car
drivers. In many cases, this type of accident canbe prevented by always trying to predict andavoid possible dangers while driving. In this issueof ITARDA Information, we explore effective ways
to drive in order to achieve this objective.

CONTENTS

1 Overview of bicyclists in rear-end collisions
2 Characteristics of rear-end collisions
3 Factors for looking away from the road or
becoming inattentive while driving

4 Examples of accidents
5 Conclusion
2

ITARDA INFORMATION 88

走行中自転車への追突事故

特集

Overview of bicyclists inrear-end collisions

CTION
SE

1

(1) Fatality rate and number of bicyclists involved
For all bicycle riders involved in traffic accidents,
both as the primary party (“Party 1”) and thesecondary party (“Party 2”)*, the fatality rate and thenumber of casualties are shown in Fig. 1 by accident
type and degree of injury. The traffic accident data
used in this analysis is the total number of casualties
recorded between 2001 and 2009.
Number ofdeathsFatality rate =Number ofcasualties

×100(%)

The category “Crossing collision” presents the highest
number of deaths and casualties, but focusing on the

fatality rate, there is a remarkably high rate of 4.7%, or
1 in 20, for rear-end collisions. The rate for “Crossing
collision” is only 0.47%, or 1 in 200, meaning that the riskof death is 10 times higher when a bicycle is struck frombehind.
According to Fig. 2 illustrating whether the bicycle wasParty 1 or Party 2 in each type of accident, bicycles aremost likely to be Party 2 in rear-end collisions, comparedto the case of crossing collisions in which a certain
percentage is Party 1.
*Of the two parties directly involved in a traffic accident, the more negligent one
is designated as the primary party and the other one the secondary party. If thelevel of negligence is almost the same, the less injured party is regarded as theprimary party.

6
4.7%■ Fatality rate

4

Fatality
rate
(%)

2
0.70%

0

Head-oncollision

0.70%
Rear-end
collision(while moving)

0.70
264
3,666
33,81937,749Fatality rate
Fatalities
Serious injuries
Minor injuries
Casualties

4.7
611
2,156
10,186
12,953Rear-end
collision(others)

0.70
53
553
6,968
7,574

0.63%

0.47%

Crossing
collision

0.22%

0.29%

0.30%

0.28%

Collision while Collision while
Collision
Collision while
Collision whileturning rightwhile passing/ passing eachturning rightturning left
(going straight)
overtaking(others)
other

0.47
3,877
60,428763,666
827,971

0.63
236
3,915
33,35337,504

0.22
63
1,822
26,76528,650

0.29
473
7,669
154,295
162,437

0.30
219
5,200
68,16673,585

0.28
297
7,070
99,404
106,771

0.47%

0.47%

Vehicleto-vehicle(others)

Vehicle-tovehicle (total)

0.47
957
13,735
186,935
201,6270.47
7,050
106,214
1,383,557
1,496,821

Fig. 1: Fatality rate for bicyclists by type of accident (vehicle-to-vehicle accidents)(*Bicyclists as primary or secondary party)■ Party 1■ Party 2

100
80
Percentage
(%)

60
40
20
0

Parties 1+2

Fatalities

Party 1
Party 2
Parties 1+2

Casualties

Party 1
Party 2

Head-oncollision

Rear-end
collision(while moving)

264
56
208
37,7495,500
32,249611
4607
12,953430
12,523Rear-end
collision(others)

53
5
48
7,574
1,279
6,295

Crossing
collision

3877
1,466
2,411
827,971
106,072
721,899

Collision while Collision while
Collision
Collision while
Collision whileturning rightwhile passing/ passing eachturning rightturning left
(going straight)
overtaking(others)
other

236
22
214
37,504
2,246
35,25863
18
45
28,6502,450
26,200473
6
467
162,437
1,925
160,512219
24
195
73,585
1,842
71,743297
32
265
106,771
3,653
103,118

Vehicleto-vehicle(others)

Vehicle-tovehicle (total)

