Researchers believe they may have solved the “tunnel boom” issue as China prepares to introduce its newest magnetic levitation train prototype.
The latest maglev train can reach speeds of 600 km/h (about 370 mph), but engineers have struggled with shock waves that occur when the train exits a tunnel. When a high-speed train enters a tunnel, it compresses the air in front like a piston, creating pressure fluctuations that merge at the tunnel exit, producing low-frequency shock waves—similar to, but distinct from, the sonic boom of supersonic aircraft. These shock waves can disturb nearby people and animals, damage structures, and pose safety risks.
Now, researchers have found that installing specially designed soundproof buffers at tunnel entrances can reduce these shock waves by up to 96%. This breakthrough improves operational safety, reduces noise pollution, enhances passenger comfort, and protects wildlife near future rail lines.
While conventional high-speed trains (which reach up to 350 km/h or 217 mph) also face this issue, the problem worsens at higher speeds. Shock waves grow stronger, and the tunnel length needed to trigger a boom shortens dramatically. For example, a 600 km/h train creates a boom in tunnels as short as 2 km (1.2 miles), whereas conventional trains only produce booms in tunnels 6 km or longer.
The new 100-meter-long buffers, made with a porous structure and combined with porous tunnel coatings, allow trapped air to escape before the train exits, suppressing the boom much like a firearm silencer.
Maglev trains use magnetic forces to float above the track, eliminating friction and allowing much higher speeds than conventional trains. There are two main systems:
– Electromagnetic Suspension (EMS): The train wraps around a steel rail, with electromagnets lifting it slightly (about 10 mm) through attraction.
– Electrodynamic Suspension (EDS): The train hovers inside a U-shaped guideway, using superconducting coils to create a mix of repelling and attracting forces for levitation.
China first introduced high-speed maglev trains in 2004, with a line between Shanghai’s Pudong Airport and the city outskirts reaching 460 km/h (286 mph)—still the fastest commercial rail service in operation. However, development later shifted to conventional high-speed rail, which now spans 48,000 km (30,000 miles), the world’s largest network.
Now, state-owned manufacturer CRRC is reviving maglev technology with a new model launched in 2021. Passengers report an exceptionally smooth and quiet ride, with only the faint hum of electromagnets—no mechanical noise.Weekly Newsletter
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While no official routes have been finalized, experts anticipate a future high-speed rail line connecting Beijing and Shanghai. This would cut travel time from 4.5 hours to just 2.5 hours—roughly the same as a domestic flight between the two cities.
In China, high-speed rail tickets are more affordable than air travel (¥600 vs. ¥1,200), unlike in many other countries. Trains also produce about seven times less CO2 per kilometer than planes, offering significant environmental benefits.
China isn’t alone in developing long-distance maglev trains. Japan is also advancing its Chuo Shinkansen project, which will connect Tokyo and Osaka via Nagoya at speeds of 505 km/h (314 mph). The current high-speed rail takes 2.5 hours, but the maglev could slash that to just 67 minutes. Originally set for partial operation in 2027, delays have pushed the timeline back, with no confirmed opening date yet.
