The mock civil trial for a hypothetical crash caused by a vehicle with theLevel 2 automated driving system
Satoshi Kitazaki1), Motoyuki Akamatsu2), Makoto Itoh3), Koji Nakayama4), Masayuki Satoh5),
Eiji Yanagawa6), Takashi Hikasa7), Dai Goto8), Naoyoshi Yoshida9), and Shoichi Shibayama10)
1. Introduction
The Automated Driving HMI Committee, consisting of human factors experts from universities and otherresearch institutions, experts from the legal and law professions, experts from industry, and safetyconscious automobile users, had been active for three years from FY2020 to FY2022 in JSAE (Society ofAutomotive Engineers of Japan). The SAE Level 2 Automated Driving System is already being distributed
around the world, however a number of road crashes caused by vehicles with the system have already beenreported. Most of these crashes involved human factors such as drivers’ over-trust or misunderstanding of
the system functions. A fatal crash of Tesla occurred in Yokohama, Japan, in 2018 and the driver of theTesla was found guilty, in the criminal trial, of negligent driving that had caused death and injuries.
Focusing on the crash in Yokohama, the committee delved deeper into the human factors behind the crash.
In order to summarize the discussion, a mock civil trial was held on December 20, 2022 in the courtroomof Meiji University. The aim of the trial was to examine how the legal liability would be determined when
the human factors, especially the limitations of human capabilities, were publicly known. The committee
provided recommendations on what should be done in order to avoid similar crashes in the future.
2. Overview of the fatal crash caused by Tesla in Yokohama
On April 29, 2018, two passenger cars collided in the third traffic lane (fastest lane) of Tomei Expressway,
and a following car (a third car) stopped in the same lane before the spot of the collision. One of the
motorcycles traveling in a group in the same lane failed to detect the stopped third car and crashed with it(pre-occurred crash). Another car (a fourth car) followed by a Tesla approached the pre-occurred crash in
the same lane and changed lane into the second traffic lane in order to avoid the pre-occurred crash.
However, the Tesla accelerated and crashed into the pre-occurred crash. The Tesla killed a rider and injured
two other riders of the motorcycle group who were waiting for a rescue by the pre-occurred crash (Figure1). The Tesla was driving with Autopilot functioning.
The case went to the criminal trial, and the Tesla driver was found guilty of negligent driving that had
caused death and injuries. The obstacle detection function of the Tesla Autopilot was not judged for
defectiveness because it was not clear whether the object detection failure was due to a malfunction or afunctional limitation.
The family of the victim rider subsequently filed a product liability lawsuit in the U.S. District Court in
San Jose against Tesla, alleging defects in the Tesla vehicle. The claim of the plaintiff referred to thehuman factors as the cause of the crash, stating that "Inattention and drowsiness induced driver’s overreliance on the automated driving technology and caused the crash". The claim of the plaintiff also
As of September 7, 2023
1) Business Crea on Department, AIST Solu ons Company. E‐mail: satoshi‐kitazaki@aist‐solu ons.co.jp
2) Human Informa on Interac on Research Ins tute, Na onal Ins tute of Advanced Industrial Science and Technology. E‐
mail: Akamatsu‐m@aist.go.jp
3) Center for Ar ficial Intelligence Research, Ins tute of Systems and Informa on Engineering, University of Tsukuba. E‐
mail: itoh.makoto.ge@u.tsukuba.ac.jp
4) Graduate School for Juris Doctor Course (Law School), Meiji University. E‐mail: nakakoji@tbu.t‐com.ne.jp
5) ITS Japan. E‐mail: m‐satoh@its‐jp.org
6) School of Law, Meiji University. E‐mail: eyana501@meiji.ac.jp
7) School of Management & Informa on Sciences, Tama University. E‐mail: hikasa@tama.ac.jp
8) Harumi Partners Law Firm. E‐mail: gotodai@harumi‐partners.jp
9) Atagoyama Law Oﬃce. E‐mail: yoshida@atagoyama‐law.jp
10) Nihonbashi Shibayama Law Oﬃce. E‐mail: shibayama@mbn.ni y.com

included a reference to a driver monitoring system, stating that "Determining driver’s engagement in thedriving task based only on driver's hands position was defective". This case was dismissed on the grounds
of international jurisdiction (the Japanese court being preferable). However, it was requested to Tesla that
Tesla should accept a service of process provided by a court in Japan, make deposition of witness
available, and make judgment in Japan enforceable both in Japan and in the United States.

Figure 1. Fatal crash caused by Tesla in Yokohama Japan in 2018

3. Mock Trial
3.1 Aim of the Mock Trial
The aim of this mock civil trial (Figure 2) was to examine, using a hypothetical crash scenario caused by a
car with the Level 2 automated driving system, if the legal liability of the manufacturer for inappropriate orinadequate system design and that of the dealer for inappropriate or insufficient explanation about thesystem would be recognized when the limitations of human capabilities for safe use of the system were
publicly known.

