ITARDA 23th Work Shop Report

2020
23rd Presentation Session for Traffic Accident Investigations, Analysis, and Research

Analysis of Compatibility Issues in Frontal Collision Accidents Between Vehicles

Masanori Taniguchi
Senior Researcher, Research Division

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ITARDA 23th Work Shop Report

1.

Introduction
Discussions have started on whether MPDB *1 frontal collision tests (Fig. 1)—which evaluate compatibility

in frontal collisions between vehicles of different weights or sizes and were adopted for vehicle assessments in
Europe from January of 2020—should be adopted domestically in Japan. Because vehicle types and roadenvironments differ between Europe and Japan, it is necessary to discuss the possibility of adoption anddetermine conditions by first considering the types of accidents that occur in Japan.
In research performed jointly with the Japan Automobile
TestvehicleManufacturers Association (JAMA) in 2018 and 2019, roadtraffic accident integrated data (hereinafter, “macro data”)
and accident investigation data (hereinafter, “micro data”)
were used to analyze frontal collisions of vehicles withdifferent weights and sizes in order to assess characteristics and50% overlap
Moving Deformable Barrier(with honeycomb) 1400kg

Fig. 1 - Compatibility evaluation tests inEuropetrends.
*1) Mobile Progressive Deformable Barrier

2.

Analysis subjects
There are two types of frontal collisions between vehicles—those that take place between vehicles of thesame weight and size, and those between vehicles with different weights and/or sizes. Although accidents
between vehicles of the same weight and size are covered by fixed-wall collision tests performed by JNCAP *2,evaluation methods for accidents between vehicles with different weights and/or sizes have yet to take shape inJapan. The goal of compatibility is to ensure the protection performance of the driver’s own vehicle, while
simultaneously reducing any damage caused to the opposing vehicle. For this reason, it is important to suppress
the aggressiveness (harmfulness) of heavy and large vehicles, while improving protection levels provided tolight and small vehicles. Because compatibility is determined by factors such as vehicle weight difference,
speed difference, collision energy distribution, force interaction at the front of the vehicle, vehicle bodystrength, and passenger tolerances, variables from macro data such as vehicle weight, speed, passenger
attributes, as well as variables from micro data such as injuries/points of contact, bumper height, and dashboard
intrusion amounts, were extracted and subjected to analysis *3. Conditions for data extraction are as shown inTable 1.
Table 1. - Main data extraction conditions
Macro &Microdata

Type of accident/Area of collision
Parties concerned and injuries
Vehicle types and applications
Vehicle weight

Macrodata
Microdata

Year of accident (year of survey)
Year first registeredYear of accident (year of survey)
Year first registered

Vehicle-to-vehicle frontal collision/Vehicle front
Death/serious injury/slight injury of primary and secondary
drivers (wearing seat belts)
Kei, small, and medium-sized (passenger) vehicles
Unladen vehicle weight (topped-off fluids, excluding tools andspare tires)2008-2017
Two groups: 2001-2007 / 2008-2017
2005-20172005-2017*2) Japan New Car Assessment Program*3) This document shows excerpts of analysis results mainly from the results of joint research and from the viewpoint of vehicle weight.

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ITARDA 23th Work Shop Report3.

Analysis using macro data

3-1.

Changes in distribution for the number of fatally or seriously injured drivers
Figure 2 shows the distribution of composition rates for the number of fatally or seriously injured drivers

