People around the world rely on trucks to deliver the goods they need, and so-called long-haul trucks play a critical role in those supply chains. In the United States, long-haul trucks moved 71% of all freight in 2022. But those long-haul trucks are heavy polluters, especially of the carbon emissions that threaten the global climate. According to U.S. Environmental Protection Agency estimates, in 2022 more than 3% of all carbon dioxide (CO₂) emissions came from long-haul trucks.

The problem is that long-haul trucks run almost exclusively on diesel fuel, and burning diesel releases high levels of CO₂ and other carbon emissions. Global demand for freight transport is projected to as much as double by 2050, so it's critical to find another source of energy that will meet the needs of long-haul trucks while also reducing their carbon emissions. And conversion to the new fuel must not be costly.

"Trucks are an indispensable part of the modern supply chain, and any increase in the cost of trucking will be felt universally," notes William H. Green, the Hoyt Hottel Professor in Chemical Engineering and director of the MIT Energy Initiative.

For the past year, Green and his research team have been seeking a low-cost, cleaner alternative to diesel. Finding a replacement is difficult because diesel meets the needs of the trucking industry so well. For one thing, diesel has a high energy density—that is, energy content per pound of fuel. There's a legal limit on the total weight of a truck and its contents, so using an energy source with a lower weight allows the truck to carry more payload—an important consideration, given the low profit margin of the freight industry.

In addition, diesel fuel is readily available at retail refueling stations across the country—a critical resource for drivers, who may travel 600 miles in a day and sleep in their truck rather than returning to their home depot. Finally, diesel fuel is a liquid, so it's easy to distribute to refueling stations and then pump into trucks.

Past studies have examined numerous alternative technology options for powering long-haul trucks, but no clear winner has emerged. Now, Green and his team have evaluated the available options based on consistent and realistic assumptions about the technologies involved and the typical operation of a long-haul truck, and assuming no subsidies to tip the cost balance. Their in-depth analysis of converting long-haul trucks to battery electric—summarized below—has found a high cost and negligible emissions gains in the near term.

Studies of methanol and other liquid fuels from biomass are ongoing, but already a major concern is whether the world can plant and harvest enough biomass for biofuels without destroying the ecosystem. An analysis of hydrogen—also summarized below—highlights specific challenges with using that clean-burning fuel, which is a gas at normal temperatures.

Finally, the team identified an approach that could make hydrogen a promising, low-cost option for long-haul trucks. And, says Green, "it's an option that most people are probably unaware of." It involves a novel way of using materials that can pick up hydrogen, store it, and then release it when and where it's needed to serve as a clean-burning fuel.

More information: Rob Jones et al, Realistic U.S. Long-Haul Drive Cycle for Vehicle Simulations, Costing, and Emissions Analysis, Transportation Research Record: Journal of the Transportation Research Board (2024). DOI: 10.1177/03611981231215672

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