Three Lines Disappeared on the Same Day

When heavy rain falls, lines disappear from the map of Setouchi.

The Shimanami Expressway—a 60 km long toll road connecting Onomichi and Imabari—was closed. The Sanyo Shinkansen—approximately 280 km between Hiroshima and Hakata—halted operations. And the Nishikigawa Railway—a local line spanning 32.7 km connecting Nishikimachi in Iwakuni City and Shinyakuni—suspended service for the entire day.

These three lines, differing vastly in scale and function, all stopped on the same day. This is not a coincidence. It illustrates how few threads hold the Setouchi region together.

The Quiet Fear of “No Alternatives”

When the Shimanami Expressway is closed, the only means of traveling between Onomichi and Imabari is by ferry. However, during inclement weather, those ferries may also be canceled. This creates time periods where the route connecting Honshu and the islands of Shikoku literally becomes zero.

Oshima, Hakata Island, and Oshima Island—about 20,000 people live on the islands along the Shimanami Expressway. What happens if an emergency arises that cannot be handled at the island’s clinic? It would be fortunate if the weather allowed for a doctor helicopter to be dispatched. But if heavy rain and strong winds coincide, the helicopter cannot fly. The fact that there are “no alternatives” is invisible during normal times. It only becomes apparent at the moment everything stops.

When the Sanyo Shinkansen halts between Hiroshima and Hakata, the impact is on a different scale. According to data released by JR West, the daily passenger count for the Sanyo Shinkansen is about 180,000 (based on 2023 figures). A considerable number of passengers are stranded even just on the Hiroshima-Hakata route. While alternative transportation is concentrated on the conventional Sanyo Main Line, it lacks the capacity to absorb Shinkansen passengers, especially in sections that include single-track lines. The platforms for conventional lines at Hiroshima Station overflow with people, and reservations for express buses fill up instantly. Business travelers search for accommodations, and tourists rearrange their schedules. Each of these situations reverberates back to the local economy in the form of accommodation costs, cancellation fees, and lost opportunities.

What Becomes Invisible When the Nishikigawa Railway Stops

The third line—the Nishikigawa Railway’s all-day suspension—receives the least coverage in the news. However, as an editor, this was the aspect that concerned me the most.

The population along the Nishikigawa Railway is about 4,000, many of whom are elderly. The average daily ridership is only about 300. Looking at the numbers alone, one might write that “the impact is limited.” However, for those 300 people, the Nishikigawa Railway is their means of getting to medical appointments, shopping, and visiting grandchildren. The alternative bus service is infrequent, and the number of taxis is limited. For elderly individuals without private vehicles, the railway’s suspension means “I cannot leave my house today.”

When the Sanyo Shinkansen stops, it becomes national news. When the Shimanami Expressway halts, it spreads as tourist information. However, the fact that the Nishikigawa Railway has stopped hardly reaches anyone outside the local residents. The disruptions that go unreported are also easily overlooked in terms of prioritizing responses. Here lies another structural issue regarding the vulnerability of transportation networks—”what is invisible is difficult to protect.”

Viewing the Setouchi Transportation Network as a “Surface”

When we line up these three routes, we can begin to see how the transportation network in Setouchi is structured.

The Sanyo Shinkansen is the “spine.” It is a major artery running east to west, connecting urban areas such as Hiroshima, Okayama, and Kitakyushu at high speeds. The Shimanami Expressway serves as the “ribs.” It is one of the few routes that crosses the Seto Inland Sea southward from the spine to Shikoku. While there are three bridges connecting Honshu and Shikoku, the Shimanami Expressway is the only route that allows direct access from Hiroshima Prefecture to Shikoku. The Nishikigawa Railway acts as the “capillaries”—thin tubes branching off from the spine, delivering blood to rural communities in the mountainous areas.

If the spine breaks, the entire body becomes immobile. If the ribs break, breathing becomes difficult. If the capillaries become blocked, only the individual is aware. However, the tissues beyond the blockage are certainly headed toward necrosis.

