I just did the math. According to this, its more economical for me to drive to work than it is to walk.
Driving:
0.5 miles x 5 days = 2.5 miles/week ÷ 20 mpg = 0.125 gal/week x $4.00 /gal = $0.50/week x 2 trips (morning & evening) = $1.00/week
Walking:
http://www.csrees.usda.gov/newsroom/impact/2008/nri/03191_food_prices.html
http://www.foodreference.com/html/a-low-calorie-cost-1208.html
Based on a standard 2000-calorie diet, the researchers found a diet consisting primarily of calorie-dense foods costs $3.52 a day, but a diet consisting primarily of low-calorie food costs $36.32 a day. The average American eats a variety of foods throughout the day, spending $7 a day. -March 19, 2008 [Bold values used below]
http://www.fitwatch.com/phpscripts/viewexercise.php?descr=walking,%20general&mets=4.0
0.5 miles = 10 minute walk = 44 calories
2000 cal ÷ $7.00 = $0.0035 /cal
44 cal x 5 days = 220 cals/week ÷ $0.0035 = $0.77 /week x 2 trips (morning & evening) = $1.54/week
If I had a hybrid vehicle that got, say 40 or 50 mpg, then there’d be no contest.