ITARDA 23th Work Shop Report

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

Analysis of Accidents in Right turn across path (for left-hand traffic) Between Cars andMotorcycles at Night
Yojiro Tsutsumi
Senior Researcher, Research Division

1

ITARDA 23th Work Shop Report

1. Background

95% of casualties in motorcycle accidents (total of primary and secondary parties) occur due to vehicle-vehicle
accidents (total from between 2015 and 2019; information shown below is for this time period). In 92% of thesevehicle-vehicle accidents, the opposing vehicle is a car, meaning that most motorcycle accidents involve amotorcycle and car. Furthermore, crossing collisions are the most common type of accident, with accidents in rightturn across path being the second most common type. The fact that accidents in right turn across path—uncommon
in the case of accidents between cars—are so common in the case of motorcycle accidents is one of the main featuresof accidents in right turn across path (Fig. 1). In 91% of accidents in right turn across path involving a motorcycle
and a car, the car is the right-turning vehicle and is the primary party (i.e., the driver involved in the accident withthe most negligence; when negligence is the same, the driver that suffered the least amount of personal injury is thetraveling vehicle and is the secondary party. In thisresearch, we analyzed this type of accident in rightturn across path. Also, when looking at which typesof motorcycle accidents tend to occur in thedaytime and which tend to occur at night, it can be

Number of casualties

primary party), while the motorcycle is the straight-

seen that accidents in right turn across path are themost common type of accident that occurs at night.
Although numbers of motorcycle rider casualties(total of primary and secondary parties) due toaccidents in right turn across path that occur in theFig. 1 - Number of motorcycle rider casualties by type ofaccident (total of primary and secondary parties)(vehicle-vehicle accidents involving a car and a motorcycle)

the same (Fig. 2), the risk of such accidents ishigher at night as described above. In this research,
we focused on accidents in right turn across paththat occur at night and analyzed the features ofaccidents in right turn across path in an attempt toNumber of casualties

daytime and those that occur at night are roughly

find ways to reduce such accidents.
Among the human factors cited in accidents inright turn across path in which the primary party
Daytimewas a right-turning car, “delay in noticing” madeup 88%, while “misjudgment” made up theremaining 12%. Because these two causes areNightFig. 2 - Number of motorcycle rider casualties by type ofaccident (total of primary and secondary parties)(vehicle-vehicle accidents involving a car and a motorcycle)

considered to be different, we analyzed "delay innoticing" and "misjudgment" separately.
In subsequent analysis, we will be using the term “accident risk”. An indicator which showing how manydrivers have the opportunity to drive on how many roads is referred to as “induced exposure”.
However, because there is no statistical data that can be used directly, we will be using other types of data in its2

ITARDA 23th Work Shop Reportstead. One such type of data is “number of secondary parties that did not commit a legal violation”. Past
research(1) exists which has shown that the number of secondary parties who did not commit a legal violation is
proportional to the “induced exposure”. With this in mind, in this research, we assessed the risk of an accident
occurring by dividing the “number of driver casualties” by the "number of non-negligent secondary parties”.
In this research, we refer to this risk being the “accident risk”. It is necessary to keep in mind that the value foraccident risk is a relative value that is helpful when making comparisons within the group being analyzed.

2. Accidents in right turn across path due to “delay in noticing”
Shown below is analysis performed when “delay in noticing” is the human factor responsible for an accident
in right turn across path involving a right-turning car. From 2015 to 2019, the total number of motorcycle rider
casualties was 22,889 in the daytime and 17,644 at night. Furthermore, the “number of secondary parties that did
not commit a legal violation” among those riding a motorcycle totaled 74,854 in the daytime and 32,779 at night.
Using these to calculate accident risk gives 0.31 in the daytime and 0.54 at night. This shows that the accident risk
at night is 1.8 times that of in the daytime and means that the risk of an accident in right turn across path occurring
at night is considerably higher than in the daytime.

straight-traveling motorcycle had in accidents inright turn across path that occurred in both thedaytime and at night. We found that the majority ofAccident risk

We then analyzed what influence the speed of

motorcycle rider casualties occurred at around 30
km/h in both the daytime and at night. Furthermore,when looking at accident risk, we found that
accident risk in both the daytime and at night

Danger perception speed of straight-traveling motorcycle
Accident risk indaytimeincreased as speed increased (Fig. 3). Here,
accident risk is calculated by dividing “number ofmotorcycle rider casualties by straight-traveling