The problem is that these three layers are operated by separate entities. The Sanyo Shinkansen is managed by JR West, the Shimanami Expressway by Honshu-Shikoku Bridge Expressway Company, and the Nishikigawa Railway by a third-sector entity. Decisions regarding recovery during disasters and information dissemination are carried out at the standards and speeds of each organization. While it may appear as a single “movement” from the user’s perspective, it is viewed as separate “businesses” from the operational side. This gap amplifies confusion during disasters.

The Design Philosophy of Redundancy

In the field of transportation engineering, there is a concept known as “redundancy.” It refers to a state where, even if one route is cut off, functionality can be maintained via another route. In major urban areas like Tokyo and Osaka, railways, buses, subways, and expressways are intricately woven together, providing detours even if one line stops. Redundancy is high.

What about Setouchi? There are three routes connecting Honshu and Shikoku. There is only one direct route from Hiroshima Prefecture to Shikoku. There is one railway to the mountainous areas. Redundancy is structurally low.

So, should we increase alternative routes? The situation is not that simple. The construction cost of the Shimanami Expressway was about 750 billion yen. Building another bridge would incur similar or higher costs. The Nishikigawa Railway has an annual operating revenue of about 100 million yen, while its operating costs are several times that amount. In reality, it is maintained while covering its losses. There is no financial capacity to draw “another line.”

This is why the focus should be on how to “reconnect” existing infrastructure. Rather than increasing hard infrastructure, we should ensure redundancy through soft solutions. Specifically—agreements for alternative transportation that automatically activate during disasters, systems for sharing information across municipalities, and the visualization of local transportation resources, including ferries and fishing boats. Such “systemic redundancy” will become the only realistic solution to compensate for the lack of physical infrastructure.

What the Evacuation Information for the Elderly in Etajima Reflects

During this heavy rain, evacuation information for the elderly was issued across all of Etajima City. With a population of about 21,000 and an aging rate of about 45%, this means that the judgment to evacuate was left to approximately 9,500 elderly individuals.

Etajima is an island. The only connections to the mainland are the Hayase Bridge and ferries that depart from Kiri and Koyou. If the ferries are canceled due to heavy rain, the bridge becomes the only escape route. That bridge may also be subject to traffic restrictions based on wind speed and rainfall.

“Evacuation for the elderly” is one step before the evacuation order. It is information encouraging early action for those who may take longer to evacuate on their own. However, when the means of transportation itself is cut off, telling someone to “evacuate early” may not be feasible. The dissemination of information and the securing of transportation must be designed as a set. Here, too, there is a gap in the system.

Climate Change and “The Next Heavy Rain”

According to data from the Japan Meteorological Agency, the annual occurrence of “very heavy rain” with hourly precipitation of 50 mm or more has increased by about 1.5 times compared to the average from 1976 to 1985. The Setouchi region is no exception. In the 2018 Western Japan Floods, over 100 people lost their lives in Hiroshima Prefecture alone. Disruptions to transportation networks lasted for weeks.

“The next heavy rain” could be next year or next month. At that time, there is a significant possibility that the same three lines will disappear simultaneously again. What is being questioned is how quickly we can establish alternative measures after they stop—and how we can deliver support to the areas along the routes that may not even be reported.

Counting the Number of Threads

The “connections” in Setouchi are held together by far fewer threads than one might think. The spine of the Shinkansen, the ribs of the Shimanami Expressway, and the capillaries of the Nishikawa Railway—when each of these threads breaks, the one who suffers most differs. If the Shinkansen stops, business travelers are inconvenienced. If the Shimanami stops, the island residents are affected. If the Nishikawa Railway stops, someone living alone in a mountain village may have to give up their medical appointment for the day.

The vulnerability of the transportation network can be measured in numbers. However, what we should truly see is the “daily movement” of each individual behind those numbers. The system exists for the people. When the system stops, how do we reach out to those who cannot raise their voices first?

On the day when the three lines disappeared simultaneously—the fact that this occurred raises questions not about the strength of the infrastructure, but about the range of our imagination.