Rail carriers contemplate life after diesel: What’s next?

The freight-rail industry is facing pressure to find cleaner alternatives to its traditional diesel-electric locomotives.
The freight-rail industry is facing pressure to find cleaner alternatives to its traditional diesel-electric locomotives.


Rail carriers are under pressure to lower greenhouse-gas emissions. Here are some of the alternative technologies they are considering.

Railroad operators like to say that trains are greener than trucks when it comes to moving goods, pointing out that one railcar can haul three to four times as much as a truck, and one freight train can remove hundreds of trucks from the highways.

Although the freight-rail industry is responsible for less than 2% of transportation-related greenhouse-gas emissions in the U.S., rail carriers—like the rest of the transportation industry—are under pressure to reduce those emissions, much of which are produced by diesel-electric locomotives.

As a result, freight operators are investing in diesel-electric models that are more fuel-efficient, as well as exploring alternative ways to power locomotives, homing in on three main technologies: batteries, biodiesel and hydrogen.

Coming up with cleaner alternatives to diesel-powered locomotives isn’t easy. Any alternative would need to be able to haul freight across mountainous and desert regions, in various weather conditions and temperatures. That, combined with the complexities involved in building new refueling infrastructure for alternative fuels and uncertainty over access to constrained supplies, make it unlikely that zero-emission locomotives will be widespread by the mid-2030s as called for in the U.S. National Blueprint for Transportation Decarbonization, the industry says.

“At this point, there is no clear winner in the next-generation locomotive fight," says Bascome Majors, an analyst at Susquehanna International Group.

Here is a closer look at some of the new technologies being tested by rail carriers.

Battery power

Battery-electric locomotives are one emissions-reducing option but their battery-storage capacity, and therefore their range, limit how they can be used—at least for now.

Major freight railroads are using or plan to use battery locomotives in some of their port-unloading and rail-yard operations. Some short-line railroads are testing them, too. But with energy capacity of around 2.4 to 2.7 megawatt-hours, these locomotives have far less range than a 5,000-gallon diesel locomotive, which has roughly 76 megawatt-hours of energy.

This year, rail-equipment and technology provider Wabtec plans to deliver locomotives with battery capacity ranging from 7 to 8 megawatt-hours that it says can be added onto freight trains that make long-haul runs. Longer freight trains are often powered by multiple locomotives, so the idea is to add a battery-powered model into the mix to reduce fuel consumption. This is what is known as a hybrid “consist."

“With battery technology in locomotives, it’s ‘and’ rather than ‘or,’ " says Eric Gebhardt, chief technology officer of Pittsburgh-based Wabtec.

Still, research and testing focused on increasing battery capacity is continuing. One feature being tested is regenerative braking, which captures kinetic energy when a train decelerates or goes downhill and converts it into electrical energy that can be stored in the battery. In 2021, a Wabtec FLXdrive battery locomotive on a test run in California was able to recharge itself three times in a 27-hour window, according to Gebhardt.

Another hurdle facing battery locomotives is how long it takes to charge them. “Diesel locomotives can be fueled in 20-30 minutes today, compared to several hours of charging time, which affects operational viability," says a spokeswoman for Berkshire Hathaway-owned BNSF Railway in Fort Worth, Texas, which is testing battery locomotives in freight transportation and yard operations.

Some smaller rail operators also have reservations about the reliability of battery locomotives, especially in freezing temperatures.

“If we were to electrify all of our locomotives and then we have a disruption in the charging or we have a charger that goes down, then we are absolutely out of service," says Justin Thompson, chief executive of Iron Senergy, a Waynesburg, Pa.-based energy company that has three locomotives transporting coal across 17 miles of track. The company instead is testing battery-powered railcars, which can be added to a freight train for supplemental power.


