As America’s truck and bus fleets transition towards near-zero emissions, advanced internal combustion engines, particularly diesel, remain the dominant choice. According to the Engine Technology Forum, the adoption of near-zero emissions diesel engines increased by 4% in 2023. Despite emerging zero-emission technologies like battery electric and fuel cell vehicles making up a small fraction of the fleet, renewable fuels are playing an increasingly important role in reducing emissions. Continued innovation in internal combustion engines, combined with the growing use of renewable fuels, is essential for achieving long-term sustainability goals in the transportation sector.