Not-So-Quick and Not-So-Dirty Solutions to Decarbonize Off- Road Vehicles

sı Supporting Information T ransportation emits a considerable amount of green- house gases (GHG), for example, in 2022, it was responsible for about 33% of the United States GHG emissions. 1,2While the transportation decarbonization efforts through electric vehicles have sped up in recent years, 3 we still face barriers to their adoption.Additionally, as Figure 1 shows, they only represent half of the solution.The remaining half is due to other transportation modes like buses, trucks, planes, trains, and ships.Each of these transportation modes has unique requirements and accordingly, in many cases, a wellengineered solution is not ready for deployment.For example, the fuel cell technology is mature enough for light duty vehicles but requires further research and development for heavy duty trucks, 4 and efforts like the Million Mile Fuel Cell Truck consortium 5 are required to bridge this gap.Alternatively, more stringent requirements of aviation, rail, and marine applications demand that we judiciously combine new technology development 6,7 (e.g., energy-dense beyond lithium-ion batteries) with deployment of specialized solutions 8-10 like nuclear-powered ships.In comparison, off-road vehicles, i.e., construction, mining, agricultural and other machines operating away from roads, emitted the same GHG amount in 2022 as aviation, rail, and marine transportation combined, 1 but there is minimal discussion of decarbonizing this transportation mode in the scientific literature (refer to Figure S5 and related text for a more detailed breakdown of the off-road vehicle emissions).As the global population rises and the living standards improve, off-road vehicle use will increase for constructing more buildings, mining more minerals, 11 growing more food, operating warehouses and industries, and supporting aviation, rail and marine operations.Recent geopolitical tensions have further underscored the importance of bolstering these sectors critical to our material supply chains. 12Despite such profound importance of off-road vehicles, most discussions omit their decarbonization potential, 13,14 let alone acknowledge their environmental impact.While few existing discussions pledge to decarbonize this sector, [15][16][17][18][19][20][21][22][23] corresponding projections report an uncertain future since they assume that the presentday technologies, e.g., costly lithium-ion batteries, will be used to decarbonize the off-road vehicles 2,16,17,[23][24][25] (the question mark next to the off-road vehicles in Figure 1 symbolizes such uncertainty as opposed to focused efforts driving decarbonization of other modes).We instead rephrase this quest of decarbonizing off-road vehicles in terms of developing new