Measuring the Coverage–Accessibility Decoupling in Post- Earthquake Transport Networks: Lessons from the 2026 Kumamoto Earthquake

When a major earthquake strikes, the first question from the public is often simple: are the roads open? Emergency crews rush to clear debris, and officials begin counting the kilometers of highway that have been repaired. For years, the standard way to measure recovery has been to look at that number of open kilometers. If a hundred miles of road are clear, the assumption is that the region is moving again. But this approach misses a crucial detail. A road can be open for a car to drive on, yet if that road does not connect to the places where people actually live, work, or go to school, the community remains cut off. The distance between a road being physically open and a community being functionally connected is the gap researchers are now trying to understand. This is the difference between coverage, which is simply the length of road available, and accessibility, which measures how easily people can reach their destinations.

In the wake of the July 28, 2026, Kumamoto earthquake, a team of researchers set out to measure this gap. The earthquake, a powerful event centered near the city of Kumamoto in southern Japan, damaged both the highway network and the railway lines that run through the same valley. As the days passed, officials released a steady stream of reports detailing which sections of the expressway were open to emergency vehicles and which were open to the general public. The researchers took these official reports and combined them with data on where people live and how they travel. They built a digital map of the region, not just to count the open miles, but to simulate whether a person in one town could actually reach a person in another. Their goal was to see if the official story of recovery matched the reality on the ground.

The findings revealed a significant disconnect. By August 15, eighteen days after the quake, the official reports stated that 85 percent of the restricted expressway length was open to general traffic. By the traditional metric of coverage, the highway system was nearly restored. However, when the researchers calculated accessibility—taking into account the population and where people needed to go—the number was much lower. Only 58 percent of the system's potential for movement had been restored. The highway was open, but the network was still broken in a way that mattered most to the people living there. The problem was not a lack of open road, but a specific missing piece.

The culprit was an eight-kilometer connector road at the Yatsushiro Junction. This short stretch of highway links two major sections of the expressway. On August 15, this connector remained closed to general traffic, even though the longer stretches of road on either side had been reopened. Because this connector was closed, a large portion of the city of Yatsushiro was effectively an island. People could drive on the highway, but they could not cross from one side of the city to the other without leaving the expressway system. The researchers found that opening just this one eight-kilometer section would have raised the accessibility score significantly, reconnecting the split communities and allowing people to reach their daily destinations.

This discovery highlighted a conflict in how recovery should be prioritized. If the goal is to move the most vehicles possible, the data suggested a different path. Another section of highway, fourteen kilometers long, was open only to emergency vehicles. This section carried a much higher volume of daily traffic than the connector. If officials had focused on opening that longer fourteen-kilometer stretch first, the total amount of traffic the highway could handle would have increased more than if they had opened the connector. However, doing so would have left the city of Yatsushiro still divided. The longer road would have created a dead-end for local residents, while the connector would have kept the city whole. The researchers showed that the choice of which road to fix first depends entirely on the goal: maximizing traffic flow or restoring community connection.

The same pattern appeared in the railway system. The high-speed Shinkansen line, which runs parallel to the highway, also suffered a break in the middle of the corridor. By August 15, 70 percent of the railway line was open, but the break was located exactly where the highway connector was missing. This meant that even if a traveler switched from a car to a train, they still could not cross the gap. The railway and the highway were failing in the same place, creating a single, deep cut through the region's transportation network. The researchers noted that until this central block was repaired, the two modes of transport offered no real alternative to one another.

The study also challenged the way we view the very first hours after a disaster. On the evening of the earthquake, officials listed many road sections as "under inspection." In the past, these unknowns might have been treated as total failures, suggesting the entire network had collapsed. The researchers argued that this was an overstatement. Instead, they treated the unknown status as a range of possibilities. On the first night, the network was not necessarily broken; it was simply uncertain. As more information came in over the following days, the uncertainty shrank, and the true state of the network became clear. This approach showed that the recovery of function lagged behind the recovery of length. The roads were being measured as open faster than the people were being able to use them effectively.

Ultimately, the paper demonstrates that counting open kilometers is not enough to tell the story of a region's recovery. A road can be open and still leave a community stranded. The 2026 Kumamoto earthquake showed that the most critical repairs are not always the longest ones or the ones with the most traffic. Sometimes, the most important fix is the shortest link that holds a city together. The researchers concluded that if the goal is to help people get back to their daily lives, the priority must be the connector that re-establishes local access, even if it means the total traffic volume on the highway grows more slowly. The lesson is clear: restoration is not just about the road; it is about the people who need to use it.