"Research evidence suggests that having a car is a worthwhile investment in better outcomes for low-income families. Recent reports quantify the additional money required to own and operate personal vehicles, as compared to the lower cost of traveling on public transit. However, this method of accounting fails to consider the fact that poor workers without a car may not be able to search for or accept a better-paying job because public transit doesn't go there, causing these workers to lose lost income or benefits as a result. This report outlines opportunity costs experienced by transit-dependent poor households, and concludes that when all costs are considered along with benefits of private vehicles, it makes sense to press for more assistance and policies that reduce car ownership costs for poor workers."
The rest of the article can be found here : http://www.brookings.edu/papers/2005/1128childrenfamilies_waller.aspx