Worldwide, commercial vehicles are the largest growing contributor to air pollution, fuel consumption, and global warming emissions in the on-road transportation sector. As with passenger vehicles, there are a variety of fuel, engine, and powertrain technology options for trucks and buses that can reduce criteria pollutant and greenhouse gas (GHG) emissions compared with conventionally-powered diesel and gasoline vehicles. Examples of these advanced technologies include hybrid-electric, plug-in hybrid-electric, and hybrid hydraulic-powered drivetrains.