Tuesday, June 9, 2009

Why You Shouldn't Take an Empty Bus, and Other Anomalies

Groovy Green's got a link to a fascinating cradle-to-grave study of vehicle energy use and greenhouse gas emissions per passenger kilometer traveled. And the winner is? An urban diesel bus - at peak hours only. During non-peak hours, the same bus is just about the worst offender in both categories.

Urban light rail and commuter trains stack up a lot better than off-peak buses, but I wonder whether the same kind of on-peak/off-peak difference applies; the study doesn't differentiate. (Of course in many cities there are no off-peak trains - just try getting into Boston by commuter rail on a Sunday morning.)

Surprisingly, given the vilification air travel gets these days, the PKT emissions for a jumbo (I assume a full jumbo, which most of them are) stack up just about as well as those for light rail. The operating emissions are higher by far, but building and operating the infrastructure for light rail is responsible for a much higher level of emissions than building and operating airplane infrastructure.

The vehicle-building emissions aren't so startling - the emissions from building cars and trucks (again per passenger kilometers traveled) are more than double those of building aircraft and many multiples higher than those of building rail cars. But because even gas guzzler engines emit fewer greenhouse gases than bus engines, the total PKT emission load of a near-empty bus is almost double that of a conventional gasoline sedan.

The lesson that Groovy Green's Eric Spitzfaden takes from the study is that sharing rides - or, I would think, vehicles - is a real plus. (To your Zipcars, city dwellers!). Another - and the one that surprised me, though of course it makes sense when you think about it - is that mass transit, often cited as a panacea, might not be. It all depends on ridership. In other words, if it doesn't attract riders, the Obama high-speed rail plan we're all so ecstatic about will do a lot more to create jobs than it will to make us a greener country.

Meanwhile, if you're going to DC from New York, you might do less harm to the planet taking a packed plane than a near-empty train.

Weird, huh?

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