Economy Samyak IAS 18 Jun, 2026 2 min read

Tunnel Hood Technology

Bullet train tunnel ‘hoods’: What they are and why they matter-INDIAN EXPRESS

The tunnel hood technology for India’s Mumbai–Ahmedabad High Speed Rail (MAHSR) bullet train project has been designed and implemented for railway tunnels in India for the first time. The tunnels in the project will have hoods at both entry and exit points to reduce pressure effects created by high-speed trains.

1. What are Tunnel Hoods?

Tunnel hoods are cylindrical perforated structures built at the entrance and exit of railway tunnels.
They act as pressure-relief vents or windows.
They help reduce the tunnel boom effect caused by pressure waves generated by high-speed trains.

2. Need for Tunnel Hoods

High-speed trains, especially those running above 300 kmph, push a large volume of air into tunnels.
Sudden compression of air creates pressure waves.
If not managed, these pressure waves can cause a booming noise when the train exits the tunnel.
Tunnel hoods ensure smoother entry and exit by controlling sudden air pressure buildup.

3. How Tunnel Hood Technology Works

At the entry point, air escapes through perforated hood openings.
Inside the tunnel, the pressure wave becomes weaker.
At the exit point, the train exits more quietly because the pressure is already reduced.
This improves aerodynamic performance and passenger comfort.

4. Use in MAHSR Project

The 508-km Mumbai–Ahmedabad High Speed Rail project has seven mountain tunnels in Maharashtra and one mountain tunnel in Gujarat.
Each tunnel will have hoods at both entry and exit points.
Gujarat’s only tunnel in Valsad is near completion.

5. Tunnel Hood Windows

The hood windows help release air pressure gradually.
In Palghar, seven tunnels will have hood windows ranging from 20 to 26.
Each window size ranges from 31 metres to 45 metres on each side.
This increases the overall length of the tunnel.

6. Key Example: Tunnel T-6

Tunnel T-6 in Palghar was originally 390 metres long.
Due to hood windows, the total length increased to 454 metres.
Work began on January 31, 2025.
Breakthrough was achieved in 360 days.

7. Engineering Significance

Hoods are crucial in tunnels passing through difficult mountain regions like the Sahyadri mountains.
They reduce noise, improve safety and support smooth high-speed train operation.
The technology marks an upgrade in India’s tunnel construction system.