Figure 2. Mock trial in the courtroom at Meiji University
3.2 Hypothetical crash scenario
1) Automated driving system
Level 2 hands-on system (product name "Auto Driving System, AuDS")2) Time and place of the crash
Date: 14:00, Friday, September 30, 2022
Location: Near the west side of Numazu Tunnel between Shin-Shimizu IC and Surugawan Numazu IC on
2nd Tomei Expressway towards Tokyo
3) Crash scenario①②③

The subject vehicle entered 2nd Tomei Expressway from Toyota Higashi IC.
The driver soon activated AuDS in the 2nd lane and set the speed at 120km/h.
After passing Shin Shizuoka IC, the driver felt a little sleepy but he believed he could manage till
arriving at Gotemba City which was the goal.

④
⑤
⑥
⑦

⑧

After passing Shin Shimizu IC, the subject vehicle caught up with a truck traveling at about 80km/h
within the 2nd lane and stayed behind the truck by the AuDS (Figure 3a).
Just before Numazu tunnel, the preceding truck changed lane rapidly to the 1st lane.
The driver of the subject vehicle found a dropped object just in front but the subject vehicle began toaccelerate automatically (Figure 3b).
The driver got upset and hurriedly turned the steering wheel, with braking, to change lane to thevacant 1st lane. The subject vehicle lost stability, ran over the shoulder into the slope, and flippedover (Figure 3c).
The driver got his bones broken that caused aftereffects. The vehicle was badly damaged and a vaseof 130K USD being carried by the car was broken.

(a) Scenario ①-④(b) Scenario ⑤⑥(c) Scenario ⑦⑧
Figure 3. Crash scenario4) Other facts
⑨
⑩
⑪

⑫

AuDS had a good reputation. The driver of the subject vehicle interpreted “Auto” of the system nameas a function that would handle a situation like that to avoid a crash automatically.
At the dealer, the driver was explained by a written document about the system features and how to
use the system, and signed the informed consent. There was no verbal explanation about the system.
The driver was not explained sufficiently that the system would not be able to cope with a situation
like that. The driver was not explained either that the car would accelerate automatically in a situation
like that.
The driver was explained that the system was a driver assistance system. He interpreted it as a systemthat would assist the driver to avoid a crash like that.

