Once all 14 of the new trains are in service, the line will become the first route to run exclusively on hydrogen, according to a statement from Alstom, the France-based company that developed the trains.

The high-tech trains, called Coradia iLint, combine hydrogen with oxygen to produce power. The byproducts are only steam and water, and any heat created gets recycled and used to power the trains' air conditioning systems.

Diesel trains, on the other hand, produce high amounts of nitrogen dioxide pollution--even more so than cars traveling on busy streets, according to a study published last year. Developers say the new hydrogen trains are quiet, and they make the air cleaner for passengers to breathe.

"It's less noisy," says Bruno Marguet, an executive with Alstom, to Fast Company's Adele Peters. "You don't smell the diesel smoke when you're in the station... there aren't diesel emissions from [nitrogen oxides], which are harmful for health."