957
7,050
200
1,833
757
5,217
201,627 1,496,821
17,116
142,513
184,511 1,354,308

Fig. 2: Number of fatalities for bicyclists as primary or secondary party by accident type(vehicle-to-vehicle accidents)
88 ITARDA INFORMATION

3

特集

走行中自転車への追突事故(2) Breakdown of Party 1 in rear-end collisions
The primary party hitting a bicycle from behind ingeneral includes motorcycles and bicycles (Fig. 3).
However, regarding only fatal accidents, the blameis almost always placed on the four-wheeled vehicle(hereafter “car”). Therefore, we deal exclusively withcar (as Party 1)-to-bicycle (as Party 2) accidents inthis analysis. Also, since bicycle riders are almost
always the most severely injured party in this typeof accident, we focus on the number of accidents
rather than casualties.

Casualties for bicyclists as Party 2 (n = 11,372)

Fatalities for bicyclists as Party 2 (n = 601)

Bicycles 0%

Others 0%

Bicycles3%

Others 1%

Motorcycles 2%

Motorcycles
18%

Four-wheeled vehicles

Four-wheeled vehicles

79%

98%

Fig. 3: Vehicle type of primary party in rear-end collisions (while moving)(*Excluding hit-and-run accidents where the primary party is unknown)(3) Traffic violations on the part of bicyclists
Figure 4 shows how many bicycle riders as Party
2 did not commit a traffic offense, along with the“non-violation rates”.
Non-violation=
rate

Number of nonviolative cases
Number of total
accidents

×100(%)In rear-end collisions, the rate goes up to 82% incomparison to 29% in the case of crossing collisions.
In other words, 82% of the car drivers were
responsible for the rear-end collisions, which meansthat this type of accident can usually be prevented
by always trying to predict and avoid possible
dangers while driving.

100
82%

80
Non-violation
rate (%)

75%■ Non-violation rate

60
40

49%
31%

40%

49%

43%

51%

44%

29%

38%

20
0
Non-violation rate (%)
Non-violative cases
Total accidents

Head-oncollision

31
5,980
19,099Rear-end
collision(while moving)

82
7,450
9,054

Rear-end
collision(others)

75
3,639
4,823

Crossing
collision

29
187,536
640,686

Collision
Collision while
Collision
Collision
Collision
while passing/ while passing while turning
turning rightwhile turning
overtaking(going straight) right (others)
each otherleft

49
12,472
25,21940
7,339
18,47549
74,599150,71043
28,83566,75951
49,59996,951

Fig. 4: Non-violation rate for bicyclists by accident type(*Primary party = car, secondary party = bicycle)

4

ITARDA INFORMATION 88

Vehicleto-vehicle(others)

Vehicle-tovehicle (total)

44
38
70,168447,617161,050 1,192,826

CTIONSE

2

Characteristics
of rear-end collisions

To understand the characteristics of rear-end
collisions, we regard all types of collisions involving
cars (Party 1) and bicycles (Party 2) as “ Total
accidents” for easy comparison in this section. The
figures include all accidents causing fatalities andinjuries unless otherwise stated, since the numberof fatal accidents alone is too low to obtain a clear
general trend.

While more than half the “Total accidents” comprise“Stopped or under 10 km/h”, higher speed ranges
such as “Over 40 km/h” (29%) are dominant in rearend collisions instead of the lowest speed range,
which is the least frequent in this type of accident. It
can be concluded that cars tend to be traveling fastat the time of a rear-end collision.

(1) Speed immediately before accident
The graph below (Fig. 5) shows the vehicle speed
immediately before the crash, taken from our traffic
accident database and originally categorized as
the danger recognition speed (i.e., the speed when
the driver recognized the danger of an accident).

(2) Type of road
The type of road most likely to induce a collision (Fig.
6) is the intersection in the case of “Total accidents”(72%), whereas a large proportion of rear-end
collisions happened on stretches of road where
there is no intersection (78%).

