🌊 New Guideline to Stop Underpass Flooding Accidents

❓ What's changing?

On 6 October 2026, Japan's Ministry of Land, Infrastructure, Transport and Tourism (MLIT) issued the "Guideline for Preventing Flooding Accidents at Underpasses." An underpass is a dipped section of road that runs beneath a railway or another road. Because it sits lower than the surrounding ground, heavy rain can pour in and flood it deeply within minutes, trapping vehicles that have already entered. The guideline follows the August 2026 Chiba torrential rain, in which underpass flooding caused injuries and property damage, and similar damage has continued to occur elsewhere during heavy rain. On 27 August 2026 MLIT set out "interim measures" and road managers began with the steps that could be implemented immediately. The new guideline organizes those efforts systematically, setting out the basic approach to traffic restrictions and vehicle-entry prevention according to each site's flooding risk. The key shift is that flood prevention no longer relies on drainage equipment alone. The guideline combines three elements into "multi-layered defense": (1) preventive closure before water arrives, plus prompt closure once flooding occurs; (2) measures that reliably stop vehicles from entering while a closure is in force; and (3) securing drainage capacity. It also adopts a "fail-safe" principle so that systems shift to the safe side when something goes wrong. Measures cover both equipment and day-to-day operation, tailored to each location. The full text is published on the MLIT Road Bureau website.

👥 Who is affected?

• ●Anyone driving or riding through an underpass on a rainy day, including everyday commuting, shopping, and school runs
• ●Travelers using rental cars or car sharing, who may not know which stretches of road sit in a dip
• ●People who cross underpasses on foot or by bicycle, since some have sidewalks
• ●Anyone planning a long drive when a typhoon or a linear rainband is approaching
• ●Drivers whose job means repeating the same route daily, such as delivery or sales

🌏 Impact on foreign residents and visitors

For foreign residents and visitors, the biggest practical change is that roads may be closed while the pavement still looks dry. Because the guideline puts preventive closure — before flooding actually occurs — at the center, you may meet a barrier at a perfectly passable-looking underpass. If you cannot read Japanese signs such as 通行止 (road closed) or 冠水のため通行止 (closed due to flooding), or do not recognize what a gate or barricade means, it is easy to assume you can still get through and lose time deciding on a detour. If you live in Japan, check on a clear day whether the route you use daily — commuting, the nursery run — passes through an underpass, and decide on an alternative route in advance. That way a closure on a rainy morning does not leave you stranded. Travelers should note that a rental car's navigation may route you through a low-lying underpass simply because it is the shortest path; on days with a heavy rain warning, choosing a main arterial road instead is a sound call. In every case, the rule is simple: do not enter a closed underpass — turn back. The guideline calls for measures that reliably keep vehicles out, and driving around a barricade is not an option it contemplates.