Reduces Greenhouse Gas Emissions — 85% of greenhouse gas emissions that are released every day come from day-to-day commutes. By choosing to use public transportation, less fuel will be burned and air quality may see an improvement.

Paradoxically, while a single bus or train emits more pollutants than a single car, public transportation as a system is one of the most effective ways to decrease overall urban pollution. By consolidating dozens or hundreds of passengers into a single vehicle, mass transit significantly reduces the "per capita" carbon footprint and nitrogen oxide (NOx) emissions compared to individual private cars. In 2026, many cities like San Francisco, London, and New York have transitioned their fleets to electric or hybrid-hydrogen buses, further widening this gap. Studies show that taking public transit instead of driving alone can reduce a person's CO2 emissions by up to 45%. Furthermore, robust public transit reduces traffic congestion, which prevents the high-pollution "stop-and-go" idling of thousands of private vehicles. While the construction of rail lines has a high initial environmental cost, the long-term impact is a drastic improvement in air quality and a reduction in the "fine particulate matter" (PM2.5) that contributes to urban smog and respiratory illnesses.