Through the emissions from combustion of fossil-derived fuels, transportation systems contribute to degraded air quality, as well as a changing climate. Transportation also leads to noise pollution, water pollution, and affects ecosystems through multiple direct and indirect interactions.

Transportation is a critical environmental issue because it is one of the largest contributors to global greenhouse gas (GHG) emissions, accounting for approximately 20–25% of CO2 emissions worldwide in 2026. The primary problem is the reliance on fossil fuels—gasoline, diesel, and jet fuel—which release carbon dioxide, nitrogen oxides, and particulate matter when burned. This contributes to both global climate change and local air pollution (smog), which has direct health impacts on urban populations. Beyond tailpipe emissions, the infrastructure required for transportation—roads, parking lots, and airports—leads to habitat fragmentation and the "urban heat island" effect. Additionally, the life-cycle of vehicles, including the energy-intensive mining of lithium for EV batteries or the disposal of old cars, creates significant environmental footprints. Transitioning to "decarbonized" transport, such as high-speed rail, electric buses, and sustainable aviation fuels, is the primary goal of 2026 environmental policy, as the world struggles to balance the human need for mobility with the ecological need for a stable climate.