1 Introduction

1.1 Background

Quality transport is required in Japan’s rapidly aging society, which means new mobility services realized by innovative technologies, for example, CASE (connected, automated, shared, and electric) transport services [1]. Self-driving shared vehicles, including autonomous buses (AB), are expected to provide physically or mentally disabled elder travelers occasions to go out by preventing human errors and improving accessibility to transport mode [2]. Presently, the social acceptance of such services is a topic of hot debate and dependent on a variety of economic, demographic, psychographic, service-related, and safety and risk factors [3,4,5,6,7,8,9]. Furthermore, the social and cultural setting in which these studies were conducted may make it difficult to generalize to a Japanese context [10].

Historically, many efforts of seamless public transport services have been devoted mainly in Europe. For example, development plan of vehicles such as Schienen-Straßen-Omnibus enabling through-operation between road and railway has already existed in 1920s [11] and the first curb guided bus system has been operated in Essen, Germany, 1980 [12]. Similarly in Japan, a railway operator began to develop an amphibian bus driving both on road and railway in 1960s [13], a guided busway service started in Nagoya 2001 [14], the dual mode bus was newly introduced in Shikoku 2021 [15]. With recent development and implementation of self-driving technologies, a pilot test of autonomous BRT (bus rapid transit) has been conducted in Kesennuma city [16] that experienced the Great East Japan Earthquake in 2011.

Although many studies have focused on social acceptance toward autonomous vehicles with a sharp development of autonomous vehicles, few have discussed integrating AVs and public transportation and how it might be perceived [10]. Research in this area mostly frames public transportation as an alternative or competitor to AVs, rather than as a supportive component within a city’s technologically advancing transportation network [17, 18]. In cities like Hiroshima, where public transportation is a major part of the transportation system, we should not ignore the mutually supportive relationship between public transport systems and AVs in delivering smart urban mobility and transportation equity [19]. Here, we seek to address these research gaps.

Hiroshima which has 12 bus routes and the longest tram network in Japan is well-known as a transit-oriented development city reconstructed after the bomb in 1945 and a regional center of business and industry in the present day. However, the city is undergoing a wave of aging and depopulation. To ensure social and transportation equity [19], the city is exploring a reform of the public transportation network to seamlessly connect the existing light rail transit (LRT), tram, and bus lines.

As part of this initiative, the authors developed a Virtual Reality (VR) choice experiment of connected public transport between AB and LRT in 2017 [20]. This preliminary study proposed a new scenario of connected public transport network between AB and LRT as shown in Figs. 1 and 2. It was supposed here that ABs run along the LRT track in the congested city center while runs on ordinal roads in uncongested suburbs. However, we were concerned that the choice results from VR experiment may include various biases from actual choice behavior [21,22,23].

Fig. 1
figure 1

Current scenarios: Ordinal bus and LRT operates independently. a) Birds-eye view, b) Horizontal eye view at LRT stop

Full size image
Fig. 2
figure 2

Future scenarios: AB and LRT operated connectedly. a) Birds-eye view, b) Horizontal eye view at LRT stop

Full size image

To address this limitation, the present study reports a pilot test of the aforementioned virtual scenario in the real world. By conducting a monitor survey for the participants in the pilot test and questionnaire SP survey for non-participants (residents), we could examine users’ preference toward self-driving technology and their willingness-to-use the connected AB and LRT. The findings from this study of the world’s first integrated AB-LRT transportation system shows the feasibility to be accepted by the public.

1.2 Outline of Connected Public Transport

As mentioned previously, many bus and LRT routes concentrate in the city center in Hiroshima. Whenever connecting the bus lines to the LRT, passengers must walk from a bus stop to an LRT stop. The inconvenience of the connection between these forms of public transport is a mental and physical barrier for elderly and disabled travelers. At many stops lack a bus-bay, stopping buses often block traffic flow and increase the incidence of congestions and accidents, as shown in Fig. 3.

Fig. 3
figure 3

Present condition of traffic congestion at non-bus bay

Full size image

A newly proposed connected public transport sharing a stop between the LRT and bus lines resolves the inconvenience, as shown in Fig. 4. Given that the bus must drive in and out of the narrow LRT track and follow up and stop before the previous LRT and bus, employing a bus with advanced self-driving technologies and telecommunications equipment integrated with the LRT could ensure safety.

Fig. 4
figure 4

Connection between AB and LRT at a shared stop

Full size image

2 A Pilot Test of Autonomous Bus Proceeding Down in LRT Track

2.1 Outline of Pilot Test

The first pilot test of AB proceeding down in the LRT track was carried out after operating hours of all the buses and LRTs. The details are as follows:

  • Date: November 16 (Sat) to 17 (Sun)

  • Time: 6.5 h from 11:00 pm to 5:30, including preparation and cleanup.

