Varje morgon vid en transitanläggning i Canton, Ohio, kör mer än ett dussin bussar upp till en tankstation innan de fläktar ut till sina rutter i denna stad söder om Cleveland.

Bussarna – tillverkade av El Dorado National och ägda av Stark Area Regional Transit Authority – ser ut som alla andra. Men tillsammans återspeglar de framkanten av en teknik som kan spela en nyckelroll för att producera renare transporter mellan städer. I stället för föroreningar som rapar diesel, kör en fjärdedel av myndighetens bussar på vätgas. De avger inget annat än ofarlig vattenånga.

Väte, det vanligaste grundämnet i universum, ses i allt högre grad, tillsammans med elfordon, som ett sätt att bromsa den miljöförstörande påverkan av planetens 1,2 miljarder fordon, varav de flesta förbränner bensin och diesel. Tillverkare av stora lastbilar och kommersiella fordon börjar anamma vätebränslecellsteknik som en väg framåt. Det är också tillverkare av flygplan, tåg och passagerarfordon.

Transporter är USA:s enskilt största bidragsgivare till klimatförändringarna, varför vätekraft i det långa loppet ses som ett potentiellt viktigt sätt att hjälpa till att minska koldioxidutsläppen.

För att vara säker, förblir väte långt ifrån en magisk lösning. För närvarande tillverkas det väte som produceras globalt varje år, främst för raffinaderier och gödseltillverkning, med naturgas eller kol. Den processen förorenar luften, värmer upp planeten snarare än att rädda den. Faktum är att en ny studie av forskare från Cornell- och Stanford-universitetet fann att den mesta väteproduktionen släpper ut koldioxid, vilket innebär att vätgasdrivna transporter ännu inte kan betraktas som ren energi.

Ändå säger förespråkare för vätgasdrivna transporter att på lång sikt är vätgasproduktion avsedd att bli mer miljövänlig. De föreställer sig en växande användning av el från vind- och solenergi, som kan separera väte och syre i vatten. Eftersom sådana förnybara energiformer får bredare användning bör väteproduktion bli en renare och billigare process.

Inom tre år planerar General Motors, Navistar och lastbilsföretaget J.B. Hunt att bygga bensinstationer och köra vätgasbilar på flera amerikanska motorvägar. Toyota, Kenworth och Los Angeles hamn har börjat testa vätgasbilar för att transportera varor från fartyg till lager.

Volvo Trucks, Daimler Trucks AG och andra tillverkare har också tillkännagett partnerskap. Företagen hoppas kunna kommersialisera sin forskning och erbjuda nollutsläppslastbilar som sparar pengar och uppfyller strängare föroreningsbestämmelser.

I Tyskland började ett vätgasdrivet tåg trafikera 2018, och fler kommer. Franska Airbus, världens största tillverkare av flygplan, överväger också vätgas.

"Det här är ungefär det närmaste jag har sett oss komma hittills den verkliga vändpunkten", säger Shawn Litster, professor i maskinteknik vid Carnegie Mellon University som har studerat vätebränsleceller i nästan två decennier.

Väte har länge varit ett råmaterial för produktion av gödningsmedel, stål, petroleum, betong och kemikalier. Det har också kört fordon i flera år:Cirka 35 000 gaffeltruckar i USA, cirka 4% av landets totala, drivs av vätgas. Its eventual use on roadways, to haul heavy loads of cargo, could begin to replace diesel-burning polluters.

No one knows when, or even whether, hydrogen will be adopted for widespread use. Craig Scott, Toyota's head of advanced technology in North America, says the company is perhaps two years from having a hydrogen truck ready for sale. Building more fueling stations will be crucial to widespread adoption.

Kirt Conrad, CEO of Canton's transit authority since 2009, says other transit systems have shown so much interest in the technology that SARTA takes its buses around the country for demonstrations. Canton's system, which bought its first three hydrogen buses in 2016, has since added 11. It's also built a fueling station. Two California transit systems, in Oakland and Riverside County, have hydrogen buses in their fleets.