3.3 Lawsuit Filing
Plaintiff (driver of the subject vehicle) claimed a total of 268K USD (67K USD for the car, 134K USD forthe vase, and 67K USD for the medical treatments) against the manufacturer (Defendant 1) and the dealer(Defendant 2) of the car.
3.4 Claims of Plaintiff (driver of the subject vehicle)
Claim for damages against Defendant 1 (manufacturer) under the Product Liability Act.
The cause of action for this claim is a defects in the vehicle, namely: 1. Defects in the design: (i) despite
the existence of the object, the system generated sudden acceleration towards the object. (ii) safetymeasures were not designed considering decline in alertness of an ordinary driver when AuDS was inoperation. 2. Defects in warnings and instructions: Defendant 1 failed to provide minimum warnings andinstructions for Plaintiff to respond appropriately to the situation that AuDS and Autonomous Emergency
Braking system (AEB) would not be able to handle.
Claim for damages against Defendant 2 (dealer) for damages based on the breach of the contract.
The cause of action for this claim are: 1. Sale of the car with the above defects. 2. Breach of the duty to
explain features of the car with AuDS and AEB so that Plaintiff would understand them and use the car
appropriately.
3.5 Opinions of Appraisers
1) Opinion of Appraiser 1 (human factors expert) about human capability limitations
There are three key points when looking at the course of this crash from a human factors point of view.
First, there is a range of task demand that keeps high alertness of humans. Lower demands than the range
can cause a decrease in alertness. Monitoring task is a typical example for the task with the lower
demands. The Level 2 system requires monitoring task of the driver while the vehicle is controlled by thesystem. It is also generally known that it is difficult for humans to maintain a constant level of alertness
during monitoring tasks, and oversights can increase after 30 minutes of monitoring. Plaintiff had beenusing the system for approximately two hours continuously before the crash and detection of the dropped
object may have been delayed. Second, it is difficult for general drivers to understand system limitations ofdetection of objects other than cars. Daily driving experience with the system detecting front cars securely
can make the driver over-simplify the perceived system function as being able to detect any objects infront. There was a possibility that Plaintiff expected the system to detect the dropped object, resulting in adelay of the avoidance action. Third, when a human receives an unexpected and strong stimulus, he/she
tends to reflexively shrink the body (i.e. the startle reflex). The sudden acceleration of the subject vehicle
towards the dropped object was unexpected vehicle behavior for Plaintiff expecting deceleration. The
startle reflex may have caused Plaintiff to steer abruptly to avoid the object, resulting in the loss of vehicle
control and the crash.
2) Opinion of Appraiser 2 (human factors expert) about importance of education
It is important to provide drivers with appropriate knowledge about necessary driver interventions into
vehicle control when using an automated driving system and a driver assistance system. The tasks to be
performed by the driver, which are dependent on the levels of automated driving, are not well understoodby the general public. Drivers need to understand that Level 2 systems generally have functional
limitations, and the driver must take appropriate actions at those limitations with or without notificationfrom the system. Furthermore, it is important to inform drivers, with representative examples, of situations
where the system may miss or misjudge objects, and actions to take by the driver to cope with thesituations. It is desirable to give drivers an experience driving through such situations, using a driving
simulator or a real vehicle.
In this case, it is questionable how much effort Defendant 1 (manufacturer) made to prevent
misunderstandings of Plaintiff about the driver assistance system. It was possible that Plaintiff
misunderstood the system functions and expected the system being able to assist the driver in any troubles.
Defendant 1 explained "AuDS does not react to objects other than vehicles," but “AEB assists the driver inavoiding collisions with pedestrians, too" which may have caused confusion and misunderstanding of
Plaintiff. There was no explanation by Defendant 1 about what actions driver should take when the system
did not react to non-vehicle objects. Defendant 2 (dealer) only gave written materials on “important
information” and requested Plaintiff to sign the informed consent. No verbal explanations and interactions
were given. It is not always possible for general users to understand wide range of “important information”
through written materials.
3.6 Rebuttals of Defendant 1 (Manufacturer)
Although Plaintiff claimed defects in the system design and defects in warnings and instructions for thedamages under the Product Liability Law, there was no basis for either of these claims. The vehicle was
equipped with AuDS, the Level 2 automated driving system, which had been designed appropriately as adriver assistance system requiring driver’s responsibility for safe control of the vehicle. AuDS assists thedriver by maintaining the vehicle speed at a set one or the headway distance when there is a vehicle infront. Therefore, it was a normal vehicle behavior that the vehicle accelerated to achieve the set speed of
120km/h when the front vehicle (running at 80km/h) disappeared by changing lane. The main cause of thecrash was Plaintiff’s violation of duty for safe driving in that Plaintiff saw the dropped object in his pathand got panicked, resulting in stepping on the brake and turning the wheel abruptly that made the vehicleloose stability and controllability. Installation of safety counter measures for low alertness of ordinary
drivers when using the Level 2 systems was not required by laws and regulations. Plaintiff was obligated tomaintain a certain level of alertness by, for example, immediately taking a rest when he became aware of
declined alertness. However, Plaintiff failed to do so. There were no defects in the system design.
Defendant 1 had been conducting sufficient publicity activities to prevent general users frommisunderstandings of functional limitations of AuDS. Such information was comprehensively written in
the instruction manual. Also, the system was designed to visually display such information each time thepower of the vehicle was activated. Therefore, Plaintiff should have known that AuDS was a driverassistance system and that the driver was responsible for taking appropriate actions when the situation was
beyond the functional limitations of the system. As stated above, Plaintiff should have known the risks inusing the system and could have avoided the risk. There were no defects in warnings and instructions.
3.7 Rebuttals of Defendant 2 (Dealer)
Although Plaintiff claimed breach of the contract of Defendant 2 for the sale of the car with defects in thesystem design, there was no basis for this claim. It was a vehicle that had received proper typecertification. If there had been problems in the system design, the problems would have lain in the typecertification. Also, the instruction manual had been provided by Defendant 1 and Defendant 2 had no
responsibility to explain more than the contents of the instruction manual. Defendant 2 had no
responsibility for the damages in this respect.
Although Plaintiff also claimed breach of the contract of Defendant 2 for inappropriate and insufficient
explanation about feature of the car, there was no basis for this claim, too. Defendant 2 had no
responsibility to prevent users’ misunderstandings about the system caused by media reports. Imposing
such a responsibility on dealers is excessive consumer protection and induces users to abandon their efforts
to understand the system. Defendant 2 fulfilled its responsibility by giving Plaintiff a written explanationof “important information”, that included general information about the system functions, and obtaining
plaintiff's signature on the informed consent. Defendant 2 had not been requested by Plaintiff for further
information. The behavior of the vehicle would not have occurred if the driver’s alertness had been on thenormal level. Defendant 2 did not have a responsibility to explain such behavior in advance. It wasunderstandable for general users that the driver had the responsibility for safe driving with the driverassistance system. Defendant 2 had no responsibility for the damages in this respect.
3.8 Judgment
Conclusion of the Judgement
Defendants shall pay Plaintiff 107K USD. The remaining claims of Plaintiff are dismissed.