in their own vehicles during vehicle-to-vehicle frontal collision accidents. In this figure, both the horizontal
axis (driver’s own vehicle) and vertical axis (opposing vehicle) plot vehicle weights in 100 kg increments (e.g.,
600~: from 600 kg to less than 700 kg). The plot size indicates the ratio size. Also, the figure has been split into
four quadrants for the sake of convenience, with the Quadrant I showing driver vehicles between 600 to lessthan 1,300 kg and opposing vehicles between 600 to less than 1,300 kg, Quadrant II showing driver vehicles
between 600 to less than 1,300 kg and opposing vehicles of 1,300 kg or more, Quadrant III showing drivervehicles of 1,300 kg or more and opposing vehicles between 600 to less than 1,300 kg, and Quadrant IVshowing driver vehicle of 1,300 kg or more and opposing vehicles of 1,300 kg or more. 600 kg is roughly thelower limit for passenger cars in the Japanese domestic market, while 1,300 kg is the midpoint of the 600 and
2,000 kg range that makes up the large majority of vehicles in the Japanese domestic market. From Figure 2, it
can be seen that the ratio of registered driver vehicles weighing from 600 to less than 1,300 kg increased from
83.3% in 2001-2007 to 87.0% in 2008-2017. In other words, the distribution for the number of fatally orseriously injured persons shifted to Quadrants I and II, which are made up of driver vehicles lighter than 1,300kg.
When separating individuals into the age groups of “65 and older” and “younger than 65” (Fig. 3), it canbe seen that the rate for the number of fatally or seriously injured persons made up of individuals aged 65 orolder in vehicles registered between 2008 and 2017 increased from 19.3% to 25.5%, while the rate forindividuals younger than 65 decreased. This means that the distribution for the number of fatally or seriously
injured drivers in vehicles registered between 2008 and 2017, particularly the number of fatally or seriously
elderly

drivers,

shifted

toQuadrants I and II, which have lighter
Opposing vehicle weight

Quadrant II 27.2→28.7%

vehicle weights than vehicles registeredin 2001 to 2007. Accordingly, in order toreduce numbers of fatally or seriously
injuredpersons

invehicle-to-vehicle

frontal collision accidents, efforts that

7.9→5.7% Quadrant IV(kginjuredIncrease
Decrease
Vehicles registered
between 2001 and 2007

Vehicles registered
between 2008 and 2017*: Significance level p < 0.05

focus on protecting lightweight vehicles

Quadrant I 56.1→58.3%

8.8→7.3% Quadrant III

and elderly drivers are needed.
Driver vehicle weight (kg)

Number of fatally or
seriously injured persons
in macro data
2001-2007: n = 1,051
2008-2017: n = 616

Values inside the plot are the composition rate (%) of vehicles(survey years 2008-2017)

registered between 2008 and 2017
Composition rates:
Numbers after the decimal point are hidden
Composition rate subtotals:
Numbers after the second number following the decimal point
are rounded up

Fig. 2 - Composition rates for numbers of fatally or seriously injured drivers during vehicle-to-vehicle
frontal collision accidents365 or oldervehicles registered between 2008 and 2017
Composition rates:
Numbers after the decimal point are hidden
Composition rate subtotals:

Opposing vehicle
weight (kg)Values inside the plot are the composition rate (%) ofYounger than 65

Number of fatally or seriously injured persons
in macro data
[2001 to 2007] 65 or older: n = 224, Younger
than 65: n = 827[2008 to 2017] 65 or older: n = 175, Younger
than 65: n = 441

Opposing vehicle
weight (kg)

ITARDA 23th Work Shop Report

Quadrant II 5.4→8.3%

1.0→1.8% Quadrant IVIncrease
Decrease
Quadrant I 13.9→17.2%

1.0→1.1% Quadrant III

Quadrant II 21.8→20.5%

6.9→3.9% Quadrant IV

Vehicles registered
between 2001 and 2007
Vehicles registered
between 2008 and 2017

Quadrant I 42.2→41.1%

Numbers after the second number following the7.7→6.2% Quadrant III**: Significance level p < 0.01

Driver vehicle weight (kg)

decimal point are rounded up(survey years 2008-2017)

Fig. 3 - Composition rates for numbers of fatally or seriously injured drivers during vehicle-to-vehicle
frontal collision accidents by age group

3-2.

