Going green is the new black — everyone’s doing it, and everyone has their favorite way of giving back to Mother Nature. Every little bit of energy savings adds up — or rather, subtracts from your carbon footprint, but few things you can do will have as great an effect on the environment as using mass transit systems on a regular basis.

Why It Matters

Transportation-related emissions account for about 28 percent of the greenhouse gasses in the United States, making transportation the second largest contributor to greenhouse gas emissions, according to the U.S. Department of Transportation. Private vehicles, including cars, SUVs and pickup trucks, make up 64 percent of that figure. Increasing the use of mass transit can decrease the amount of carbon released into the air.

How Much It Matters

A single-passenger vehicle releases just under a pound of carbon dioxide for every mile it travels. That’s .96 lbs. of carbon per passenger mile. By contrast, taking the subway puts out only .24 lbs. of carbon dioxide per passenger per mile — a savings of .72 lbs. of carbon dioxide for every mile you travel. Commuter rail produces about .35 lbs. of carbon dioxide per passenger mile traveled. A typical 40-passenger bus reduces the amount of carbon dioxide produced to .65 lbs. per passenger mile, a savings of over 30 percent. Even when you add in the increased amount of emissions produced in manufacturing and maintaining mass transit systems and vehicles, they produce less carbon dioxide than single-passenger vehicles, says the DOT.

How Much It Could Matter

The DOT figures assume average usage of the various forms of transportation. Buses, for example, typically carry only one-quarter of the passengers that they could. When there are more people riding the bus, the savings are even greater. The vehicle uses about the same amount of fuel, but it transports more people. When a bus is full to capacity, the pounds of carbon dioxide produced per passenger drops from .65 to .16.

What Difference You Can Make

If your daily commute is about 10 miles in each direction, and you switch from driving to taking public transportation, you’ll reduce your family’s carbon footprint by about 4,600 lbs. That amounts to a reduction of greater than 8 percent for the typical household — more than swapping out your light bulbs for compact fluorescent lamps and insulating your attic combined.

Added Bennies

While the environment benefits if you choose to take public transit instead of your car, Mother Nature isn’t the only one that gets some goodies out of the deal. A study carried out in Charlotte, North Carolina, before and after the opening of a light-rail transit line suggests that taking mass transit could help you meet your exercise and weight loss goals. The study, published in the August 2010 issue of the “American Journal of Preventive Medicine,” found that people who switched to the light-rail system had more positive views of their neighborhood, were more likely to meet their recommended daily physical activity goals and reduced their BMI by an average of 1.51.