What is the least environmentally friendly way to travel?

Out of all modes of transport, flying affects the environment the most, calculated per passenger and kilometre. But since the vast majority of all passenger journeys take place by car, car traffic has the greatest overall affect.

Driving a car is considerably worse for the environment than traveling by bus, train or subway. Replacing as many car journeys as possible with walking, cycling or traveling by bus, train or subway is the most environmentally friendly measure you can take as a car owner.