3%

Total accidents
n = 1,190,000

52%

Rear-end collision(while moving)n = 9,054

7%

15%

27%

21%

0

20

12%

28%

40

■ Stopped or under 10km/h■ Up to 20 km/h
■ Up to 30 km/h
■ Up to 40 km/h
■ Over 40 km/h
■ Unknown

6%

29%

60

80

100

Percentage

Fig. 5: Car speed immediately before crash1%

Total accidents
n = 1,190,000

72%

Rear-end collision(while moving)n = 9,054

11%

4%

10%

23%
■ Intersection■ Near intersection■ Non-intersection
location■ Others

78%
1%

0

20

40

60

80

100

Percentage

Fig. 6: Type of road at accident site

88 ITARDA INFORMATION

5

特集

走行中自転車への追突事故(3) Time of day
Nighttime accidents account for nearly half therear-end collisions, compared to a low incidence
rate for “Total accidents” (Fig. 7). When restricted toTotal accidents
n = 1,190,000

fatal accidents, the incidence rate of 39% for “Total
accidents” jumps to 72% for “Rear-end collisions”(Fig. 8).

78%

Rear-end collision(while moving)n = 9,054

22%

53%

0

20

47%

40

60
Percentage

80■ Daytime■ Nighttime

100

Fig. 7: Time of accident involving fatalities and injuries by time of day

Total accidents
n = 5,031

61%

Rear-end collision(while moving)n = 591

39%

28%

0

72%

20

40

60
Percentage■ Daytime■ Nighttime

80

Fig. 8: Time of accident involving fatalities by time of day

6

ITARDA INFORMATION 88100

(4) Human factors on the part of car drivers
With respect to the causes of accidents classified inFig. 9 in terms of human factors on the part of the
car driver (Party 1), a delay in noticing the bicycle
ahead is the major cause for both rear-end and alltypes of collisions.

The main cause of the delay is failure to check safety
for “Total accidents”, but in rear-end collisions drivers
typically overlooked the bicycle ahead by looking
elsewhere or being inattentive, adding up to 82%(Fig. 10). Drivers tend to be less attentive at night
than during the day according to Fig. 11, suggestingthat bicycles are more easily overlooked in the dark.

1%

Total accidents
n = 1,190,00087%

Rear-end collision(while moving)n = 9,054

12%

78%

■ Delay in noticing■ Error in judgment■ Error in operation■ Unknown

19%
2%

0

20

40

60

80

100

Percentage

Fig. 9: Human factors in accidents for car drivers

3%

Total accidents
n = 1,040,000

6%Rear-end collision(while moving)n = 7,098■ Became inattentive(internal factor)■ Took his/hereyes off the road(external factor)■ Failed to confirm
safety

91%

27%

0

55%

20

40

18%

60

80

100

Percentage

Fig. 10: Breakdown of the factor “Delay in noticing”

Daytimen = 3,399

22%

Nighttimen = 3,699

57%

32%

0

53%

20

40

■ Became inattentive(internal factor)■ Took his/hereyes off the road(external factor)■ Failed to confirm
safety21%

60
Percentage

15%

80

100

Fig. 11: Breakdown of the factor “Delay in noticing” in rear-end collisions by time of day
88 ITARDA INFORMATION

7

特集

走行中自転車への追突事故(5) Traffic violations committed by bicyclists
Looking at the causative factors on the part ofthe bicycle riders (Fig. 12), apart from the largest
category “No violations”, 6% is “Failure to confirm
safety behind them” when changing lanes, turning

Failure to confirm
safety behind them 6%
Incorrect manner ofriding 2%
Incorrect use of
roadway 2%

right or left, or crossing the road. Other offenses
include “Incorrect use of roadway” (not traveling on
the far left side of the road, two bicycles travelingside by side, etc.) and “Incorrect manner of riding”,
constituting 2% each.

Unknown 1%
Others7%

No violations
82%

n = 9054 cases

Fig. 12: Details of violations by bicyclists
To sum up, rear-end collisions while the bicycle ismoving exhibit the following characteristics:❶ The speed of the car immediately before thecrash is usually over 40 km/h (in the medium- tohigh-speed range),❷ These accidents occur more often on stretchesof road where there is no intersection and atnighttime,❸ The major human factor on the part of the
car driver is the delay in noticing the bicycle(about 80%), more than 80% of which is due to“Took his/her eyes off the road” and/or “Became
inattentive”, particularly at nighttime,8

ITARDA INFORMATION 88❹ Bicycle riders sometimes fail to fully checkthe traffic behind them when changing lanes,
turning right or left, or crossing the road.
Based on the above human factors and the daytime/nighttime data, rear-end collisions are more likely
to happen at night presumably because the car
driver is less attentive and the shape of the bicycle
is difficult to see from behind.

