The single most effective way to cut one's personal quotient of carbon dioxide pollution is switching from cars to public transit. That's the finding of the American Public Transportation Association, which this week released a new report on CO2 and personal transportation. According to APTA, "when compared to other household actions that limit carbon dioxide (CO2), taking public transportation can be more than ten times [more effective] in reducing this greenhouse gas." It's something we all know intuitively, of course--driving alone has significant climate impacts even if the car we're driving is a "green" one--but it's fascinating to see the specific impacts of our driving habits quantified.

The APTA study took on four big questions:

• How much CO2 is public transportation currently saving in the US?
• How much additional CO2 savings are possible if public-transit use increases?
• What's the carbon impact of a household whose members drive to work instead of using public transit, and how can households reduce that impact? And
• Does public transit lead to better land use (and thus environmental and social benefits)?

In 2005, the APTA researchers found, public-transit use reduced CO2 emissions in the United States by 6.9 million metric tons--the net difference between the emissions produced by transit and the emissions prevented by reducing congestion and taking cars off the road. A single individual with a 20-mile commute could reduce her personal carbon production by more 20 pounds a day simply by switching to public transit. And although it's hard to precisely measure the land-use impacts of increased transit use, various studies have estimated that the number of vehicle miles traveled goes down between 1.4 and 9 miles for every passenger-mile traveled on transit.

That personal carbon reduction deserves a closer look. Twenty pounds a day works out to more than 4,800 pounds a year, assuming a 240-day work week. That impact is much greater than many other changes people are frequently encouraged to make, including weatherizing the home and adjusting the thermostat (about 2,800 pounds a year); replacing incandescent bulbs with compact fluorescents (about 90 pounds per bulb a year); and replacing an old refrigerator with a high-efficiency one (about 335 pounds a year).

But the decision to trade driving for public transit isn’t merely a matter of individual choice: the transit must be available. Typically, to make that happen, governments must support it politically and financially. Fortunately, better mass transit is a solution more municipalities are embracing, according to data tracked by the Federal Transit Administration, which include transit ridership, availability, and subsidies nationwide. According to the latest available numbers, the number of miles transit vehicles spent in revenue-generating service went up 31 percent between 1996 and 2005. Systems that were built in that period (mostly light rail) saw much larger gains: 85 percent for light-rail systems, and a nearly three-fold increase for vanpools. Buses continue to make up more than half of all transit systems nationwide, but light, heavy, and commuter rail systems continued to grow: from a combined total of 36.6 percent in 1996 to 39.3 percent in 2005.

Image: flickr/anaki

I'll have to look at the study, as I've been hearing compelling arguments about going vegetarian as well...

but great piece!

Posted by: Alex Steffen on September 27, 2007 9:09 AM

Hey, nice piece. I thought this was common knowledge already, of course. :)

Posted by: Ben Schiendelman on September 27, 2007 3:58 PM

I recently heard that eating a vegetarian diet would do more to reduce carbon emissions than stopping driving. It doesn't really make sense to me, though.

I'm participating in conducting a survey in Berkeley about people's travel habits. It's true that people will never use public transit unless it improves, and I cannot blame them. I hope local governments are seriously going to make the effort in the coming years.

Posted by: Marcy Sheiner on September 27, 2007 4:55 PM

I take public transit to work now, and we are factoring transit routes into our house search. However, there are significant limitations on public transit in our part of Los Angeles. While we have good access to a bus line where we are now, it's the transfer process that is cumbersome.

One of the simplest ways to make the bus a more appealing alternative to the car would be to change the weekend schedules. If the bus ran more often, I'd find it much easier to run errands that way, because I wouldn't have the significant delays (Now I'm reluctant to go to, say, the grocery store because of how long perishables would be sitting in the sun). Shorter intervals between buses would also make the transfer process. But it's difficult to be enthusiastic about a weekend bus trip that takes an hour in each direction, when the drive is only 10 minutes each way.

Posted by: Kate on September 27, 2007 5:59 PM

ECB, what about not having to commute by vehicle at all. I'm all for transit, but it's sort of suspicious about who's putting out the info. What if we were just able to walk to work, school, job, doctor,etc?

Posted by: Brice Maryman on September 28, 2007 3:21 PM

Yes, eating vegetarian (or even better, vegan) could have more of an impact. (I guess depending on how far you drive.) This article is a good overview:

http://www.iht.com/articles/2007/06/06/business/greencol07.php

Consider that most animals you eat may be fed around 10x their final weight in grains. Someone has got to grow and transport all those grains, not to mention deal with the fertilizers for the plants grown to feed them, waste products from the animals, etc etc.

Posted by: Mike on September 29, 2007 10:58 PM

Nearly half of the CO2 reduction claimed in this study comes from reduced congestion on the roadways, and the study as I read it is also only comparing public transit to single-occupant vehicles, not to cars in general.

This point should be very encouraging to those of us who don't have access to good public transit systems on the routes we normally travel, since it indicates that carpooling can be as good as public transit at reducing emissions.

Especially large companies (Here's hoping someone at Google reads this) could offer a ride-sharing program that would match potential ride-sharers based on home addresses and normal working hours. To make it more flexible (since I think one of the biggest reasons people don't carpool is concerns over one member of the carpool having to stay late to finish a project or leave early to pick up kids, etc) there could be an social networking system to match up people whose carpools aren't working on a particular day (i.e. if we're supposed to carpool today, but I have to leave to pick up my kid, you can post to a system that will send requests for a ride to others who live near you and share similar working hours). The system could also include a bus-of-last-resort for those who in the end, can't get a ride.

The social networking aspect would also make it possible for a company to quantify the reductions in driving achieved and monetize those reductions in the form of carbon credits.

Posted by: Bert on October 1, 2007 9:20 AM