Even new trains are hard on the ears. Credit: © Punchstock images

High-speed trains gliding along with magnetic levitation look as if they should be sleek and silent. But not so, according to a new study.

Magnetically levitated (maglev) trains might cause more noise pollution than today's intercity trains, according to a report by Joos Vos of the Dutch research institute TNO Human Factors, Soesterberg, in the Journal of the Acoustical Society of America1.

Vos played people recordings of maglev and normal trains that mimicked the sound levels in houses near railway lines. When asked how annoying they would find the sound if regularly exposed to it at home, participants rated the maglev noise as more disturbing than standard intercity trains.

Strong magnetic fields suspend maglev trains a few centimetres above their tracks; electromagnetic forces between train and track propel them. The reduced friction allows maglevs to run at about twice the speed of current intercity trains.

Train or plane?

Prototype maglev trains have been tested in Japan, Germany and China. The first commercial line, built by German company Transrapid, opened between Shanghai, China, and the city's Pudong Airport in 2003, and has clocked a record speed of 500 kilometres per hour. In the United States, projects are planned for Pittsburgh and Baltimore.

But the future of such trains may depend in part on their environmental impact. Previous studies have shown that maglev and intercity trains can be equally loud. But noise-pollution depends on the quality of the noise as well as its volume.

At high speeds, says Vos, "the maglev sound is similar to that of some aircraft".

Vos's subjects found the maglev and road noise equally annoying, and considered both worse than intercity trains. Many said that the maglev noise made them feel insecure, some found it startling, and disliked the occasional shrill sound the maglevs produced.

Vos thinks part of the problem might simply be unfamiliarity with the noise. As people get used to it, he says, they might find it less annoying. And, he adds, quieter maglev trains may be built in the future.