While that isn't a good question, it isn't always valid. Once someone has a car, most of the costs are already sunk. You pay for the car and insurance even when it is sitting at home. The variable costs of a car are very low, so when comparing a car you already have to transit the incremental costs of taking the car are tiny. Transit looks even worse when you have a family and notice that the variable costs of taking the car don't change why the costs of transit go up per family member.

The only time your question matters is if/when the transit system is useful enough that someone can actually consider selling a car. I sold my car to ride the bus to work. However the one week my wife's car was in the shop convinced us that we won't be doing without a car anytime soon. (We often take trips that are 5 minutes by car that were 55 minutes by bus! Then there is the annoyance of the one time we missed the bus)