If I didn't have to have a vehicle, I wouldn't have one. Period.
I've done the math and I would save about 9k per year (gas, insurance, maintenance, repairs --not including a car payment if you had one). Your mileage may vary (no pun intended).
Lately, I've been staying in that 55-60mph range (sweet spot for my vehicle), taking my foot of the gas completely when going downhill and slowing up considerably before red lights whenever possible. Sometimes it's not always safe to do that, but when you can it definitely helps.
RE: How To Get Better Gas Mileage, Contributed by @sharingeverybite