Trains also have brakes which produce large quantities of fine particles.
This is especially a problem in enclosed spaces with limited ventilation: on parts of the London Underground, air pollution in the tunnels can be many times worse than on the streets above.
Trains are also way more efficient than cars at transporting people. If everyone taking the train was driving instead you can bet air quality would be way worse.
This is especially a problem in enclosed spaces with limited ventilation: on parts of the London Underground, air pollution in the tunnels can be many times worse than on the streets above.