Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
1－Solutions for a New Mobility Society－
Proposal for Safety Analysis and Vehicle Infrastructure
Integration (VII) System for Autonomous Buses

Mobility Business Department
GX Solutions,
Mitsubishi Heavy Industries, Ltd.

The Japanese government expects the realization and diffusion of advanced mobility services
such as Automated Driving Level 4 (fully automated driving under specific conditions) tocontribute to reducing the environmental burden, solving mobility issues, and increasing theeconomic value of the country as a whole, and automated driving projects are being promoted
throughout the country.
Mitsubishi Heavy Industries, Ltd. (MHI) has a wealth of experience in system integration in
the field of transportation systems, and we have been working to resolve issues identified in various
projects through safety analysis and VII systems, utilizing this knowledge.

|1. Introduction
To implement automated driving in society, the Japanese government seeks to achieve
unmanned automated driving transportation services in approximately 50 locations throughout
Japan by Fiscal 2025. The government has launched the "Project on Research, Development,Demonstration and Deployment (RDD&D) of Automated Driving toward the Level 4 and its
Enhanced Mobility Services (RoAD to the L4)" to promote the spread of advanced mobility
services, such as Level 4 automated driving, and has conducted demonstration tests at about 60
locations nationwide in Fiscal 2023. (Regarding automated driving levels, refer to Figure 1)

Figure 1

Levels of automated driving

As a result of the demonstration tests, the following issues could be identified: there is noclear procedure or ideal form of risk assessment, and a system to compensate for the blind areas ofsensors installed in autonomous bus has not been established. MHI believes that proposing a safety
analysis method that utilizes our knowledge of transportation systems and a Vehicle Infrastructure
Integration (VII) system to a society that is advancing toward automated driving will lead not only

Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
2to safety in automated driving, but also to the construction of an efficient system for automateddriving services. We would like to introduce some of these solutions in this report.

|2. Significance of our commitment to automated driving solutions
2.1

Our strengths in transportation systems

MHI has participated in overseas railroad projects as a system integrator, and delivered many
APM (Automated People Mover)/AGT (Automate Guideway Transit)* and metro systems. These
overseas projects required not only construction of a system, but also an objective evaluation of thecompleted system to confirm safe operations. With a proven track record of achieving suchrequirements along with construction work, we feel our experience and technology in thedevelopment of automated railroad projects can be applied to the safety evaluation process andvehicle support systems for the operation of Level 4 autonomous buses (Figure 2).
* An automated transportation system with a rubber-tired dedicated track used around the world fortransportation between airport terminals and nearby facilities.

Figure 2

2.2

Image of MHI’s efforts in the field of automated driving

Predicted issues of autonomous buses and their solutions

In the operation of an autonomous bus, the automated driving control system must perform
various decisions and operations that were previously performed by a human bus driver. In order toidentify and specify the functions required in the system in terms of safety in autonomous bus
operation, considering not only the issues of bus vehicles but also the entire systems at roadsidesuch as bus stops, signal systems, etc., is needed. However, as mentioned above, a procedure toconduct risk assessment has not been established. Therefore, we propose a safety analysis (1) as amethod to evaluate predicted all risks in the operation of autonomous buses, covering each system
including bus vehicles, roadside equipment, and operating conditions such as weather and etc. We
are also developing a support system to detect and compensate blind areas and distant objects noteasily recognized by the automated driving control system as proposed in (2).
(1) Safety analysis (an analysis method used for overseas metros and APMs/AGTs applied toautonomous bus systems)
Safety is analyzed and evaluated in order to identify the functions necessary for theplanning of an autonomous bus system. This analysis is also used as an objective
evaluation at the start of operations.
(2) VII system
Various types of information on the road and along the route, which cannot be recognizedby bus vehicles, are collected using sensors installed on the roadside and then transmitted
to the autonomous buses, leading to improved safety and efficiency in the operation ofautonomous buses.

|3. Safety analysis
3.1

Overview of safety analysis

We propose a PHA (Preliminary Hazard Analysis)-based safety analysis method to consider
safety assurance of the autonomous bus system planning. The PHA predicts possible risks arisingMitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
3from hazards to each system at the system planning stage, evaluates each risk level based on
frequency of occurrence and severity of the risk, and considers measures to reduce such risks.

