Leave Car at Home Once a Week?

I'm on a new kick to do my part to save money and help the enviornment.  I'm going to see if I can keep the car at home at least one day a week.  I drove to work and brought enough cloths/food that I will not need to have it tonight.  I'll run home tonight, then run to work in the morning leaving the car at work overnight.  Even though I live pretty close, I burn about a half a gallon of gas a day or about $1.50 a day for gas/maintenance.

Got 12.6 miles in yesterday.  Eight miles in the morning 1:05:46, then 4.6 miles on the treadmill in 34:50.  Today I hit 7.2 miles in 59:41, and will be able to get 3.7 more miles tonight running home.  Looking forward to about a 70 mile week and a nice 50K run this weekend, it looks like nice weather.