Diesel now has a dim future at best among U.S. passenger-car buyers, though its prospects continue to look strong for a minority of pickup truck buyers.

Heavy-duty commercial vehicles, on the other hand, largely use diesel engines as a matter of course.

We asked our Twitter followers when that would end—specifically, when the very last diesel truck would be sold in the U.S.

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Unlike our polls on electric-car issues, which often skew predominantly toward a single respose, the range of opinions on this one was quite distributed.

The most common answer of our four options, chosen by 37 percent of respondents, was that the last diesel truck would be sold in 2030.

But the next most common, chosen by just over a quarter (26 percent), was "Never."

The other two choices, 2020 and 2050, were picked by almost even percentages of respondents: 19 and 18 percent, respectively.

So while our followers seem to expect the prospects for diesel to decline over the coming decades, there's little consensus on how fast that will happen.

ALSO SEE: EPA releases final heavy-truck emissions rules

The EPA has just issued final rules for a second set of fuel-economy regulations for heavy trucks, to take effect from 2021 through 2027.

Those will clearly spur efforts to boost efficiency via better aerodynamics, more efficient powertrains, and more.

Nikola One electric semi truck

Nikola One electric semi truck

But the energy density of hydrocarbon fuels matters much more for vehicles weighing 15,000 to 50,000 pounds than it does for passenger vehicles of 2,500 to 6,000 pounds.

And some suggest that compressed or liquid natural gas, or hydrogen, may be the only medium-term solution for the heaviest and longest-range road vehicles.

CHECK OUT: Nikola One 2000-hp natural gas-electric semi truck announced

How that plays out remains to be seen, and consideration of those questions may be somewhere behind that for far more numerous passenger vehicles.

But given the gigantic amounts of diesel fuel consumed—and carbon emitted—by very heavy vehicles that travel huge distances with very low fuel efficiency, it's a matter of great consequence.


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