3.2

Characteristics of safety analysis

This safety analysis can evaluate predicted risks to some extent quantitatively and classify
them into risks that are intolerable and risks that can be tolerable (acceptable with adequate control
and the agreement) and consider measures of mitigation effectively. In addition, this safety analysis
can determine the degree in which risk reduction measures have improved the risk level from theinitial state as the residual risk, and can specifically represent the status of improvement.
For example, a sudden appearance of vehicles, etc. from blind areas that cannot be identified
by the autonomous bus can be organized as a hazard, a contact accident with vehicles suddenly
appearing is a risk, and an information transmitted by the VII system is a measure of mitigation.

3.3

Benefits of the safety analysis

By reflecting the results of the PHA for autonomous buses and roadside equipment to reduce
the risk of accidents, highly safe autonomous bus system can be realized. In addition, the extracted
risks and their measures of mitigation can be visualized, and as a result, this perception of safety
can be shared with various stakeholders related to the autonomous bus system. This has beenhighly praised by customers in the past for its usefulness in discussions involving management
layer.

|4. VII system
4.1

Overview of VII system

This system uses cameras installed on roadsides to detect vehicles and other objects aroundan autonomous bus and transmits the information to the autonomous bus entering an intersection
for improved control of automated driving. This system can be used in a wide range ofapplications, such as identifying objects suddenly appearing from blind areas and detecting
oncoming vehicles when an autonomous bus makes a right turn at an intersection. As mentioned in
the above safety analysis, there are still some risks when only the sensors installed on an
autonomous buses are used. By conducting actual demonstration tests focusing on objects suddenly
appearing out of a blind area and safety assurance at intersections with poor visibility, we could
confirm the likelihood of risks and the need for measures of mitigation.
The purpose of this system is to improve the safety of automated driving of autonomous
buses by transmitting information regarding road traffic conditions that is difficult for theautonomous buses to recognize, based on AI analysis of roadside camera images (Figure 3). For
example, when a vehicle approaches from a side road while an autonomous bus is going straight
through an intersection, the VII system transmits information regarding the type of the approachingvehicle, its speed, and its location to the autonomous bus, allowing the bus to accurately understandthe road traffic conditions and drive safely.
In another example, when an autonomous bus makes a right turn at an intersection, if there isan oncoming vehicle waiting in the right-turn lane, it is difficult to detect oncoming vehicles thatenter the intersection going straight (Figure 4). In this situation as well, the VII system transmits
information regarding oncoming vehicles to the autonomous bus allowing it make a right turnsafely and to prevent collision with oncoming vehicles going straight.

Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
4Figure 3

VII system demonstration test

Figure 4 The autonomous bus cannot see oncoming vehicles going straight due to theoncoming truck waiting to make a right turn. The photo is an example forfurther understanding. (Image)

4.2

Features of VII system

There are various types of roadside detection sensors, such as cameras, LiDARs, andmillimeter wave radars. From these, by adoption of camera sensor, we have developed a system toprovide information on speed, position, and object type to autonomous buses at a relatively lowcost. In addition to sensed detection information, image data can also be transmitted, not only toautonomous buses but also to buses with a human driver. This is expected to improve operationalsafety.

Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
54.3

Benefits of VII system

By providing information regarding vehicles on the road located in the blind spots ofautonomous buses, pedestrians crossing at intersections, etc., motorcycles traveling on the side ofthe road and other crucial information, we believe that this system will contribute to improved
safety in the operation of autonomous buses.

|5. Future prospect
This report introduces our efforts in safety analysis and a VII system for the safe operation ofautonomous buses. Going forward, we will continue to improve the reliability of this method andsystem by further collecting data through participation in demonstration tests, etc. Thus, we would
like to apply this method and system to the actual operation of Level 4 automated driving ofautonomous buses.