A couple of days before the pilot test, we checked radio wave conditions surrounding the test route, AB control systems, AB braking distance in the track, and also collected the AB trajectory data at the same time slots from November 12 (Tue) to 14 (Thu).

2.2 Test Vehicles

The level 4 self-driving AB used at the pilot test is a bus called “Poncho” by Hino Motors Co., Ltd., shown in Figs. 5 and 6. The specifications of this AB are presented in Table 1.

Fig. 5
figure 5

Seating layout of autonomous bus. (Source: Advanced Smart Mobility Co., Ltd.)

Full size image
Fig. 6
figure 6

Autonomous bus

Full size image
Table 1 Specification of AB “Poncho”
Full size table

During the test, an LRT (Fig. 7) forerunning AB is waiting for the coming AB at Funairi-Kawaguchi Stop Intersection. The AB autonomously stops before the previous LRT and then proceeds precisely down the track by following up on the departed LRT.

Fig. 7
figure 7

LRT (Green Moover LEX-100)

Full size image

2.3 Venue of Pilot Test

The pilot test was conducted at a deregulated section of LRT line #6 (L \(\fallingdotseq\) 225 m), including Funairi-Kawaguchi Stop Intersection (L \(\fallingdotseq\) 25 m), as shown in Fig. 8. At this time in Japan, levels 4 and 5 autonomous vehicles cannot run on public roads. However, the section was specially permitted to operate AB for the pilot test. The cross-section of the target road consists of 5 lanes, i.e., 3 lanes for cars and 2 lanes for LRT track in an A-A cross-section, as shown in Fig. 9. A car lane and 2 LRT lanes were used as a deregulated section.

Fig. 8
figure 8

Deregulated section of LRT track for the pilot test (Digital map by GSI)

Full size image
Fig. 9
figure 9

Geometry design of road section (A-A cross-section)

Full size image

Monitors got in/off the AB at the control center of Eba Terminal. The AB was driven manually for the circuitous route from the control center to the pilot test area (outward L \(\fallingdotseq\) 1.9 km, homeward L \(\fallingdotseq\) 1.0 km) due to legal restraints of autonomous vehicle operation in Japan. Figures 10, 11, 12, and 13 indicate photos of the test sites.

Fig. 10
figure 10

Venue of pilot test (Digital map by GSI)

Full size image
Fig. 11
figure 11

View of deregulated section for AB from Eba (South) to Funairi-Kawaguchi Stop Intersection (North)

Full size image
Fig. 12
figure 12

Entering track, following LRT and exit track

Full size image
Fig. 13
figure 13

Image of AB proceeding down track (Enter track, dock precisely at stop and exit track). (AB was operated in deregulated section (L \(\fallingdotseq\) 225 m) with maximum speed 15 km/hr in track)

Full size image

2.4 Preparation of Pilot Test

2.4.1 Preliminary Safety Check of AB Drive

By taking advice from local police and referring to the “Guideline for Pilot Test of Self-driving System on Public Roads (The National Police Agency, 2015)” [7], a safety check presented in Table 2 was conducted to confirm the feasibility of an AB proceeding down the track.

Table 2 Safety check for AB driving
Full size table

In the final preliminary safety check on the day of the pilot test, we confirmed safe self-driving of ABs based on the conditions presented in the test items in Table 3.

Table 3 Check items of AB self-driving
Full size table

Two cases of AB driving positions relative to the LRT stop shed depicted in Fig. 14 were compared. Consequently, although the AB runs on the bumpy surface of the LRT tracks in Case 1, it did not affect the precise docking control, lane-keeping, and lane changing systems, as shown in Figs. 15 and 16. We rejected an alternative option of a driving position closer to the stop, which would assure more precise docking. The reason being that there should be at least a 483 mm gap from the inner side of the left-hand front wheel of AB to the edge of stop. However, the actual gap with level surface from the bump was only around 400 mm, making this option unsuitable (Fig. 17).

Fig. 14
figure 14

AB driving position. Case1: Body positioned in the center of track. Case2: Left wheels positioned in the center of track

Full size image
Fig. 15
figure 15

AB driving position (Case 1)

Full size image
Fig. 16
figure 16

Precise docking at the stop (Case1)

Full size image
Fig. 17
figure 17

Observed gap from bump to stop edge. [Gap from the inner side of left-hand front wheel to the vehicle side of AB is 283 mm; Degree of GPS accuracy is \(\pm\) 150mm; Margin for door opening/closing is around 50 mm]

Full size image

2.4.2 Protective Measures during the Pilot Test

To maintain security during the pilot test, visible plates “Pilot Program of Autonomous Bus in Tram Track @ Hiroshima” are displayed on the front, side, and rear faces of AB to enable general road users to identify the self-driving vehicle (see Figs. 18 and 19). To case of emergencies such as obstacle avoidance, one driver and one operator were ready to force to stop the AB.

