The companies that build those vehicles are eyeing the technology but also keeping a view of how regulations might develop for clean transportation.
"We are continuing to invest in the combustion engine, and we are looking to see if we can use hydrogen in that application as well," said Jessica Sandström, senior vice president, global product management at Volvo Trucks.
"One of the uncertainties, of course, is the political decisions regarding zero emission," Sandström said. "Is it zero CO2 or is it zero emission, full stop? If you have a combustion engine, even with hydrogen, you will get very small emissions coming out, nitrogen oxide."
Daimler Truck Group's Detroit family of diesel engines can run on hydrogen, said Martin Daum, Daimler Truck CEO.
"If we see a market coming, we can pull it off the pre-development stage and put it into a full-fledged project," Daum told Automotive News.
The truck company is waiting "because all the signals from regulators in Europe and California are to ban combustion entirely," Daum said.
But there's likely to be room in the market for hydrogen combustion engines somewhere, and their compatibility with diesel engines is an advantage, said Daniel Sperling, founding director of the University of California, Davis, Institute of Transportation Studies and a member of the California Air Resources Board.
"Just because Europe and California want something, that doesn't mean that's the whole market," Sperling said.
Still, he's skeptical the industry will deploy hydrogen combustion widely.
"A fuel cell is much more efficient than combustion. You use less energy. You then don't have the cost of expensive tanks on the vehicle. You don't have the NOx emissions," Sperling said.
"No one knows how this will play out, and we are all trying to figure it out."