Image: https://www.pib.gov.in/ Diesel trains have been rattling down tracks for so long that most of us stopped thinking about what comes out of their exhaust. Now there's a quieter alternative showing up on a handful of railway lines around the world, one that runs on hydrogen instead of diesel and leaves behind nothing but water vapour. With India rolling out its first hydrogen train, the question a lot of people are suddenly asking is a fair one: how many countries actually have these things?Given how much buzz hydrogen gets as the fuel of the future, you'd think half the world…