Fig. 18
figure 18

Displayed AB

Full size image
Fig. 19
figure 19

Plates entitled “Pilot Program of Autonomous Bus in Tram Track”

Full size image

During the test, general traffic was restricted not to enter the road section of the pilot test to ensure safety (Figs. 20 and 21). Using safety cones and allocating traffic control staff, the LRT track was enclosed with 2 lanes and a car lane. This ensured that no general cars entered the test section, as shown in Fig. 22.

Fig. 20
figure 20

Traffic restriction at Funairi-Kawaguchi Intersection

Full size image
Fig. 21
figure 21

Traffic restriction from Funairi-Kawaguchi Stop Intersection to the southern Edge

Full size image
Fig. 22
figure 22

Traffic restriction in deregulated section

Full size image

2.4.3 Public Announcement of Pilot Test

The time, date, contents and traffic restriction of pilot test was announced to the residents via their neighborhood associations. And those were also publicly announced to journalistic organizations before the test on November 5 (Table 4).

Table 4 Public Announcement of Pilot Test
Full size table

2.5 Implementation of Pilot Test

The pilot test of connected public transport was conducted for 4 h 10 min from 0:10 to 4:20, excluding preparation and removal time. During that period, a 25-min test drive was repeated 9 times. Each test drive with 8 monitors was conducted following the procedure described in Table 5. In total, 72 monitors took demonstration drives to evaluate the proposed system connecting the AB to the LRT following the schedule presented in Table 6.

Table 5 Procedure of 25-mminute test-drive
Full size table
Fig. 23
figure 23

Boarding monitors

Full size image
Fig. 24
figure 24

AB entering track

Full size image
Fig. 25
figure 25

AB docked at the rear of stop platform

Full size image
Fig. 26
figure 26

AB following LRT

Full size image
Fig. 27
figure 27

Monitors getting in/out AB at stop

Full size image
Fig. 28
figure 28

AB exiting track

Full size image
Table 6 Schedule of monitor survey in pilot test. (2019.11.16–11.17)
Full size table

2.6 Results of AB Pilot Test

2.6.1 Measurement of Test Driving

Data including lateral position, distance (velocity by differentiating with respect to time), lateral error, acceleration (traveling direction), and acceleration (lateral) were observed from 9 repetitive test-drives, as shown in Fig. 29. Table 7 shows the used sensors of self-driving controls.

Fig. 29
figure 29

Relationship between distance and observed data of test-drives

Full size image
Table 7 Sensors of self-driving controls
Full size table

The traveling direction velocities varied during the docking by ACC at the rear of stop and during exiting the LRT track (Fig. 29). We determined that this was due to recognition errors of censors relative to buildings near the LRT stop, traffic security agents, safety cones for traffic restriction, and other factors. The lateral errors tended to have a positive sign, indicating that is the AB most often moved to the left side at stop and were uneven among repetitive drives (Lateral error in Fig. 29).

The traveling direction accelerations varied up to \(\pm\) 0.1G at the departure from a stop during self-driving. On the other hand, lateral accelerations were observed to vary up to \(\pm\) 0.05G at entering/exiting track (see acceleration (traveling direction) and acceleration (lateral) in Fig. 29).

2.6.2 Two-Step Stop

Two-step stop of the AB was autonomously performed by the ACC system before the previous LRT stopping, as shown in Fig. 30. The target distance of the 1st-step stop was set as 6.0 m, and then the AB ran with a slow speed of 20 km/h up to the 2nd stop, which was set to 3.0 m. The errors observed in each of the 9 test drives were considerably different: the 1st-step stop varied from -0.75 m to 2.55 m, and the 2nd-step stop varied from -0.60 m to 2.95 m, as shown in Fig. 30 and Table 8. It appears that these variations were mainly due to identification sensors reacting to surrounding buildings and variation in deceleration by the braking control.

Fig. 30
figure 30

Distance from the previous LRT. (Note: The targets of stop control system were set as 6 m before the previous LRT for 1st-step and 3 m for 2nd-step.)

