ITARDA 25th Work Shop Report2022
25th Presentation Session for Traffic Accident Investigations, Analysis, and Research“Analysis of Situation Regarding Occurrences of Rear-End Collision Accidents
at Expressways and Effects of AEB”

Shinpei Yoshida
Researcher, Autonomous Driving Section, Autonomous Driving Group1

ITARDA 25th Work Shop Report

1. Introduction
1-1. Background and objectives of research
In recent years, in Japan, based on government strategies such as the “Public-Private ITS
Initiative/Roadmaps” and the “Advanced Safety Vehicle (ASV) Promotion Plan,” various initiatives
have been promoted with the aim of the early realization of autonomous driving. In order to realize asafe automotive society, it will be important to not only develop and popularize advanced safetyvehicles and autonomous vehicles that are equipped with driving support functions, but also to build
road traffic environments that support the operation of driving-support functions and autonomousdriving functions. In order to achieve this, it will be necessary to understand the types of road traffic
environments under which traffic accidents involving vehicles that have driving support functions are
occurring.
In the research on this occasion, we focused on autonomous emergency braking systems(hereinafter referred to as “AEB”) and targeted rear-end collision accidents that have occurred on
expressways. We compared the situations regarding accident occurrences among AEB-equipped
vehicles and non-AEB-equipped vehicles, and, based on this, we analyzed the accident reduction
effects of AEB according to traffic characteristics and lane-configuration differences.
1-2. Overview of autonomous emergency braking (AEB)
Using sensors such as in-vehicle cameras and millimeter-wave radar, AEB detects frontward
vehicle, pedestrians, and so on, and if there is a risk of a collision, it encourages the driver to operate
the brake via a warning, and if the system has determined that a collision is unavoidable, it controls
the brakes autonomously. Thus, AEB is a type of device that avoids collisions and mitigates damage
in the event of a collision. In Japan, in 2020, the percentage of new passenger vehicle equipped with
AEB(1) amounted to 91% (3,701,104 vehicles equipped with AEB among the total of 4,044,976
vehicles produced), and further popularization is anticipated in the future due to factors such as AEB
installation incrementally being made obligatory for new vehicles starting in November 2021.
2. Overview of analysis
2-1. Data used
In our analysis, we matched andTraffic accident
VehicleRoad traffic
AEB
information
⾞両情報
交通事故情報
ＡＥＢ情報
道路交通情報information
information
information
analyzed various types of data (traffic• Vehicle identification• Vehicle identification • Accident location• Traffic-survey basic
numbernumber(X, Y)
sections
・⾞体番号
・⾞体番号
・事故箇所
・交通調査基本••• Number・・（X,Y）
区間 of lanes
accident statistics, vehicle information,• Whether AEB• Registration number ・登録番号• Registration number ・⾞線数
• Daily traffic volume
・AEB搭載有無
・登録番号
equipped or nonroad traffic information, and AEB•・equipped
・
・事故類型
・⽇交通量
• Type of accident
•
•
・
・
・
•
•
information) that is in the possession of
the Institute for Traffic Accident Research
Matching
data for analysis
分析⽤マッチングデータ
and Data Analysis (hereinafter referred to
Figure 1. Image of creation of matching data for analysis
as “ITARDA”) (Figure 1). Whenmatching the data, we connected the vehicle identification number, which is included in AEB
information and vehicle information (automobile registration data), and the registration number,which is included in vehicle information and traffic accident information. Furthermore, based on
2

