Guidelines to Prevent Underpass Flooding Accidents
Overview
In response to more frequent and severe heavy rainfall associated with climate change and other factors, and to personal injury and property damage caused by flooded underpasses in various regions, including incidents after the August 2026 Chiba heavy rain, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) has established the Guidelines for Preventing Flooding Accidents at Underpasses. The guidelines set out basic principles for measures such as traffic restrictions based on flood risk and preventing vehicles from entering, and call for action on both equipment and operational fronts.
Key points
- Combine preventive traffic restrictions in advance, prompt restrictions when flooding occurs, measures to prevent vehicles from entering, and measures to maintain drainage capacity.
- Establish a fail-safe approach that shifts to a safer state even when an abnormal event occurs.
- Flooding caused personal injury and property damage during the August 2026 Chiba heavy rain and other events.
Overview
In light of more frequent and severe heavy rainfall associated with climate change and other factors, guidelines have been established to organize concrete measures to prevent flooding accidents at underpasses. Flooding caused personal injury and property damage during the August 2026 Chiba heavy rain, and similar damage has occurred in various regions since then.
Initial measures were announced on August 27, 2026, and work has proceeded promptly, starting with measures that could be implemented.
Impact
The guidelines aim to ensure the safety of road users.
Details
The guidelines systematically organize basic principles for measures such as traffic restrictions based on flood risk and preventing vehicles from entering. They are based on multiple layers of protection and a fail-safe approach that shifts to a safer state even when an abnormal event occurs.
Effective measures will be implemented according to conditions at each location, addressing both equipment and operations. An outline is provided in an accompanying document, and the full text is available on the Road Bureau website.