Reasons for reaching the conclusion
Issue 1) Defects of the system under the Product Liability Act
The vehicle satisfied the safety standards of the Road Trucking Vehicle Law. The system of the vehicle did
not violate any of the performance guidelines set forth by the national government or industry
organizations. Therefore, no "defect" was found.
The reduction of alertness while driving was an obvious phenomenon from both empirical and ergonomic
viewpoints. However, the primary driver of a car with the Level 2 system was still a human driver, andresponsibility of the human driver for safe driving did not decrease.
Although there is a growing need in Japan and other countries for driver monitoring systems, they are still
under discussion as future solutions.
Issue 2) Duty for explaining the system at the time of sale
Functions, performance, and limitations of the Level 2 driver assistance system are complicated and it isdifficult for drivers to understand all. However, it is possible to increase possibility for the driver to copewith situations like the situation of this case by warning, explaining or letting drivers experience typicaland representative situations in advance.
The primary driver of a car with the Level 2 system is a human driver and the system only “assists” thehuman driver. However, there are vehicle behaviors that are different from driver’s expectations based on
his/her experiences. Expecting drivers to read and understand delivered instruction manual was not
sufficient. A defect in instructions and warnings under the Product Liability Law was recognized forDefendant 1 and a breach of the duty of explanation was recognized for Defendant 2.
Issue 3) Ratio of responsibility (Comparative Negligence)
The primary driver of a car with the Level 2 system is a human driver. Even when AuDS of the vehicle
was functioning and the driver did not need to operate the vehicle control including steering, the driver still
had the responsibility for safe driving.
It was recognized that Plaintiff may have been drowsy. Even if a decrease in alertness or attentiveness wasa natural consequence with the system from ergonomic viewpoints, absence of a device to avoid such a
decrease did not immediately become a defect of the vehicle (already judged in Issue 1), and driver’s duty
for safe driving was not reduced. If the driver had been properly watching the road ahead, he would havebeen able to easily detect and avoid the object. Therefore, Plaintiff bore the primary responsibility for the
injury of Plaintiff and the damages to the vehicle and the vase caused by the crash.
On the other hand, as already judged, responsibilities of Defendants were also recognized. It could not be
overlooked that Defendants’ problematic explanation about the system could have influenced Plaintiff’s
understanding of the system and contributed to occurrence of the crash.
Taking the above into consideration, it is reasonable to consider that the ratio of responsibility is 6:4 forPlaintiff and Defendants.
4 Committee recommendations for the future
The aim of the trial was to examine how the legal liability would be determined when the human factors,
especially the limitations of human capabilities to safely use the Level 2 systems, were publicly known.
The judgment results were that defects in the system design under the manufacturer's liability were notrecognized, while only a part of the responsibility of the manufacturer and the dealer was recognized forthe insufficient and inappropriate explanation on the system. The SAE definition of Level 2 that “theprimary driver of a car with the Level 2 system is a human driver” was effective in the judgment. Based on
the discussion and the judgement in the mock trial, the Committee provides following recommendations toprevent similar crashes in the future.
Recommendations to the Industry

The industry should collaborate with academia to investigate and define limitations of humancapabilities in using the Level 2 system and share them within the industry.



A guideline for Level 2 should be developed in cooperation with the Ministry of Land,
Infrastructure, Transport and Tourism (MLIT). The guideline should include design guidelines tomitigate risks that may be caused by human capability limitations (foreseeable risks).
Manufacturers and dealers/distributors should standardize contents of information given to users
for safe use of the system and methods of explanation for secure and effective understandings ofusers. The information contents should not be the system functions alone but also include
functional limitations of the system, the role of the driver, and the foreseeable misuses in a
concrete form.

Recommendations to manufacturers

Manufacturers should avoid using system names that may mislead users.
Manufacturers should continue efforts to give systems ability to avoid or compensate forforeseeable misuses, including driver monitoring systems.

Recommendations to dealers/distributors


Dealers/distributors should consider effective explanations of the system to deepen understandingsof individual users, such as using the actual system, a simple driving simulator, and animatedimages.
User’s signing on the informed consent should be used as a tool to confirm user's understanding of
the information provided.

Recommendations to users/potential users


Users should make efforts to understand the information provided by the manufacturer and thedealer.
Users should continue efforts, after purchase, to understand the system, especially functional
limitations of the system.

The new committee “Special Committee for Issues related to Engineering and Law in automated driving”
was established in 2023. The committee continues discussion on new safety-related issues arising fromcommercialization of the automated driving technology.