ITARDA 25th Work Shop Report

latitude and longitude information regarding accident locations that is included in the accident
information, we connected the accidents with the traffic-survey basic sections that are included in theroad traffic information (National Survey of Road and Street Traffic Conditions). As a result, we wereable to identify accidents caused by vehicles regarding which the status of AEB-equipment was clear,and the road traffic conditions at the locations of these accidents.
2-2. Analysis conditions and analysis methods
In our analysis, we targeted rear-end collision accidents that occurred on main roads such as
national expressways (excluding interchanges, junctions, and areas near toll booths) in which theprimary party was a passenger vehicle, as shown in Chart 1. In cases in which the vehicle was AEBequipped, and in cases in which the vehicle was non-AEB-equipped, we calculated the “numbers ofrear-end collision accidents per vehicle owned” as indicators showing accident-proneness, andcompared the differences. We calculated the specific indicators by dividing the sum of the numbersof rear-end collision accidents among AEB-equipped vehicles and non-AEB-equipped vehicles that
occurred during the targeted analysis period (2017 to 2020), by the sum of the numbers ofregistered/filed vehicles during the same time period (Chart 2). As a result, in regard to the “numbersof rear-end collision accidents per vehicle owned,” we do not take into consideration information
related to section distances and section traffic volumes, such as the “casualty accident rate (numberof accidents per traveler kilometer),” which is used for road performance assessments and so on. In
addition, since our analysis is focused on traffic characteristics and differences regarding road traffic
Chart 1. Analysis conditions
environments such as lane configurations, we do
Private ordinary passenger vehicle, private compact
Vehiclenot take into consideration factors such as thepassenger vehicle, private light four-wheel passenger(primary party)
vehiclegeneration and grade of AEB.
Division by road National expressways, national limited highways,
type
urban expressways, other limited highways
In the analysis, we carried out a chi-squared
Cruising lane (traffic lane 1, traffic lane 2 or above),
Road section
passing lane, climbing lane, acceleration/deceleration
test regarding whether there is a significant
lane & shoulder
correlation between whether vehicles are AEB- Type of accident Vehicle-to-vehicle rear-end collision accidents
Time period
2017 to 2020 (total of 4 years)
equipped or non-equipped, and the number of
AEB generation and grade, etc. are not taken into
Remarks
consideration.
rear-end collision accidents. If there is a
Chart 2. Numbers of registered/filed vehicles used in analysis
significance level of 1% (p < 0.01), this is shown
Time period
Non-AEB-equipped
AEB-equippedwith “**”, and if there is a significance level of2017 to 2020
41,179,081 vehicles
47,637,856 vehicles*The figures in this chart do not include vehicles of unknown AEB5% (p < 0.05), this is shown with “*”.
equipment status and some imported vehicles.
3. Analysis of situation regarding occurrence of rear-end collision accidents among AEBequipped and non-equipped vehicles based on differences in road type
With regard to each road type (“national expressways,” “national limited highways,” “urban
expressways,” and “other limited highways,”) we calculated the numbers of rear-end collision
accidents per vehicle owned among AEB-equipped and non-equipped vehicles, and the rate of3

ITARDA 25th Work Shop Report

Number of rear-end collision accidents per vehicle owned(cases/million vehicles)

保有台数あたり追突事故件数（件／百万台）reduction in rear-end collision accidents brought
60.0%
16.00
16.00
52.0%
13.84
13.84
14.00
14.00
12.83
12.83
50.0%
about by AEB-equipped vehicles (Figure 2).
12.00
12.00
**
40.0%
**
9.23
9.23
10.00
10.00
The result was that for both AEB-equipped
29.6%
29.6%
7.50
30.0%
7.50
8.00
30.0%
8.00
5.44
and non-equipped vehicles, the numbers of rear5.44
6.00
6.00
27.5%
4.43
20.0%
4.43 20.0%
7.3%
4.00
4.00
end collision accidents per vehicle owned were
10.0%
1.31
1.31
10.0%
0.92
2.00
2.00
0.92
0.0%
0.00
0.0%
0.00
highest regarding “national expressways,” with
National
Urban
Other
limited
高速自動車
一般国道
都市高速
その他
National
limitedexpressways highways
expressways
non-AEB-equipped at 13.84 cases/million
国道
自専道
自専道
highways
AEBNon-AEBRate of reduction
AEB非搭載AEB搭載
削減率
equipped
equipped
vehicles, and AEB-equipped at 12.83
Figure 2. Numbers of rear-end collision accidents per vehicle owned
among AEB-equipped and non-equipped vehicles, and rates ofcases/million vehicles. Meanwhile, for both
reduction in rear-end collision accidents brought about by AEBequipped vehicles (by road type)
AEB-equipped and non-equipped vehicles, thenumbers were lowest regarding “national limited highways,” with non-AEB-equipped at 1.31
cases/million vehicles and AEB-equipped at 0.92 cases/million vehicles. It seems that the differences
are largely due to the effects of road length and the amount of traffic volume. Furthermore, the rateof reduction in rear-end collision accidents brought about by AEB-equipped vehicles was lowest
regarding “national expressways,” at 7.3%, and there did not appear to be a significant difference
between AEB-equipped and non-equipped vehicles. Meanwhile, the rate was highest regarding “otherlimited highways,” at 52.0%, and there appeared to be a significant difference between AEB-equipped
and non-equipped vehicles. The rates regarding “national limited highways” and “urban expressways”
were similar, at around 30%, and in the results, a significant difference between AEB-equipped andnon-equipped vehicles could be seen regarding “urban expressways.”

