The U.K.’s rail sector is working to fast-track hydrogen-powered trains after policymakers lent their support to the idea in recent weeks.

Reports last month said the U.K. Rail Safety and Standards Board, working with train maker Alstom, is hoping to start a hydrogen-powered train pilot by 2019 or early 2020.

The moves come after U.K. Transport Secretary Chris Grayling said hydrogen trains were “a priority,” and Transport Minister Jo Johnson signaled the government would consider taking diesel locomotives off the rails altogether by 2040.

The decision to introduce hydrogen trains into the U.K. rail network came after the government opted not to electrify the northern part of the Midland Main Line, a major rail route connecting London with Manchester and Leeds.

Pressed on the environmental consequences of canceling the electrification project, Grayling told members of Parliament in January that he wanted hydrogen trains to begin operating on the rail network “within a short period” of time.

“I expect to see a transformation of technology on our railways over the coming years, with the introduction of different types of battery electric hybrid trains and hydrogen trains, and I see that as a priority,” he said.

In a speech last month, Johnson confirmed the government was looking at hydrogen after having dismissed full-scale electrification of the rail network. “Alternative-fuel trains powered entirely by hydrogen are a prize on the horizon,” he declared.

“I’d like to see hydrogen train trials on the U.K. railway as soon as possible. Hydrogen offers an affordable -- and potentially much cleaner -- alternative to diesel. And the technology has developed [rapidly] in recent years.”

Johnson cited Alstom and Rolls-Royce as two companies commercializing hydrogen rail, or "hydrail," technology. Of the two, Alstom seems the most advanced, with a commercially available hydrail called the Coradia iLint.

The train, which can carry up to 300 passengers, has a top speed of 87 miles per hour and a range of almost 500 miles. Alstom launched the Coradia iLint in September 2016 and began testing it in Germany and the Czech Republic in March of last year.

The tests put Germany at the forefront of hydrail development, but interest in hydrogen-based rail transport has also been increasing elsewhere. Canada, for example, has been looking into the use of hydrogen fuel cells to power trains on the Ontario Metrolinx network.

A feasibility study by Metrolinx concluded the overall lifetime costs of building and operating a hydrail system would be the same as opting for overhead electrification. The rail authority is planning to bring in hydrail by 2025.

However, it noted: “The implementation of the hydrail system of this scale and complexity has never been undertaken, and presents a different set of risks as compared to conventional electrification.”

Current interest in hydrail systems follows more than a decade of technology development.

The East Japan Railway Company developed a hydrail hybrid in 2006, and the U.S. Army Corps of Engineers plus BNSF and Vehicle Projects unveiled the first hydrogen-powered locomotive in 2010. China and South Africa have also hosted fuel-cell locomotive projects.

Even in the U.K., the idea of hydrogen-based trains is not new. The University of Birmingham created a hydrogen-powered locomotive in 2012; although with a total output of 4.4 kilowatts it was hardly fit to carry commuters.

Despite advances in the technology, there are still lingering doubts over the use of hydrogen for rail transport, including how much it will cost.

U.K. expert Stephen Kent, a teaching fellow at the Birmingham Center for Railway Research and Education, said “the day-to-day maintenance is almost certainly cheaper than for a comparable diesel engine.”

But the cost of fuel, he said, depends to a large degree on how much you pay per kilowatt-hour for electricity or natural gas. “If you get your electricity for free, which isn't out of the question, then generating hydrogen will almost certainly be cheaper than diesel,” he said.

“If you pay full [price] for your electricity, then this isn't necessarily going to be the case.”