Changes in numbers of fatally or seriously injured persons and fatality/serious injury rates per
100,000 drivers in their own vehicles
Figure 4 shows the distribution for the number of fatally or seriously injured persons and fatality/serious

injury rates*4 per 100,000 vehicles, with effects from the number of registered vehicles being excluded from thenumber of fatally or seriously injured drivers in their own vehicles. To facilitate comparison, 100 kg increments
are not used. Instead, “from 600 to less than 1,300 kg” and “1,300 kg or more” have each been compiled into
their own separate quadrants.
Although the number of fatally or seriously injured persons per 100,000 vehicles registered between 2008
and 2017 is decreasing more than that for vehicles registered between 2001 and 2007 in each quadrant, bothgroups of registered vehicles are at their highest level for numbers of fatally or seriously injured persons in
Quadrant I, which means some issues regarding accidents between lightweight vehicles remain unresolved.
This is possibly due to factors such as effects from the distribution of elderly drivers or the h igh encounter rate
between drivers of lightweight vehicles.
Furthermore, the fatality/serious injury rate for drivers in vehicles registered between 2008 and 2017 ishigher than that of vehicles registered between 2001 and 2007 in Quadrants I and II. This is possibly due tofactors such as effects from the distribution of elderly drivers shifting to Quadrants I and II. Quadrant II isparticularly high, which means that fatality/serious injury rates are high in accidents between a lightweightvehicle (driver vehicle) and a heavy vehicle (opposing vehicle) and indicates that some compatibility issues
also exist domestically in Japan.
From the above, it is apparent that efforts are necessary that address measures for reducing numbers offatally or seriously injured persons in accidents between lightweight vehicles as shown in Quadrant I, as well as
measures for reducing fatality/serious injury rates for accidents between lightweight vehicles (driver vehicles)
and heavy vehicles (opposing vehicles) as shown in Quadrant II.

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ITARDA 23th Work Shop Report

Macro data
[2001 to 2007] Number of fatally or seriously injured
persons: n = 1,051, Casualty numbers:
n = 9,487[2008 to 2017] Number of fatally or seriously injured
persons: n = 616, Casualty numbers:n = 4,925

Number of fatally or seriously injured persons in macro data
[2001 to 2007] n = 1,051, Number of registered vehicles
between 600 and 1,300 kg: n = 166,758,729,1,300 or more: n = 91,172,529[2008 to 2017] n = 616, Number of registered vehicles
between 600 and 1,300 kg: n = 131,821,684,
1,300 or more: n = 70,825,281

Quadrant II

Quadrant I

Quadrant IV

Quadrant III

Fatality/serious injury rate
Opposing vehicle weight (kg)Opposing vehicle weight (kg)

Number of fatally or seriously injured
persons per 100,000 vehicles

Quadrant II

Quadrant IV

Vehicles registered
between 2001 and 2007
Vehicles registered
between 2008 and 2017

Quadrant I

Driver vehicle weight (kg)

Quadrant III**: Significance level p < 0.01

Driver vehicle weight (kg)(survey years 2008-2017)
Values outside the plots represent vehicles registered between 2001 and 2007, while values inside the plots represent vehicles registered between
2008 and 2017

Fig. 4 - Numbers of fatally or seriously injured persons and fatality/serious injury rates per 100,000
drivers in their own vehicles during vehicle-to-vehicle frontal collision accidents*4) Fatality/serious injury rate = Number of fatally or seriously injured persons ÷ (Fatalities + Serious injuries + Slight i njuries) × 1003-3.