CTIONSE

3

Factors for looking away from the roador becoming inattentive while driving

We don’t know from the above data why car drivers
look away from the road or become inattentive
while driving. This section explores the factors
leading to these conditions based on ITARDA’s indepth study database.
From all the traffic accidents involving cars andbicycles covered by our database, 31 cases can beextracted as rear-end collisions, many of which
occurred at nighttime (Table 1). As to whether or
not the car drivers had noticed the bicycle, 24 ofthem did not see the bicycle until it was too late,mostly at nighttime, whereas 7 drivers noticed thebicycle in advance, especially in the daytime.
(1) Factors for the delay in noticing the bicycle
The direct factors for the delay in the 24 cases
above can be roughly classified into “visibility”,“conspicuity”, and “traffic conditions”:❶ Visibility: Of the 22 nighttime accidents, 18 cases
occurred on roads with no streetlamps. Other
factors affecting the delay were driving withlow beams despite no oncoming cars (3 cases)
and driving with reduced visibility due to rain (3cases).
❷ Conspicuity: Of the 11 cases in which the colorof the bicyclist’s clothes was known, 9 were
wearing dark-colored clothes. There was alsoa case in which the driver noticed a bicycle on
the far side of the road in advance, but only
recognized the presence of another bicycle
traveling alongside near the middle of the roadjust before the crash.

❸ Traffic conditions: In 5 cases, the driver was
distracted by oncoming cars on roads of 4.7 to 5.6
meters wide. Other traffic conditions affecting
the delay were little/no traffic (4 cases) and theprovision of a wide sidewalk that the driverthought the bicycle would use (1 case).
(2) Background of delay in noticing the bicycle
It is believed that these drivers were inattentive
because they should have been able to see thebicycle from a sufficient distance to avoid a collision
if they had been paying attention. The underlying
premise was “there must be no bicycles here” on the
grounds that:❶ It’s the middle of the night and raining hard,❷ There are usually no bicycles here at this time ofday (night),❸ There is hardly any traffic now so I can look awayfrom the road for a little while (daytime),❹ I’m sure all the bicycles are riding on the widesidewalk here (daytime).
These are the only four clearly stated commentsfrom interviews that we conducted with the drivers
involved in the above accidents. Although several
factors may directly cause a delay in noticing thebicycle, the assumption that “there must be no
bicycles here” may be the biggest contributory
factor to drivers losing their concentration. This
assumption is more prevalent at nighttime.

88 ITARDA INFORMATION

9

特集

走行中自転車への追突事故(3) Causes of accidents even after noticing thebicycle in advanceThe following are the causes of 7 accidents in which
the car driver noticed the bicycle in advance:❶ The driver looked away from the road after
catching sight of the bicycle (4 cases),❷ The bicycle changed lanes without looking back(1 case),❸ The bicycle crossed the road diagonally from theright at an intersection (1 case),❹ The driver took a certain action to avoid danger(1 case).
In many cases, the driver did not keep his/her eyeson the road even after noticing the bicycle.

DaytimeNighttime

Total

Delay in noticing

2

22

24

Noticed

5

2

7

Total

7

24

31

Table 1: Number of accidents by early/late notice and time of day for car drivers(*Primary party = car, secondary party = bicycle)

FactorVisibility

Conspicuity

Trafficconditions

DaytimeTotal

Dark road18

Low beams

3

Rain

3

Dark clothes

9

Traveling side by side1

Distracted by oncoming cars

5

Little/no traffic

4

Provision of wide sidewalk

1

Table 2: Number of accidents by factor in “Delay in noticing” for car drivers(multiple answers)

