I often try to remember how much each mode of transportation costs the environment. Data published by UK government has good numbers. These data can probably be used as proxy for India with some caveats. The buses emit more carbon and almost certain to carry many more passengers; same goes with trains. I could not find such numbers published for any Indian city. Let’s assume that

• A plane carries 100 passengers.
• A train carries 1000 passengers.
• A car carries 4 passengers.
• A bus carries 100 passengers.
• A bike carries 2 passengers.

Following is the value of cost per person per kilometer (roughly, rounded up for easy to remember). 1 flight = 10 cars = 20 bikes = 50 bus = 100 Trains! It means, “If you travel in a fully occupied flight for a kilometer, it costs environment equal to 10 car kilometers (with 3 co-passengers), 20 bike kilometers (with 1 co-passengers), 50 bus kilometers (with 99 co-passengers), and 100 (diesel) train kilometers (with 999 co-passengers). The most environment-friendly mode of traveling is train. Bus is good choice for inter-city travel. If cars are fully occupied, they are as costly to environment as a bike. Cycling is the best!