The health and environmental impact of transport is significant because transport burns most of the world's petroleum. This causes illness and deaths from air pollution, including nitrous oxides and particulates, and is a significant cause of climate change through emission of carbon dioxide. Within the transport sector, road transport is the largest contributor to climate change.
Environmental regulations in developed countries have reduced the individual vehicle's emission.However, this has been offset by an increase in the number of vehicles, and increased use of each vehicle (an effect known as the Jevons paradox).Some pathways to reduce the carbon emissions of road vehicles have been considerably studied.Energy use and emissions vary largely between modes, causing environmentalists to call for a transition from air and road to rail and human-powered transport, and increase transport electrification and energy efficiency.