保有台数あたり追突事故件数（件／百万台）Number of rear-end collision accidents per vehicle owned(cases/million vehicles)

4. Analysis of reduction effects of AEB-equipped vehicles on rear-end collision accidents withfocus on national expressways
4-1. Situations regarding occurrence of rear-end collision accidents divided by accident
content
16.00
16.00
8.0%
8.0%
7.6%
We calculated the numbers of rear-end
13.28
14.00
14.00
12.28
12.28
collision accidents per vehicle owned among
12.00
12.00
6.0%
6.0%
10.00
10.00
AEB-equipped and non-equipped vehicles, and
4.0%
8.00
8.00
4.0%
the rates of reduction in rear-end collision
2.3%
6.00
6.00
2.0%
4.00
4.00
2.0%
accidents brought about by AEB-equipped
2.00
2.00
0.56
0.55
0.56
0.55
vehicles at national expressways, divided by
0.0%
0.00
0.00
0.0%
Fatalities & serious injuries
Slight injuries
死亡・重傷
軽傷
accident content (Figure 3).
Non-AEBAEBRate of
AEB非搭載AEB搭載
削減率
equipped
equipped
reduction
In the results, “fatalities & serious injuries”
Figure 3. Numbers of rear-end collision accidents per vehicle owned
among AEB-equipped and non-equipped vehicles, and rates of
reduction in rear-end collision accidents brought about by AEBamounted to 0.56 cases/million vehicles
equipped vehicles (at national expressways, by accident content)
regarding non-AEB-equipped, and 0.55
cases/million vehicles regarding AEB-equipped, and thus the rate of reduction in rear-end collision
accidents brought about by AEB-equipped vehicles was 2.3%. Meanwhile, “slight injuries” amounted
to 13.28 cases/million vehicles regarding non-AEB-equipped and 12.28 cases/million vehicles
regarding AEB-equipped, and thus the rate of reduction in rear-end collision accidents brought about
by AEB-equipped vehicles was 7.6%. In both cases, there did not appear to be a significant difference
4ITARDA 25th Work Shop Report

between AEB-equipped and non-equipped vehicles.

Number of rear-end collision accidents per vehicle owned(cases/million vehicles)

保有台数あたり追突事故件数（件／百万台）

4-2. Reduction effects on rear-end collision accidents divided by speed limit
60.0%
We calculated the numbers of rear-end
60.0%
6.00
6.00
**
collision accidents per vehicle owned among
40.0%
40.0%
5.00
5.00
4.30
21.4%
33.7%
21.4%
4.30
4.14
4.14
3.97
3.97
AEB-equipped and non-equipped vehicles, and
17.7%
3.96
3.96
20.0%
20.0%
4.00
4.00
3.38
3.38
3.8%
the rates of reduction in rear-end collision
0.6%
0.0%
0.0%
3.00
3.00
2.62
-10.6%
2.62-17.5%
accidents brought about by AEB-equipped-20.0%-20.0%
2.00
2.00
vehicles at national expressways, divided by-44.1%-40.0%
0.51-40.0%
1.00
1.00 0.49 0.48
0.67
0.53 0.51
0.53
0.61 0.67
0.61
0.49 0.48
speed limit (Figure 4).
0.42
0.42 0.42
0.42
0.10
0.07
0.07 0.10-60.0%-60.0%
0.00
0.00
In the results, for both AEB-equipped andnon-equipped vehicles, rear-end collision
accidents frequently occurred at sections of “50km/h or below,” “80 km/h or below,” and “noRate of
Non-AEBAEBAEB非搭載
AEB搭載
削減率
reductionequipped
specified speed limit, etc.” Since our analysis
equipped
Figure 4. Numbers of rear-end collision accidents per vehicle owned
is limited to main-road sections, in the case ofamong AEB-equipped and non-equipped vehicles, and rates of reduction
in rear-end collision accidents brought about by AEB-equipped vehicles“50 km/h or below,” the rear-end collision(at national expressways, by speed limit)
accidents occurred when there was a temporary
Non-AEBrestriction on the speed limit. In such cases, for equipped
8%
63%
10% 5%
5% 14%14%63%
8%
AEB非搭載 10%
both AEB-equipped and non-equipped vehicles,
N=189
approximately 60% of the rear-end collision
AEB59%
15%
AEB搭載 6%
6% 5%
5% 15%
15%
59%
15%
accidents occurred when the speed limit was equipped
N=147
N=147
restricted due to traffic congestion (Figure 5).
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0% 10% 20% 30%
50%
70% 80% 90%
Meanwhile, “no specified speed limit, etc.”
Construction,
Abnormal
Other
Notapplicable
該当なし
異常気象
工事等
渋滞
その他
etc.
weatherrefers to sections where a speed limit is not set,
Figure 5. During rear-end collision accidents that occurred at national
expressways, causes of speed limit being temporarily set to 50 km/h or below
and thus it means sections with a legal speed
Chart 3. Requirements for AEB certification systems
limit of 100 km/h for the targeted analysis
Content
the vehicle is running at 50 km/h and approaching a frontward
vehicles (passenger vehicles). As such, in the Requirement Whenvehicle that is stopped, it must not collide with the other vehicle, orthe speed in the event of a collision must be reduced to at least 20(1)case of “80 km/h or below” and “no specified
km/h.
Requirement When the vehicle is running at 50 km/h and approaching a frontward
vehicle that is running at 20 km/h, it must not collide with the otherspeed limit, etc.,” the rear-end collision(2)
vehicle.
In Requirement (1) and Requirement (2), a warning must be given toRequirement
accidents are thought to have occurred at thethe driver encouraging collision avoidance operations at least 0.8(3)seconds before the AEB starts to operate.
general speed-limit sections of national
expressways.
Furthermore, looking at the rates of reduction in rear-end collision accidents brought about by
AEB-equipped vehicles, the highest level was 33.7% regarding “50 km/h or below”, and in the results,
there appeared to be a significant difference between AEB-equipped and non-equipped vehicles. At
sections with other speed limits, although there did not appear to be a significant difference between
AEB-equipped and non-equipped vehicles, a trend could be seen in which the rate of reduction
decreased as the speed limit increased. According to the requirements of the AEB certification systemset forth by the Ministry of Land, Infrastructure, Transport and Tourism as shown in Chart 3, there
Trafficcongestion.

