I'm aware the big rail companies are looking at liquefied natural gas because they can carry a tank of it behind the locomotive. It's more efficient for them to carry their fuel that way than it is to carry a tank of urea, which is what they have to do to scrub the particulates out of their exhaust to meet tier-four standards. So there's a big struggle happening. Some of them are actually going to use the urea systems, but I understand there are some discussions going on with CN about creating a fleet of natural-gas-powered vehicles that--and correct if I'm wrong--could actually go across Canada twice on one tank.
On May 17th, 2012. See this statement in context.