Wednesday, November 26, 2008

How 'green' is public transit, really?

Slate e-Magazine's Green Lantern takes a look at environmental questions, and this week they took a look at just how environmentally-friendly public transit travel really is. At first glance it looks like a simple question, but when you factor in the infrastructure costs and the wasted resources for low-ridership (but still necessary) trips, it gets a little foggy. Here's part of what the Green Lantern had to say:

"A train produces more emissions per trip than any car, bus, or truck; it makes up for that fact environmentally because it carries a lot more people. It stands to reason, then, that if you ride in a full sedan on a day when the train is pretty empty—and, in particular, if you are in a fuel-efficient car—the car could conceivably be greener per passenger mile. (The study says a car would need to have about three passengers—double the average—to break even environmentally with the typical train.) The numbers are even more striking for buses, which can experience extreme variability in ridership between peak and nonpeak hours. At peak hours—with 40 riders onboard—the Berkeley researchers find that buses often look like the greenest option, producing fewer greenhouse-gas emissions than even the average train per passenger mile. At off-peak hours, a bus looks a lot worse, performing even more poorly than a gas-guzzling pickup truck.

"Does that mean we shouldn't run buses or trains during off-peak hours? No. If you want people to ride public transportation at rush hour, you need to make it possible for them to get around the rest of the day, too. (Not to mention the fact that some people—for either physical or economic reasons—simply can't drive.) And as long as those buses and trains are kept running, it's better—environmentally speaking—to take public transportation, since the marginal impact of your trip will be very low."


Dwight Williams said...

Not sure I'd drive solo even with a ZENN car under me...

Anonymous said...

This is assuming that the train in question is diesel, I assume? I have a hard time imagining an electric train polluting more...

Neil said...

I was disaaponted to not see any media coverage of the impact on the environment during the bus strike.

It seems to me this strike is a great opportunity to confirm or disprove our faith in the environmental benefits of our mass transit system.
Conventional thinking is that mass transit reduces air pollution. Some say each bus trip removes about 40 vehicles from the road.

Here are some research angles that should have been or should be prusued:

Did anyone measuring the air quality in the city during the bus strike to be able to compare it to equivalent days with bus service? Did the air quality been improve or deteriorate during the strike?

My experience was that limited downtown parking and the small number of roads from the suburbs to downtown is forcing bus riders to car pool. Also, in recent years many car owners have opted for more fuel efficient and low emission vehicles. These factors may impact on what we have thought are the environmental benefits of buses. Also, remember that all those busy express buses spend half the tim on the road running empty to the burbs in the morning and to downtown inthe afternoon after each trip delivering passengers.

Another way to research the environmental impact would be to study be the gasoline consumption rate in the city during the strike. did we use more gas? If so, how much more? What would have bene the estimated impact in terms of air wuality, and would that have more than offset the reductions in emissions that resulted form not running buses?

Coudl some PH D in environmental sudies look into this for us?