Accident risk atnight

Fig. 3 - Accident risk by danger perception speed
due to “delay in noticing”

motorcycle danger perception speed” by “number of secondary parties that did not commit a legal violation by
danger perception speed” among those riding a motorcycle. Why do the drivers of right-turning cars experience adelay in noticing straight-traveling motorcycles moving at a high speed, the result of which is an increase in accident
risk? We made the following observations regarding this question. In order to avoid an accident in right turn acrosspath, the driver of the car waiting to turn right must notice the straight-traveling motorcycle driving when themotorcycle is at a distance that is
proportional to its speed. In otherMotorcycle

words, if we assume that it takes 3

Motorcycle

Assuming it takes 3
seconds to decide to turnright and proceed to crashlocationseconds for the driver of a car that has
Four-wheeled vehicles
waiting to turn rightdecided to turn right to make the rightturn and proceed to the crash location,
the driver of that car must notice any
straight-traveling motorcycle moving at aFig. 4 - Relationship between straight-traveling motorcycle
speed and distance3

ITARDA 23th Work Shop Report

speed of 30 km/h when that motorcycle is 25 m or more ahead in order to avoid an accident in right turn across path.
Similarly, when the speed is increased to 60 km/h, it is necessary for the motorcycle driving straight ahead to be
noticed when it is 50 m or more ahead (Fig. 4). Noticing a motorcycle that is far away is more difficult than noticing
a motorcycle that is nearby, which is understandable considering the view angle from which the motorcycle is seenby the driver of a right-turning car. The view angle of a motorcycle that is far away will be small, while that of amotorcycle that is nearby will be comparatively larger. Recognizing the existence of something with a small view
angle is difficult, and delays in noticing such objects is a cognitive characteristic of human beings.
Next, by looking at the day-night ratio of accident risk, it can be seen that when the speed of a straight-travelingin a higher accident risk at night than in thedaytime. When the distance between a rightturning car and a straight-traveling motorcycleis short (at a slow speed), it appears to besignificantly more difficult for the driver tonotice a straight-traveling motorcycle at night
than in the daytime. Conversely, when theAccident risk at night ÷ Accident
risk in the daytime

motorcycle is low, the day-night ratio (accident risk at night ÷ accident risk in the daytime) will be large, resulting

distance is long (at a fast speed), it appears there
is little difference in noticing whether it be atDanger perception speed of straight-traveling motorcyclenight or in the daytime (Fig. 5).

Fig 5. - Day-night ratio of accident risk by danger
perception speed

When the distance is short, it is easier for drivers

to notice motorcycles in the daytime because the motorcycle and its rider are more visible, while at night only theheadlights are conspicuous, making noticing more difficult. Furthermore, when the distance is long, parts of themotorcycle other than the headlights are not as conspicuous even in the daytime, creating a situation that is almost
the same as at night, leading us to assume that the difficulty drivers have in noticing motorcycles does not change
significantly between day and night. Accordingly, it is necessary for extra attention to be paid at night, even whenspeeds are slow.

4

ITARDA 23th Work Shop Report

Finally, we analyzed what influence the age ofAccident risk

the driver of the right-turning car had in accidents
in right turn across path that occurred in both thedaytime and at night. When looking at what
influence age had in accident risk, we found thataccident risk was higher at night than in the daytime
regardless of age group. Furthermore, we found that
accident risk was considerably higher for elderly

Age of right-turning car driver
Accident risk indaytime

groups than that of middle-age groups at both night
and in the daytime. Here, accident risk is calculated

Accident risk atnightFig. 6 - Accident risk by right-turning four-wheeledvehicle driver age group due to “delay in noticing”

by dividing “number of motorcycle rider casualties

by right-turning car driver age group” by “number of secondary parties that did not commit a legal violation by age
group” among those driving a car. In the daytime, the accident risk for people aged 75 and older is 3.3 times higher
than the accident risk for people aged 35 to 44, and at night, this ratio increases to 5.2 times (Fig. 6). This meansthat a marked increase in accident risk due to age is seen at night when compared to in the daytime. It appears thatthe elderly may have a lower cognitive ability to notice motorcycles than middle-age groups, especially at night,
meaning it is imperative that immediate action be taken for the elderly.

3. Accidents in right turn across path due to “misjudgment”“misjudgment” is the human factor responsible
for an accident in right turn across pathinvolving a right-turning car. From 2015 to2019, the total number of motorcycle rider

Accident risk

Shown below is analysis performed whencasualties was 2,981 in the daytime and 2,474 atnight. Furthermore, the “number of secondary
parties that did not commit a legal violation”

Danger perception speed of straight-traveling motorcycle

Accident risk indaytime

totaled 74,854 in the daytime and 32,779 atnight. Using these to calculate accident risk
resulted in 0.040 in the daytime and 0.075 at

