Stephen Richards wrote:
Caught one of the new emission free busses on the 25 today. I thought
they were electric, and expected them to sound the same as a trolleybus;
but they sound just like a very quiet diesel engine, with very definite
gear changes. Can anyone explain what technology is used?

Hydrogen fuel cells. Although they're labelled emission free,
technically water is their sole emission.

http://www.tfl.gov.uk/buses/fuel-cell-buses.shtml

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Dave Arquati
Imperial College, SW7
www.alwaystouchout.com - Transport projects in London