So you have a car, and not only do you feel a wee bit of carbon footprint guilt every time you start the engine, you just plain can't afford $71 a pop to fill up the tank. But for whatever reason, you can't quite give that fossil fuel fiend sitting in the garage up completely. I'm in the same boat. I need my car just enough to justify owning one (I won't get into details here- the most important thing I've learned being an environmental evangelist is to cut the judgment).
Rather than thinking: "I should drive less" I've come up with a rule system that really work for me. I make rules for my life (I've done it with everything from donut consumption to running) and once it's a rule, I HAVE to stick by it. The key is not to make too many rules for yourself but to pick the most important. And there's nothing more important than preserving the planet by reducing your carbon emissions. Here's are my drive-less rules that I stick by:
Drive on a Schedule: I only allow myself to drive on the weekends. Period. Unless there's an emergency, my car stays in the garage Monday-Friday (I give myself a break on holidays too). Since it's a "rule" (rather than a passing thought) that I've made for myself for a good reason, I treat it as such- like stopping at a red light- you only break it in an emergency.
Don't Drive if There's Public Transportation: I work from home but have frequent meetings in New York, and I can walk to the station and take the commuter train. I used to drive to the city on off hours when I knew traffic would be smooth. But now the rule is that if I'm going into Manhattan, I take the train. No excuses.
Combine Trips: You've heard this one before; turn it into a rule by deciding a minimum number of errands or stops per trip that's expected before you turn the engine key. I think three is pretty good, though obviously 4 or 5 is better. Since lots of parents spend time and money driving their kids around, turn it into a game for kids by getting them to figure out how few car trips can be made in a week by combining what they need and want to do (this is a great way to teach them about schedules and organization too).
Have Stuff Delivered: This is a good option for items that you drive a distance or make special trips for. Often you can find some products (like pet food) for less money online, even including shipping costs. The UPS or FedEx vans are driving around anyway, so you may as well get them to do the driving (think of it like public transportation for your stuff). DON'T do this if the products are available somewhere you have to stop anyway.
Walk or Cycle: Yeah, we've heard this before- make it work by making a rule that if a destination is within a certain distance (a mile for walking works for me) you'll strap on those comfy sneaks or flats(that you keep right by the door-make it easy on yourself!). Even if it's rainy or pretty hot, a mile only takes about 12-15 minutes so it's not unbearable. If a mile's too far, make it a 1/2 mile (which should only take 6-8 minutes). Obviously, you can stretch the distances if you have a bike.
Basically these rules all break down to the same basic point: Think before you drive and treat the car as a privilege rather than a joyrider. BONUS- You'll enjoy driving more when you do it less often.