Railroads are experimenting with liquefied natural-gas locomotivesFreight rail is a very efficient way to move goods over long distances, moving a ton of freight around 500 miles on a single gallon of diesel. But railroads still burn around 3.1 billion gallons of diesel a year just in the US, and are behind only the U.S. Navy when it comes to diesel consumption. What if a less carbon-intensive and less air-polluting source of fuel could be used? The BNSF (the second largest railroad in the US), the CN in Canada, and probably other railroads, have been experimenting with natural gas locomotives. Matt Rose, the CEO of BNSF, even thinks that a transition to natural gas could be as big a revolution for his industry as the switch away from steam locomotives was.
Ideally, freight rail would be electrified, like a lot of passenger rail. But running power lines over 32,000+ miles of tracks (that's just the BNSF) isn't exactly a small project. Maybe when batteries and/or hypercapacitors are good enough, freight rail could be electrified by using fully electric locomotive (maybe with a car of batteries being towed behind), but we're not quite there yet either.
So in the meantime, natural gas might be an improvement over diesel. It's certainly not perfect, as it is a fossil fuel that produces greenhouse gases. But compared to diesel, it seems a step up if the railroads tap into all that natural gas that is just being flared (ie. stupidly wasted) around North-Dakota and other oil-producing regions.
It's incredibly stupid to just burn up all that non-renewable energy without getting anything out of it, so we might as well run the country's railroads on it. And it just so happens that BNSF has a lot of tracks going in that area, so they could build facilities to liquify that natural gas and run their first LNG-powered locomotives from there.
But big gains in CO2 reductions would only be made if flared gas is primarily used. If not, we would still see pretty big gains when it comes to smog-forming emissions, but the carbon intensity of diesel vs. liquefied natural gas is not hugely different. From a green point of view, this is an opportunity to deal with the flaring problem.