Full size image
Table 8 Stopping distances from previous LRT
Full size table

3 Questionnaire Surveys for Connected Public Transport

3.1 Monitor Survey and Resident Survey

During the pilot test of connected public transport, we carried out questionnaire surveys (i.e., a “monitor survey”) before and after the test-driving as in Fig. 31. Because of the limited number of 72 samples, a resident survey with a larger sample size was also conducted to test the generalizability of the monitor survey.

Fig. 31
figure 31

Monitor survey

Full size image

The monitor survey comprises a set of prior and posterior surveys (i.e., a panel survey) to the test-driving mentioned in the previous chapter. By comparing them, the changes in perception risks and willingness-to-use (WTU) on the connected public transport can be examined. On the other hand, the comparison of pre-survey for monitors and the resident survey enabled us to analyze and correct the sampling biases inherent in the assessment of risk perception and WTU.

3.2 Outline of Monitor Survey Results

A panel survey for 72 monitors participated in the pilot test was conducted prior and posterior to the AB test-drive experience to examine the change of public acceptance for the newly introduced self-driving bus proceeding down the track and connected public transport between AB and LRT sharing a track and stop.

3.2.1 Sample Profile of Monitor Survey

The age distribution of monitors was almost equal proportions among groups except for monitors in their 30 s, as shown in Fig. 32. However, the gender distribution was unbalanced—the sample was 83.3% male, as shown in Fig. 33.

Fig. 32
figure 32

Age distribution of monitors

Full size image
Fig. 33
figure 33

Gender distribution of monitors

Full size image

In terms of their current travel behaviors, 93% of monitors usually use the existing bus service. But infrequent users of “once a month” (31%) and “every 2 weeks” (16%) were the majority, while only 6.9% of respondents do not use the bus at all (see Fig. 34). In contrast, the number of LRT users was less than bus users. Around 27% of monitors did not have experience using the LRT (see Fig. 35).

Fig. 34
figure 34

Frequency of current bus use

Full size image
Fig. 35
figure 35

Frequency of current LRT use

Full size image

3.2.2 Attitudes to Self-Driving Technology Before and After AB Test-Drive

Most monitors are aware that the advantage of AB service is “Reduction of traffic accidents” both before and after the test-drive. Interestingly, 19% of monitors’ attitudes improved after the test drive regarding the advantage of “Reduction of traffic congestion,” as shown in Fig. 36.

Fig. 36
figure 36

Advantages of self-driving technology

Full size image

In terms of the disadvantage of self-driving technology, the risk of “Unable to flexibly respond to unexpected circumstances” accounted for over 60%. Particularly, it is an intriguing result that risk there was a 12.5% increase on this measure after the test drive, as shown in Fig. 37.

Fig. 37
figure 37

Disadvantage of self-driving technology

Full size image

3.2.3 Positive and Negative Reactions for AB Introduction

93% of monitors reported their acceptance for the introduction of ABs into society, and this figure increased by 4.2% after the test drive (see Fig. 38), indicating feasibility of AB service.

Fig. 38
figure 38

Reaction for and against AB introduction

Full size image

3.2.4 Changes of Willingness-to-use for AB

68% of monitors stated they were willing to use the AB service before the test drive, and which increased by 4.2% following the test drive (see Fig. 39) again, indicating feasibility for the AB service and a benefit from exposure via demonstration.

Fig. 39
figure 39

Willingness-to-use of AB service

Full size image

3.2.5 Evaluation of AB Proceeding down the LRT Track

After the test drive, many monitors stated their positive evaluations of AB driving down LRT track for the items of “Make certain passengers travel with peace of mind”, “Reduce accident risks” and “Make convenient transfers between buses and the LRT” (see Fig. 40). The experienced users tended to have more positive response to the AB policy, suggesting again exposure benefits and the high potential for public acceptance of AB in the future.

Fig. 40
figure 40

Evaluation of AB proceeding down track

Full size image

3.3 Outline of Resident Survey Rresults

A web-based resident survey was carried out for 4 days from March 6 to 9, 2020, in Hiroshima Prefecture to confirm the monitor survey results without explaining the AB. The number of valid samples was 1,035 residents.

3.3.1 Sample Profile of Resident Survey

Like monitor survey, the resident survey aimed to sample an even distribution of age groups, excluding younger generations people in their 20 s (see Fig. 41). The resident survey sample achieved a more equal gender balance, with almost half the sample being female, as shown in Fig. 42. Thus, the following analysis of this survey will help determine an unbiased estimate of the public acceptance of AB.

