Locomotives have relied on diesel engines as their primary propulsion system since the Second World War, but the recent explosion of liquid natural gas availability may nudge railroad companies away from the status quo.
The Christian Science Monitor explained that major railroad companies like CSX, Union Pacific, BNSF, and Canadian National are keen to explore alternative fuels for their trains due to the immense cost of diesel. General Electric and Caterpillar, the two biggest manufacturers of train engines, are in the process of vetting liquid natural gas and LNG/diesel hybrid powerplants that they hope will someday be the standard in railroad freight transportation.
Hydraulic fracturing (fracking) has recently boosted the hell out of the natural gas supply, and dropped the price to less than a third of their peak in 2008. Fracking involves blasting open cracks in underground rocks with high-pressure liquid to extract oil or gas. While there are definitely those who oppose the damage it renders to the planet, it's no doubt it's yielding juice. "Only 3%" of vehicles in the US currently use LNG now, but if price continues to plummet it will assuredly have fleet operator's attention.
Full-on conversions for trains to LNG would be complex; the train application requires the fuel to be cooled to -260 ºF and railroad executives estimate the cost will be about $2 million per engine. But some kind of hybrid system where diesel fuel begins the combustion process and provides supplementary power is being considered that could reduce initial spending and expedite the adoption of the new fuel.
If it does happen, it'll be a long-game kind of change. There are some 140,000 miles of railroad tracks devoted to freight transport and all the support systems along the way are currently designed around diesel power. Engineers from CSX and Union Pacific told the Monitor "it's too early" to truly understand the costs and benefits of a move to LNG, but of course they're eager to explore anything that will make their operations cheaper to run.