Why do we drive more than necessary even though it harms the planet?

It all has to do with the fundamental evil of human nature.

Or, to be more specific, the urge for power regardless of the costs.

Achenblog (Joel Achenbach) explains:

If I could change one thing about myself it's the way I'm the embodiment of all that is wrong with America and the human species more broadly. Don't get me wrong - my self-esteem is in the normal range, but if I could tinker with my existence it would be to make myself something other than a detestable, oozing, suppurating lesion on the body of civilization.

Time constraints prevent a full accounting of what I'm talking about here, but let's take a look at just one example: I am a self-indulgent motorist.

On weekends I engage in countryside motoring as if it's a form of exercise. Worse, during the week, despite the availability of mass transit, I almost always drive to work, a five-mile jaunt on surface streets past one bus stop after another.

Why do I drive? Power. Raw, unbridled power, at my fingertips and toetips.

My Honda Accord is an empowerment device. It gives me the option of going anywhere on the spur of the moment without heed of bus schedules or fear of Metro delays. I could just start driving, and head West, across the continent, and then veer down through Mexico, and onward to Patagonia. Having a car is like sitting in a restaurant near the door. ...

Now, you might declare that global warming and energy insecurity, not to mention urban sprawl and pollution, have intensified the sin of indulging one's motoring desires. And I would not argue with that point. You're right. I am a bad man. And let us note that advertising campaign (I've seen it all over the place -- from some fossil fuel company I think) in which smiling people are seen thinking to themselves, "I will leave the car at home" or "I will take the bus more often" and whatnot. All this is good. But over the long term, if you want to develop a new transportation and energy policy, you'd probably want to err on the side of assuming that people won't change much. And it is human nature to like to be empowered.