[vinay427]

It's reasonable that if GP needs and already has a car for other non-commuting purposes (shopping, road trips, etc.) the choice in their specific case is between paying for public transit and only paying for gas to cover the commute.

[dionidium]

I understand what you're saying; it's just not a reasonable way to perform a complete or useful cost analysis.

[StudentStuff]

Cost of insurance and wear & tear are direct costs of each trip outside gas, not including those (which is ~50% of the cost of each trip) is deceiving yourself.