Can Public Transport Reduce Our Carbon Footprint?

By David Freudberg

Apr. 15, 2011

Most people in metropolitan areas face choices when we travel — to go by car or to use public transit? These decisions have a huge impact on our wallets, on the environment and on our quality of life. We’ll explore these issues in Passengers, a two-part radio documentary airing on WGBH Radio's Humankind at 6-7 pm, Sunday, Apr. 10 and Sunday, Apr. 17 on 89.7 FM. Here, series producer David Freudberg introduces one of the issues covered by the documentary.

Traffic builds up in New York City's Times Square. (Flickr/Qlis)

A MassINC poll released earlier this week showed that 71 percent of respondents believed climate change to be happening, and 61 percent believe it’s mostly due to human causes.
The human activity with one of the highest carbon footprints is transportation, which specifically affects air quality and carbon emissions. But just how much of those things travel produces depends in part on how much you travel and by what mode.

More resources: 

LISTEN: Passengers, Pt. 1

LISTEN: Passengers, Pt. 2

Related articles, information

Google transit: Plan your next trip on public transit  

Walking and bicycling are the cleanest ways to go and can be the healthiest. But other types of transportation – including cars, trucks, planes, buses and trains -- are linked to 30% of U.S. greenhouse gas. Fully 70% of oil consumed in the United States fuels transportation. The rest heats homes and offices and serves other needs.
Many experts consulted for our Humankind public radio documentary series Passengers (part two of which airs this Sunday, Apr. 17 from 6-7 pm on 89.7 FM) conclude that public transit is the most energy-efficient way to travel for the majority of people who use motorized vehicles. That’s because a bus or train often carries a much larger number of passengers than a private automobile, thus reducing the amount of energy consumed – and pollution discharged – per rider.
Compare that with 90% of automobiles, which have just one passenger, the driver. Add to this calculation that with so many single-rider vehicles on the road, traffic jams cause even further pollution as cars burn fuel while stuck in congestion. Technological solutions like more fuel-efficient vehicles make a positive difference, but this has been largely offset by the significantly greater number of “vehicle miles traveled” in the U.S. today, as our population grows.
Among the various modes of public transit, heavy-rail transit (e.g. subways) is most energy efficient and therefore least polluting. This is true even though electric-powered vehicles often derive their power for oil and coal sources.
But today, most trips occur from suburb to suburb, where subways are rare. For suburban travel, buses may be the cleanest motorized mode per passenger.
There are other environmental consequences to our heavy use of automobiles.  According to Dr. Robert Cervero, Director of the University of California’s Transportation Center in Berkeley, impervious paved surfaces cover 45-50% of our cities. This traps heat in urban areas, especially at times of low wind in warm seasons. The resulting “heat island” effect can produce emergency conditions abd drive up energy use (and thus pollution) for air conditioning.
Other environmental effects of automobiles include oil stain runoff into streams, photochemical smog (when sunlight hits pollutants in the air) and health consequences.
In some communities, high temperature and high smog conditions prompt authorities to declare an air alert. In certain Washington, DC area communities, on those days public transportation is free – to lure travelers out of their cars and onto trains and buses.
And as Roy Kienitz, US Undersecretary of Transportation pointed out, greater use of public transit has another benefit: People typically walk from home to the local bus or train stop. This walk, as few as several blocks each way, adds up to healthy physical activity.
A 2010 University of Pennsylvania study found that compared with more sedentary drivers of automobiles, public transit riders lose on average 6.5 more pounds per year. 

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