Fig. 41
figure 41

Age distribution of resident survey respondents

Full size image
Fig. 42
figure 42

Gender distribution of resident survey respondents

Full size image

The frequency of bus users is presented in order of descending prevalence: 41% reporting “Non-users,” 35% reporting “Once a month,” and 9% reporting “Every 2 weeks,” (see Fig. 43). With regard to the main reasons not to use bus services, the percentage of “Private mode available” was highest at 38%, followed by reasons related to inadequate levels-of-services (LOSs) such as “Longer travel time to destination” at 33%, “Unsuitable schedules” at 30%, and “unsuitable routes” at 26% (see Fig. 44). The ratio of non-bus users in this resident survey was 6.9% higher than that in the monitor survey.

Fig. 43
figure 43

Frequency of current bus use

Full size image
Fig. 44
figure 44

Reasons why not to use bus services

Full size image

On the other hand, the percentage of non-LRT users was 51%, followed by “Once a month” at 36% (see Fig. 45). And the main reason not to use the LRT was “Unsuitable routes” (see Fig. 46). The ratio of non-LRT users was much higher than that of non-bus users.

Fig. 45
figure 45

Frequency of current LRT use

Full size image
Fig. 46
figure 46

Reasons why not to use LRT services

Full size image

Together, these findings suggest that there are a variety of issues facing traditional public transportation modes that could will be solved by the future introduction of fully autonomous vehicles.

3.3.2 Risk Perception and Willingness-to-use of AB

Some drive support systems of Level 2 and 3 AVs are already available—namely, the automated braking system, adaptive cruise control system (ACC), and lane-keeping assist system. The history of these advanced systems may affect risk perception of and willingness-to-use ABs. Figure 47 presents the result as of March 2020, in which 16 to 20% of respondents had experience of these systems.

Fig. 47
figure 47

Experiences using driving support systems

Full size image

Over 80% of residents were aware of self-driving or autonomous technologies (see Fig. 48). They acknowledged some advantages of self-driving technology such as “Reduce traffic accidents” and “Saving the troubles of manual driving,” (see Fig. 49), while they recognized the disadvantage of “Unable to flexibly respond to unexpected circumstances” because 47% respondents chose this item (see Fig. 50). These figures closely align with those observed in the monitor survey.

Fig. 48
figure 48

Awareness of self-driving technology

Full size image
Fig. 49
figure 49

Advantages of self-driving technology

Full size image
Fig. 50
figure 50

Disadvantages of self-driving technology

Full size image

3.3.3 Evaluation of AB Proceeding Down Track

70% of monitors agreed with the introduction of AB driving in the LRT track, while 30% disagreed (see Fig. 51). The main reasons for positive responses were “Looks like to reduce traffic accidents,” and those of negative responses were “A fear of accidents by system errors” and “A sense of uncertainty” (see Figs. 52 and 53). Finally, the current public transport users stated their choice intentions between the existing public transport and newly introduced connected AB-to-LRT. The results revealed a virtually equal divide in public opinion toward these transportation technologies (see in Fig. 54). In future research, we will investigate more into public opinions and how they are shaped over time. Based on the other indicators and previous research, it seems that more exposure to and experience with ABs/AVs would improve public opinion toward these technologies.

Fig. 51
figure 51

Reaction for and against AB introduction

Full size image
Fig. 52
figure 52

Reasons why agree with AB implementation

Full size image
Fig.53
figure 53

Reasons why disagree with AB implementation

Full size image
Fig. 54
figure 54

Stated intentions of current public transport users for connected AB to LRT

Full size image

4 Conclusions

This study reports the world’s first physical operation of an AB proceeding down an LRT track. A pilot test of this connected public transport system confirmed the feasibility of implementation advanced self-driving technologies in the real world and demonstrated their likely acceptance. The self-driving technologies enabled the AB to automatically change lanes from the general road to the LRT track, precisely dock at the stop before the parked LRT, follow the previous LRT by keeping within its lane and later exiting from the track to the road again without any assistance of human drivers. Importantly, over 70% of residents reported having intentions to use the AB and public acceptance indicators suggest that it is feasible to implement this integrated AB-LRT system. Social acceptance indicators also looked promising—for example, expectations of accident reductions were raised following exposure to the test drive.

However, there still remain open questions such as the unknown risks involved when operating an AB without human backup in the case of unexpected circumstances. It will be important to keep developing more advanced technologies and infrastructure to reduce these risks and the mental barriers they create.

Altogether, this study marks a significant step forward in introducing ABs into a social system that heavily relies on public transportation. It highlights the possibility of a mutually supportive relationship between autonomous vehicles and traditional public transportation and holds promise for the future of urban mobility and transportation equity. Hence, it could be said that this study holds unprecedented value for “quality transport in the era of auto-sapiens.”