Now are we missing the point?
The BBC has a blog called "Ethical Man" that can be amusing. In this particular post where he wonders what is the most efficient transportation available with respect to carbon emissions and he comes out with some surprising conclusions. Flying is not that bad because it flies a lot of people, walking turns out to be very carbon intensive due to our food supply chain and cars with more than one people are more efficient than mass transit.
Some of the arguments are canards of course. We really don't eat food to move around, we eat food to live. So it's going to happen anyway. As for automobiles, the issue ends up being that we create carbon intensive architectures to support the car. Towns and metropolitans were smaller when people walked and took mass transit. Now we live on roads, and roads (in particular freeways) are incredibly costly. But since we as a society fund it collectively we don't notice it. Jet travel poses it's own problems (and given my line of work have two choices, fly or be unemployed).
The question is how de we redefine our economy to be more effective. The internet may solve some of those problems. Videoconference is now how I keep in touch overseas. Hybrids will offset some our emissions, but it won't solve the issues associated with manufacturing a car. Dirty secret, things built to last reduce consumption since you don't have to replace them. One of the amazing inventions of our age is the infusing everything with a notion of fashion in addition to utility. Do you really need that new shirt, well not functionally, but because it is out of fashion. And we all know we are judged by how we look.
Malthus really understood the challenges of population growth, he wasn't wrong we just are able to extend the curve out but we haven't been able to change the shape of the curve. Modern economics plays on a deep understanding of our psyches, our competitive drives. I can't find the source, but in the course of modern medicine we have never eradicated a sexually transmitted disease. The urges and desires are too strong.
So what is the point of this digressive post. The goal is not arguing which is the better form of transport. The question is how do we look at our lives in time and space to work to our urges as opposed to fighting against them. And it's not going to be a simple cost benefit analysis. How much space do we need to live, how long is a reasonable time to wait for transport (can we design a mass transit system based on average wait time), can we figure out zoning to make it possible to get a quart of milk without having to get in your car.
These are the more important questions than which is the better transport.