Aside from walking or bicycling or perhaps traveling by electric car, taking the train is often considered the most energy efficient and low emission way to get around. But, determining exactly how efficient or how emission free is a difficult calculation – many questions need to be answered first.
What type of train? Intercity, commuter, subway, light-rail or tram? How many stops? Express or nonstop? A long distance train but a milk-run with a stop at every town? How many passengers on board? Full capacity? Average? Lightly loaded? What type of propulsion? Pure electric with a power grid connection? Diesel electric?