In recent years, major rail carriers including Union Pacific, BNSF, Norfolk Southern, Canadian National Railway and Canadian Pacific Kansas City, or CPKC, have tested or started using various blends of biodiesel and renewable diesel. Wabtec, which also modifies locomotives so they can burn both alternative fuels and regular diesel, has said this option has the potential to reduce carriers’ carbon emissions by as much as 60%.

Biodiesel and renewable diesel are fuels made from fats and oils such as soybean oil, though they are produced by different processes.

Modifying the engines of current locomotives to enable them to burn biodiesel and renewable diesel is currently the fastest way for railroads to lower their emissions, experts say. Biofuels are the low-hanging fruit for railroads in terms of what will be the least disruptive to rail carriers’ existing operations, says Kari Gonzales, president at rail research firm MxV Rail.

Such modifications also are appealing because the locomotives can still operate using regular diesel if the supply of biodiesel or renewable diesel is constrained, railroad operators and shippers say.

Still, biodiesel presents challenges.

The supply of alternative fuels is unreliable compared with regular diesel because of limited feedstock and a patchwork of state subsidies, say railroad executives. What’s more, demand for sustainable aviation fuel from the airline industry, which has fewer decarbonization options compared with other transportation sectors, has led to shortages of biodiesel for the rail industry, they say.

The Association of American Railroads, an industry trade group, has called for the imbalances in the market to be addressed, telling Energy Department officials this year that “federal and state policies should harness market principles to encourage the development and equitable deployment of low-carbon fuels for use in all modes of transport."

Hydrogen fuel cells

At least two freight railroads in North America, Canadian Pacific Kansas City and CSX, are testing hydrogen fuel-cell locomotives. With this technology, hydrogen gas is fed into the fuel cell to generate electricity, which powers the locomotive’s motors.

Hydrogen fuel-cell locomotives emit only water vapor and they have more energy capacity than battery locomotives, though not as much as diesel locomotives. Refueling via liquefied tankers takes only around 45 minutes, eliminating the hurdle of having to wait hours for a battery to recharge or to build dedicated substations in terminals for charging. This addresses network interoperability, a key issue for freight railroads because trains sometimes travel on other operators’ tracks, or head to destinations that lack infrastructure and access to alternative fuels.

Since 2020, CPKC has retrofitted three locomotives with hydrogen fuel cells to test within its network. One was able to haul 25,000 tons of freight through a mountainous territory, says Kyle Mulligan, assistant vice president of operations technology at the carrier, indicating that the hydrogen locomotive has the same propulsion power as diesel locomotives in terms of hauling freight in uphill conditions.

CSX, meanwhile, has retrofitted one of its locomotives using a conversion kit developed by CPKC. “It feels strong," says Corey Davis, director of innovation-alternative fuels and energy management at CSX who test-drove the locomotive recently. “It doesn’t make noise, doesn’t vibrate, doesn’t smell of smoke," he says, adding that hydrogen locomotives in rail yards would be less disruptive to neighboring communities.

Mulligan says he believes that hydrogen locomotives eventually will replace the current diesel-electric locomotive, in much the same way diesel-electric locomotives replaced steam engines by the late 1950s.

But that vision remains far off.

Although hydrogen trains have more energy capacity than battery-powered trains, they don’t have the energy capacity of diesel locomotives, and questions remain about the supply of hydrogen, with the build-out of regional hydrogen hubs around the country still in early phases, which is affecting the cost.

The production of hydrogen, distribution, transportation, storage and fueling facilities for industrial uses are issues that need to be addressed at a national level and not by the rail industry alone, the Association of American Railroads says. Another issue is that the supply chain for hydrogen fuel itself can be energy-intensive—unless the hydrogen is produced from low-carbon sources.

Jim Vena, the chief executive of Union Pacific, which is investing in fuel-efficient diesel locomotives as well as those that can run on biodiesel, says the industry needs to look closely at the overall carbon footprint associated with technologies that require new infrastructure to ensure they don’t actually result in higher emissions.

Esther Fung is a reporter for The Wall Street Journal in New York. Email her at esther.fung@wsj.com.

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