Are measures possible that address both Quadrant I and Quadrant II?
We will now look at measures for addressing the number of fatally or seriously injured persons (QuadrantI) and measures for addressing fatality/serious injury rates (Quadrant II). In the case of Quadrant I—whichshows fatality/serious injuries in collisions between lightweight vehicles—there were many cases of injuries
being caused to the chest or abdomen due to restraining force applied by the seat belt. In order to reduce
numbers of fatally or seriously injured persons, it is necessary to decrease the amount of load being applied tothe chest and abdomen by keeping driver restraining force as low as possible. However, as a measure to addresscollisions between lightweight vehicles (driver vehicles) and heavy vehicles (opposing vehicles) as shown in
Quadrant II, it is necessary to reinforce lightweight vehicle bodies and increase driver restraining force in orderto suppress cabin deformation in lightweight vehicles so that interference to driver steering can be prevented.
Although it is necessary to consider how to implement measures that address both numbers of fatally or
seriously injured persons (Quadrant I) and fatality/serious injury rates (Quadrant II), measures for lightweightvehicles are contradictory as described above, and not easy to achieve.
Conversely, although measures that minimize the harmfulness of heavy vehicle frames by weakening them
are conceivable, there are concerns that simply weakening the bumper beams or frame could result in serious
damage to heavy vehicles (passenger cars) in the event of a collision with a heavy-duty truck or a structure suchas a wall. In response to these concerns, we will continue joint research on compatibility this year and analyze
accidents to observe the harmfulness of heavy vehicles. We will make efforts in cooperation with JAMA toachieve both measures that address both issues by minimizing such harmfulness.
5ITARDA 23th Work Shop Report

3-4. Distribution of parts of the body where drivers in their own vehicles sustained injuries
Figure 5 shows a distribution of parts of the body where drivers in their own vehicles sustained injurie s for eachquadrant. In both Quadrants I and II, drivers sustained torso injuries, such as to the chest and abdomen. Theseinjuries are considered to be an issue particularly providing protection to elderly people who have lower levelsof impact resistance.

Legs

OtherArms

BackLumbar

Abdomen

Chest

Face

Neck

Head

Serious
injuryFatality
Serious
injury

Other

Legs

Arms

LumbarBack

Vehicles registered
between 2001 and 2007
Vehicles registered
between 2008 and 2017

Abdomen

Chest

Neck

Face

Other

Legs

Arms

BackLumbar

Chest

Quadrant III

AbdomenFace

NeckHeadWholebody

WholebodyLegs

OtherArms

BackLumbar

Chest

AbdomenFace

NeckHeadWholebody

Quadrant I

Number of fatally or seriouslyinjured persons (number of people)

Fatality

Quadrant IV

Quadrant II

Wholebody
Head

Number of fatally or seriously
injured persons (number of people)(survey years 2008-2017)

Macro data [2001 to 2007] Numbers of fatally or seriously injured persons: n = 1,051[2008 to 2017] Numbers of fatally or seriously injured persons: n = 616

Fig. 5 - Numbers of fatally or seriously injured persons per 100,000 vehicles by parts of the body where
drivers in their own vehicles sustained injuries4.

Analysis using micro data

4-1.

Details of injuries, points of contact, and extent of injuries sustained by drivers in their ownvehicles
Figure 6 shows a distribution for the number of AIS2+ injuries sustained by drivers in their own vehicles

in a fatal/serious injury accident by injury, points of contact, and extent of injuries*5. From Figure 6, i t can beobserved that when the driver vehicle is lighter than the opposing vehicle, the driver’s chest is injured by theseat belt, while the abdomen is injured by both the seat belt and steering wheel, with bone fractures and visceralinjuries being the most common type of injury sustained. As one of indicator of compatibility evaluations, it
may be effective to emphasize chest and abdomen evaluations while by considering the point of contact and theextent of injuries.
*5) Where the results of micro data are analyzed, it is necessary to pay attention to any impact low amounts of data may have on theaccuracy of results.

