Argentina advances project to turn diesel locomotives to natural gas
Locomotives, as well as vessels, are ideal conversion objects to LNG. LNG needs a little bigger tank than diesel does and the bigger those devices are, the less the bigger tank is an issue. And diesel rail corridors in cities are the areas with the worst air pollution. LNG will clean that up in a second. Plus, if you have indigenous gas, you can use that (or biogas) instead of imported oil. Little side benefit: trains could form the best line pack gas supply a city has.
NGV Journal 
