When defining the "most polluting vehicle," the answer depends on whether you are looking at individual emissions or the collective impact of a specific class. Individually, the NASA Space Shuttle (now retired) or modern heavy-lift rockets like the SpaceX Starship are among the most polluting single-event vehicles due to the sheer volume of fuel burned in minutes. However, in terms of ongoing daily operations in 2026, ultra-large container ships and cruise ships are often cited as the most polluting. A single large cruise ship can emit as much particulate matter as a million cars. These vessels often burn "bunker fuel," which is much dirtier than the gasoline used in cars. In the automotive sector, old, poorly maintained heavy-duty diesel trucks and vintage military vehicles are the worst individual offenders. Collectively, however, the standard passenger car remains the biggest contributor to global warming in the transportation sector simply because there are over 1.4 billion of them on the road, out-producing the total emissions of planes and ships through sheer volume.