5

ITARDA 25th Work Shop Report

are no requirements regarding cases in which the vehicle is approaching another vehicle at more than
50 km/h. Taking this point into consideration, it seems that in the case of running at more than 50
km/h, there are many difficult situations in which the operable range of the AEB is exceeded, or acollision cannot be avoided even if the AEB is able to operate.
Furthermore, as shown in Figure 2 mentioned above, there was a result in which, at national
expressways, the rate of reduction in rear-end collision accidents brought about by AEB-equipped
vehicles was lower compared with other road types. As for the reason for this, it seems that one factor
may be the fact that since national expressways have the highest designated speed limit, the speedsof cruising vehicles may be high compared with other types of roads.
5. Analysis of reduction effects of AEB-equipped vehicles on rear-end collision accidents
according to lane-configuration differences
We calculated the numbers of rear-end collision accidents per vehicle owned among AEB-equipped
and non-equipped vehicles, and the rates of reduction in rear-end collision accidents brought about
by AEB-equipped vehicles, divided by lane configuration, regarding the two different road types“national expressways” and “urban expressways” (Figure 6, Figure 7).
For example, focusing on the numbers of rear-end collision accidents per vehicle owned regarding“4-lane,” in the results, at both types of roads, the numbers were lower regarding “traffic lane 1” than“passing lane” for both AEB-equipped and non-equipped vehicles. Furthermore, looking at the rates
of reduction in rear-end collision accidents brought about by AEB-equipped vehicles regarding “4lane,” in the results, at national expressways, the rate was lower regarding “passing lane” (5.0%),
than it was regarding “traffic lane 1” (27.5%). Meanwhile, at urban expressways, the rate was 27.6%
regarding “traffic lane 1” and 27.2% regarding “passing lane,” and thus there did not appear to be anotable difference concerning the driving lane.
At 4-lane-or-above national expressways, vehicle groups running in traffic lane 1 have a cruising
speed that is relatively low. As such, compared with the passing lane, the number of occurrences ofrear-end collision accidents is low, and this seems to explain the trend of a higher rate of reduction inrear-end collision accidents brought about by AEB-equipped vehicles. Meanwhile, at 4-lane urban
expressways, there is a trend in which vehicle groups have a low cruising speed due to the designated

6-laneor above
6車線以上

Passinglane

Traffic lane 2 orabove

Traffic lane 1

Traffic lane 1

Traffic lane 1

Number of rear-end collision accidents per vehicle owned(cases/million vehicles)

Passinglane

Traffic lane 2 orabove

Traffic lane 1

Passing lane(including
traffic lane 2)

Traffic lane 1

Traffic lane 1

Passing lane(including
traffic lane 2)

4-lane4車線

追越車 線

2-lane2車線

第二通行帯以上)

