The “big three” have all announced that they will extend their employee discount to all customers through August 1st, making the battle to get people out of cars and using mass transit all the more uphill. The G8 bombings have also steepened the slope.

The move by Ford, Chrysler, and GM highlights one of the disadvantages that proponents of mass transit face regularly though — the fact that once a person buys a car, there is a large incentive for that person to put many many miles on it. The cost to the owner of the first few miles of driving after buying the car is incredibly high, since the cost per mile is the full cost of the car divided by only a few miles. In order to get the most out of the purchase, and to not feel like a complete idiot, the car has to be driven a pretty significant number of miles. Other overhead costs are present with cars as well, such as insurance and possible parking considerations.

Mass transit has no such overhead. While some systems have monthly or even yearly passes, there is no mode of transport that locks the user in quite like the automobile.

In a lot of ways, though, modes of transportation are changing and getting away from this simple dichotomy. The Zipcar is one way the overhead for cars is being eliminated, collapsing all costs into an hourly rental rate. Zipcar also claims some green benefits: reducing total miles driven by 50 percent and eliminating the need for up to 10 privately owned cars. The reason, according to their website, is that “people have to pay the full cost of using the car each time they drive,” and so “they choose to drive only when it makes economic sense.” It’s only in a few places along the east coast right now but is expanding to fourteen more cities all over the country soon, and is already popular in Europe.