Accident risk atnight

Fig. 7 - Accident risk by danger perception speed due to“misjudgment”

night. Accident risk at night is 1.9 times that in
the daytime, and it can be seen that the risk of accidents in right turn across path at night is considerably higher thanin the daytime in the same manner as “delay in noticing”.
We then analyzed what influence the speed of straight-traveling motorcycle had in accidents in right turn acrosspath that occurred in both the daytime and at night. When looking at accident risk in the daytime and at night, wefound that accident risk increases as the speed increases in both the daytime and at night and in the same manner as“delay in noticing”. However, compared to “delay in noticing”, the influence of speed in the case of “misjudgment”
was considerably stronger, with this influence being even stronger at night than in the daytime (Fig. 7). In the caseof "delay in noticing", the accident risk at night at a speed of 80 km/h or less is 1.4 times that when 40 km/h or less.
5

ITARDA 23th Work Shop Report

However, in the case of “misjudgment”, the accident risk at night at a speed of 80 km/h or less is 4.9 times thatwhen 40 km/h or less. In this way, the influence of speed on accident risk at night due to "misjudgment" is strong,
and it appears that it in order to reduce accidents, it is more important to reduce the speed of straight-travelingmotorcycles than in the case of “delay in noticing”. One factor of “misjudgment” is “misjudgment of speed and/ordistance”. Although it is necessary for drivers to make accurate judgments regarding the speed and distance of a
distant, fast-moving motorcycle in order to avoid an accident, it has been observed that human cognitive
characteristics can make such judgments difficult, meaning this is a possible cause for the strong influence speed
has on accident risk due to “misjudgment”.

driver of the right-turning car had in accidents inright turn across path that occurred in both thedaytime and at night. When looking at what

Accident risk

We then analyzed what influence the age of theinfluence age had in accident risk, we found that
accident risk was higher at night than in the daytime
regardless of age group. Furthermore, we found that

Age of right-turning car driver

accident risk was considerably higher for elderly

Accident risk indaytimegroups than that of middle-age groups at both night
and in the daytime. When compared with “delay innoticing”, it was found that accident risk in theAccident risk atnightFig. 8 - Accident right by right-turning car driver age
group due to “misjudgment”

daytime increased the older the driver. In thedaytime, the accident risk for people aged 75 and older is 5.3 times higher than the accident risk for people aged 35
to 44, and at night, this ratio increases to 5.7 times (Fig. 8). Furthermore, in the case of “delay in noticing”, the ratioof accident risk in the daytime is also 3.1 times higher, with this ratio increasing to 4.9 times at night.

4. Direction of accident reduction measures of accidents in right turn across path
Accidents in right turn across path are the most common type of accident at night and accident risk at night isapproximately double that of in the daytime. Accident risk increases in proportion to straight-traveling motorcycle
speed and we observed that the influence of straight-traveling motorcycle speed was even stronger in accidents
where the human factor of “misjudgment” was to blame. In the case of “delay in noticing”, accident risk is higher
at night than in the daytime even at low speeds (30 to 40 km/h). Furthermore, the accident risk faced by elderly
drivers of right-turning cars was higher than that faced by other age groups. This is especially true at night, with it
being observed that accident risk is 5 times higher for later-stage elderly drivers (75 or older) at night than for drivers
aged 35 to 44. Although accidents in right turn across path have been a significant portion of all car accidents foryears, few concrete measures to address such accidents have been implemented. Based on the features of accidents
in right turn across path clarified by this study, we would like to propose the following aims for measures designed
to reduce accidents in right turn across path between cars and motorcycles.

6

ITARDA 23th Work Shop Report<Motorcycles>
Soft measure: Motorcycle riders should be advised to reduce their speed when they encounter a car that iswaiting to turn right, particularly at night.
Hard measure: A system that enables drivers to more quickly notice straight-traveling motorcycles even fromfar away should be urgently developed. Such a system could include the use of lights that
improve the conspicuity of motorcycles (e.g. yellow-colored headlights/high-intensity
lights/light arrangements that make the motorcycle seem larger in appearance).
<Cars>
Soft measure: Drivers of cars should be educated regarding the fact that it is easy to miss the presence of astraight-traveling motorcycle, especially at night, and that a sufficient amount of time isnecessary to perform a safety check to confirm that there are no straight-traveling opposing
vehicles.
Hard measure: Because elderly drivers face a higher accident risk than drivers in other age groups, hardmeasures that target the elderly—including ever more efficient systems designed to suppress
accidental acceleration—may be necessary in addition to the measures described above. Brakesystems (systems that avoid or mitigate crashes by detecting the movement of an oncoming,
straight-traveling vehicle) that work to mitigate crashes with oncoming vehicles when turning
right have begun to be installed in cars and the increased adoption of such systems is urgentlyneeded. Furthermore, the development of functions that warn drivers of oncoming/approachingvehicles utilizing road-to-vehicle communications may also prove effective in reducing suchaccidents.
References(1) 西田 泰：交通事故分析に基づく交通行動特性の把握手法に関する研究，
公益財団法人日本交通政策研究会 （A-538, 2012 年 2 月）

7