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Transportation is the largest source of GHG emissions in the United States, making up 29 percent of all emissions. Within the transportation sector, heavy-duty vehicles are the second-largest contributor, at 25 percent. Reducing GHG emissions is a critical step in reducing the probability of impacts from climate change, including heat waves, drought, sea level rise, extreme climate and weather events, coastal flooding, and wildfires. Some populations may be especially vulnerable to damages associated with climate change, such as the very young, the elderly, low-income people, the disabled, people of color, and indigenous populations.

EPA previously took action to reduce GHG emissions from heavy-duty trucks with its Phase 1 and Phase 2 GHG standards. With this action, EPA would revise GHG standards for all heavy-duty vehicles and engines to go beyond the existing standards. These new GHG standards would begin as soon as model year 2030.