It's not just gas, but the overall car wear & tear that I anticipate saving on. If I commute til, say, November by bike I'd guess I'd save $600 on gas, $650 on new tires, and there's always that turbocharger I may need to replace which would run me about $800. Add another $50 for an oil change. Total: $1300-2100.

But mostly I want to bike to get off the highway and get my body moving.