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X-axisLumbar fracture

Clavicle fracture

Unknown

LumbarUnknownLiver injury

Kidney injury
Mesenteric injury
AbdomenLung injury

Sternal fracture

Rib fracture

Chest

Tibial fracture
Unknown

Cervical fracture
Cervix

Lower limb

Unknown

Foot fracture

Patella fracture

Hand bone

fractureRadius fracture

Ulna fracture

LumbarUpper limb

Pelvic fracture

Pelvic fracture

Spleen injury

Lumbar fracture

Abdomen injury

injuryMesenteric injury
AbdomenLiver injury

Small intestinal
injuryLarge intestinal

Sternal fracture
Lung injury
Chest

Cervical fracture

Driver vehicle lighter that opposing vehicle(driver vehicle < opposing vehicle)

Upper limb

Unknown
Y-axis Point of contact
Seat belt
No contact (head/neck jerk forward/backward in sudden motion)
Front panel inside
Steering assembly (unknown location)
Steering + air bag
Instrument panel (upper)
15 cases Instrument panel (lower)
Instrument panel

25 casesCervixZ-axisNo. of injuries (AIS2+)(survey years 2005-2017)

Driver vehicle heavier that
opposing vehicle (driver vehicle≧ opposing vehicle)

Micro data[2005 to 2017] AIS2+: n = 40

Vehicles registered
between 2001 and 2017

Part of body where injury sustained

Fig. 6 - Number of injuries sustained by drivers in fatal and serious injury accidents during
vehicle-to-vehicle frontal collisions by injury and point of contact

4-2.

Impact of bumper height differences between vehicles
Figures 7-1 and 7-2 show the relationship that differences in vehicle front bumper height *6 share withnumbers of injuries sustained by drivers in their own vehicles and dashboard intrusion amounts. Whendifferences between bumper heights are small (between -50 to less than 50 mm), dashboard intrusion amountswill also be lower, resulting in fewer injuries with a severity of AIS2+. It is conceivable that effectively
matching bumper heights would improve vehicle-vehicle load transmission and minimize vehicle bodydeformation, in turn resulting in lower numbers of AIS2+ injuries. Although it is apparent that evaluations ofbumper height matching may be effective, joint research performed this year will seek to ascertain whether thatis in fact the case.
Max. intrusion of dashboard
panel (mm)200 or more

150 or more

100 or more

50 or more

0 or more-50 or more-100 or more

-150 or more

Micro data[2005-2017]
AIS1 or lower: n= 51
AIS2+: n = 16

AIS1 or lower (slightinjury/non-injury accident)
AIS2+ (Fatal/serious injuryaccident)

7-1-200 or more

No. of injuries(survey years 2005-2017)

Bumper height difference(= Driver vehicle - Opposing vehicle) (mm)7-2Vehicles registered between
2001 and 2017
Bumper height difference(= Driver vehicle - Opposing vehicle) (mm)Micro data[2005 to 2017] AIS2+: n = 18

Fig. 7 - Numbers of injuries sustained by drivers in their own vehicles/dashboard intrusion amounts invehicle-to-vehicle frontal collision accidents by bumper height difference*6) Bumper height difference = Driver vehicle bumper height - Opposing vehicle bumper height

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5.

Conclusion
In regards to vehicle-to-vehicle frontal collision accidents:(1) It was confirmed that fatality/serious injury rates are high and that compatibility is an issue for theJapanese market when considering measures to address collisions between lightweight vehicles (drivervehicles) and heavy vehicles (opposing vehicles). There are also high levels of chest and abdominal
injuries being sustained, and the protection of elderly drivers is of particular concern in Japan with its
significantly aged population.
(2) On the other hand, it is necessary to continue studying measures aimed at addressing the conventional
issue of perennially high numbers of fatally or seriously injured persons due to chest and abdominal
injuries in accidents between lightweight vehicles.
(3) Because measures for addressing issues (1) and (2) facing lightweight vehicles are contradictory, in thefuture it will also be necessary to analyze accidents to observe the harmfulness of heavy vehicles(passenger cars) in order to achieve measures that address both of these issues, including from theviewpoint of minimizing harmfulness.
(4) Furthermore, in order to standardize compatibility in the future, it may be effective to emphasize chest andabdomen evaluations by considering the points of contact and the extent of injuries, or to use indicatorssuch as evaluations of bumper height matching. We will continue our joint research to ascertain whether
this is in fact the case.

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