10

ITARDA INFORMATION 88

CTIONSE

4

Examples of accidents

Below is a detailed description of one accident casefrom our database analyzed in the previous section.
Situation
A man in his 40s was driving a standard-sized cargovan (A) on a dark two-lane road with no streetlamps
shortly after 11 pm in a heavy rain. There were no
oncoming cars ahead, but he used low beam to
avoid having to switch high/low beams according
to the traffic in the opposite lane. While drivingon a familiar road at about 45 km/h as usual,absentmindedly looking ahead in a relaxed moodafter work, he suddenly heard a crash and realizedthat the left front corner of his car had struck abicycle (B) from behind. He said that he did not
notice the bicycle because he never thought that abicycle or pedestrian would be on the road in suchheavy rain in the middle of the night.
The bicycle rider sustained serious injuries in thecrash.

A1
B1

B2

Diagram of the crash

B: Bicycle

B

A

Accident site
Bicycle B traveling on the left-hand side of the road wasstruck by Car A.

A

Accident site seen from 30 m away
There were, presumably, no objects blocking the ﬁeldof vision at the time of accident and therefore the driverwould have noticed Bicycle B if he had considered that
there might be a bicycle on the road.

88 ITARDA INFORMATION

11

CTIONSE

5

Conclusion(2) Findings from our database
The analysis of our in-depth study database
identified several different factors directly causing
the delay in noticing the bicycle ahead:❶ Visibility:Dark roads, low beams, rain
❷ Conspicuity:Bicyclist wearing dark clothes,
two bicycles traveling side by side
❸ Traffic conditions:Distracted by oncoming
cars, little/no traffic, assumption that bicycles
would ride on the sidewalk
It is considered that the drivers were inattentive
largely due to their incorrect assumption that“there must be no bicycles here”.
In many cases, the driver did not keep his/hereyes on the road even after noticing the bicycle.

❶ For car drivers
a To notice the bicycle as soon as possible,
Assume that bicycles are everywhere at any time,
Assume that bicycles are basically on the roadway,
not the sidewalk, as prescribed in the law,
When turning your attention to oncoming carsin the opposite lane, continue to pay attention to
the bicycle in your lane,
Try switching to high beams whenever there are
no oncoming cars.
b After noticing the bicycle,
Reduce the vehicle speed to maintain a safe
distance from the bicycle ahead, paying close
attention until you have passed it.
❷ For bicycle ridersa To protect yourself,
Wear bright-colored clothes, reflectors atnighttime, etc., to be more visible to car drivers,
Be sure to check the traffic behind you beforechanging lanes.
In analyzing the traffic accidents, both car drivers
and bicycle riders exhibited dangerous behavior
that resulted in an accident. However, even insimilar situations, most drivers and bicyclists
avoid an accident by taking preventive action. It isessential for both parties to obey traffic rules andproper driving manners and to slow down to a safe
speed.
Since bicycle riders are usually not held responsible
in rear-end crashes, car drivers are strongly urged
to always try to predict and avoid possible dangers
while driving, to reduce the number of fatalities
and the number of accidents itself.

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（財）
日本自動車研究所内
TEL029-855-9021 FAX029-855-9131

2011
APRIL

88

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❶ The speed of the car immediately before thecrash is usually over 40 km/h (in the mediumto high-speed range),❷ These accidents occur more often on stretchesof road where there is no intersection and atnighttime,❸ The major human factor on the part of the
car driver is the delay in noticing the bicycle(about 80%), more than 80% of which isdue to “Took his/her eyes off the road” and/or “Became inattentive”, par ticularly atnighttime,❹ Bicycle riders sometimes fail to fully checkthe traffic behind them when changing lanes,
turning right or left, or crossing the road.

(3) Precautions against rear-end collisions
The precautions from the above analysis are as
follows:

イタルダ・インフォメーション(1) Characteristics of rear-end collisions
The analysis of the accident data revealed thefollowing characteristics of rear-end collisions, themost fatal among all types of collisions involving
cars and bicycles:

Institute for Traffic Accident Research and Data Analysis

走行中自転車への追突事故

ITARDA INFORMATION

特集

23
4

-

-

5

S