We will likely never see battery-electric trucks enter the long-haul freight mainstream, but other alternatives to diesel fuel exist today.
One is natural gas, which comes with fewer packaging and range constraints than electric propulsion--and a ready and growing domestic supply of the fuel.
So why aren't natural gas-powered trucks selling better?
It's all about another kind of green: money
Natural-gas trucks just don't make financial sense for many fleet operators, according to a new report from The Wall Street Journal (subscription required).
First, a natural-gas vehicle carries an average $50,000 premium over a typical heavy-duty diesel truck, which usually costs about $150,000.
In theory, that extra money spent on purchasing the truck could be offset by fuel savings of $1.60 and $1.70 per gallon for the amount of natural gas with an energy content equivalent of 1 gallon of diesel.
Natural Gas-powered Kenworth truck (Image: Flickr user TruckPR)
But that is roughly the average lifespan of a truck in a big fleet--meaning it will likely be replaced before the operator sees any real financial benefit.
Compressed natural gas also contains 20 percent less energy by volume than an equal amount of diesel, so drivers have to fill up more often if the tanks take up the same space.
That's sometimes easier said than done, as there are only about 1,500 natural-gas fueling stations in the U.S. Of that total, just slightly more than half are open to the public--and many cannot accommodate a large truck.
Customers also expect any fuel savings to be passed on to them in the form of lower rates, so that money often can't be applied to equipment costs.
At the same time, diesel engines are getting more efficient.
Federal regulations require a 6-percent improvement in fuel economy for big trucks by 2017. The first phase of the new rules takes effect this year, and will see average fuel economy for new trucks increase to 7 mpg from 6.5 mpg.
President Barack Obama has asked the EPA to follow up with a new set of standards that will further increase efficiency between 2018 and 2025.
Despite the drawbacks, natural-gas truck sales are expected to increase by 20 percent this year, to 10,480 units.
However, that's less than 4 percent of the 281,620 diesel trucks that analysts project will be sold in North America this year.