AEB-equipped

第一通行帯

追越車線
第(二通行帯含

第一通行帯

AEB非搭載AEB搭載
Rate of reduction
削減率

Non-AEB-equipped

6.00
6.00
90.0%
90.0%
**
42.4%
42.4%
32.8%
32.8%
5.00
5.00
60.0%
60.0%
27.6%
27.6% 4.32
27.2%
28.0%
28.0%
4.32 27.2%
4.00
4.00
30.0%
30.0%
3.15
*
3.00
3.00
0.0%
0.0%
2.09
1.51
2.00
2.00
-30.0%
1.51-8.1%-8.1% -30.0%
0.44 0.31
1.00 0.07
0.44
1.00-60.0%
0.22
0.22 0.15
0.07 0.04
0.15
0.10 0.10 -60.0%
0.00
0.00
-90.0%-90.0%
第一通行帯

6-laneor above
6車線以上

追 越車 線

4-lane4車線

第二通行帯以上)

2-lane2車線

第一通行帯

追 越車 線
第(二通行帯含

第一通行帯

第一通行帯

Number of rear-end collision accidents per vehicle owned(cases/million vehicles)

保有台数あたり追突事故件数（件／百万台）

保有台数あたり追突事故件数（件／百万台）

*
90.0%
6.00
90.0%
6.00
5.12 4.87 46.0%
5.12
46.0%
60.0%
5.00
27.5%
27.5%
60.0%
5.00
13.6%
13.6%
**
30.0%
4.00
30.0%
4.00
3.16
3.16
0.0%
3.00
3.00
2.29 0.0%
2.04 1.76
1.76* 2.04
2.29
7.4%
7.4%
1.36
1.36
5.0%
5.0%
-30.0%
2.00-30.0%
2.00
0.97
0.68
0.68 0.63
0.63
0.52
0.52
-60.0%
1.00
1.00-60.0%
68.3%-68.3%-90.0%
0.00
0.00-90.0%

AEB非搭載AEB搭載
Rate of reduction
削減率
Non-AEB-equipped
AEB-equipped*5-lane is included in 4 -lane, and 3-lane is included in 2-lane.

*5-lane is included in 4 -lane, and 3-lane is included in 2-lane.

Figure 6. Numbers of rear-end collision accidents per vehicle owned
among AEB-equipped and non-equipped vehicles, and rates of
reduction in rear-end collision accidents brought about by AEBequipped vehicles (by lane configuration at national expressways)

Figure 7. Numbers of rear-end collision accidents per vehicle owned
among AEB-equipped and non-equipped vehicles, and rates of
reduction in rear-end collision accidents brought about by AEBequipped vehicles (by lane configuration at urban expressways)

6

ITARDA 25th Work Shop Report

speed limit being low, and due to the structure of such roads, there are entrances and exits on the rightside, and distances for merging are short. Thus, it is envisioned that there are no significant differencesin the speeds of vehicle groups running in the traffic lane 1 and the passing lane, and this seems to
explain the result in which the rates of reduction in rear-end collision accidents were similar.
6. Conclusion
For the research on this occasion, we carried out matching regarding various types of data in thepossession of ITARDA (traffic accident statistics, vehicle information, road traffic information, and
AEB information), and this enabled us to identify accidents caused by AEB-equipped and nonequipped vehicles, and the road traffic conditions at the locations of the accidents. Furthermore, wetargeted rear-end collision accidents that occurred at expressways, and compared the situations
regarding accident occurrences among AEB-equipped vehicles and non-AEB-equipped vehicles(numbers of accidents per vehicle owned). In the results, we were able to quantitatively show the
reduction effects of AEB-equipped vehicles on rear-end collision accidents according to road typeand lane-configuration differences.
We are considering carrying out analysis in the future that targets low-speed general roads(regarding which AEB is expected to be highly effective for accident avoidance and damage
mitigation), and additionally makes use of property-damage information. Furthermore, looking aheadto the popularization of autonomous vehicles, it seems that it will be important to carry out analysis
regarding road traffic environments with a focus on driving support functions such as adaptive cruise
control. Nevertheless, since such analysis would require taking into consideration whether suchfunctions are turned on or off, it seems that examining new analysis and evaluation methods will bea challenge.
<Acknowledgments>
This research was implemented with support from the Intelligent Transport System (ITS)
Promotion Office, Road Traffic Control Division, Road Bureau, Ministry of Land, Infrastructure,
Transport and Tourism. We would like express our appreciation here.
<Citations and references>(1) Ministry of Land, Infrastructure, Transport and Tourism: Comprehensive Automotive Safety
Information, Survey on the Status of the Popularization of ASV Technologies,
https://www.mlit.go.jp/jidosha/anzen/01asv/data/r3souchakudaisu.pdf(2) Ministry of Land, Infrastructure, Transport and Tourism: Overview of Autonomous Emergency
Braking Certification System, https://www.mlit.go.jp/jidosha/AEBS.html(END)7