"We've demonstrated that our buses are reliable and cost-efficient, and as a result, we're breaking down barriers that have slowed wider adoption of the technology," Conrad said.

The test at the Port of Los Angeles started in April, when the first of five semis with Toyota hydrogen powertrains began hauling freight to warehouses in Ontario, California, about 60 miles away. The $82.5 million public-private project eventually will have 10 semis.

Hydrogen fuel is included in President Joe Biden's plans to cut emissions in half by 2030. The infrastructure bill the Senate approved passed this week includes $9 billion for research to reduce the cost of making clean hydrogen, and for regional hydrogen manufacturing hubs.

The long-haul trucking industry appears to be the best bet for early adoption of hydrogen. Fuel cells, which convert hydrogen gas into electricity, provide a longer range than battery-electric trucks, fare better in cold weather and can be refueled much faster than electric batteries can be recharged. Proponents say the short refueling time for hydrogen vehicles gives them an edge over electric vehicles for use in taxis or delivery trucks, which are in constant use.

That advantage was important for London-based Green Tomato Cars, which uses 60 hydrogen fuel cell-powered Toyota Mirai cars in its 500-car zero emission fleet to transport corporate customers. Co-founder Jonny Goldstone said his drivers can travel over 300 miles (500 kilometers) on a tank and refuel in three minutes.

Because drivers' earnings depend on fares, Goldstone said, "if they have to spend 40, 50 minutes, an hour, two hours plugging a car in in in the middle of the working day, that for them is just not acceptable."

For now, Green Tomato is among the largest operators of hydrogen vehicles in what is still a tiny market in Europe, with about 2,000 fuel cell cars, garbage trucks and delivery vans on the roads.

About 7,500 hydrogen fuel cell cars are on the road in the U.S., mostly in California. Toyota, Honda and Hyundai produce the cars, which are priced thousands more than gasoline-powered vehicles. California has 45 public fueling stations, with more planned or under construction.

Unlike with buses and heavy trucks, experts say the future of passenger vehicles in the U.S. lies mainly with electric battery power, not hydrogen. Fully electric vehicles can travel farther than most people need to go on a relatively small battery.

And for now, hydrogen production is adding to rather than reducing pollution. The world produces about 75 million tons a year, most of it in a carbon emission-creating processes involving steam reformation of natural gas. China uses higher-polluting coal.

So-called "blue" hydrogen, made from natural gas, requires an additional step. Carbon dioxide emitted in the process is sent below the earth's surface for storage. The Cornell and Stanford study found that manufacturing blue hydrogen emitted 20% more carbon than burning natural gas or coal for heat.

That's why industry researchers are focused on electrolysis, which uses electricity to separate hydrogen and oxygen in water. Hydrogen mixes with oxygen in a vehicle's fuel cell to produce power. The amount of electricity generated by wind and solar is growing worldwide, making electrolysis cleaner and cheaper, said Joe Cargnelli, director of hydrogen technologies for Cummins, which makes electrolyzers and fuel cell power systems.

Currently, it costs more to make a hydrogen truck and produce the fuel than to put a diesel-powered truck on the road. Hydrogen costs about $13 per kilogram in California, and 1 kilogram can deliver slightly more energy than a gallon of diesel fuel. By contrast, diesel fuel is only about $3.25 per gallon in the U.S.

But experts say that disparity will narrow.

"As they scale up the technology for production, the hydrogen should come down," said Carnegie Mellon's Litster.

While a diesel semi can cost around $150,000 depending on how it's equipped, it's unclear how much fuel cell trucks would cost. Nikola, a startup electric and hydrogen fuel cell truck maker, estimated last year that it would receive about $235,000 for each hydrogen semi it sells.

Clean electricity might eventually be used to make and store hydrogen at a rail yard, where it could refuel locomotives and semis, all with zero emissions.

Cummins foresees the widespread use of hydrogen in the U.S. by 2030, sped by stricter diesel emissions regulations and government zero-emissions vehicle requirements. Already, Europe has set ambitious green hydrogen targets designed to accelerate its use.

"That's just going to blow the market open and kind of drive it," Cargnelli said. "Then you'll see other places like North America kind of follow suit."