I created this graph for the wikipedia article on the Effects of the automobile on societies. (It's based on a similar graph in the book Transportation for Livable Cities By Vukan R. Vuchic, a great read for anyone interested in sustainable development.) The wikipedia article still needs a lot of work, but I wanted to share this graph with the people at dailykos.
People tend to choose a mode of transportation based on the out-of-pocket cost. The value above the line represents the out-of-pocket cost per trip for each mode of transportation, the value below the line accounts for subsidies, environmental impact, social and indirect costs.
This graph shows how our government policies about parking, public roads, and tolls make driving a more attractive option for many people in US cities. This is why changing planning policy, eliminating parking lot requirements, increasing the gas tax so that fully covers the costs of highway construction and the other social and environmental costs of driving is so important for creating sustainable, inter-modal transportation systems in our cities.
Notice that, in an urban area, the total cost of both bus and rail systems is lower than the total costs of using a car. But when people make the choice to drive each day they tend to think about the out-of-pocket costs of driving (gas) rather than considering the indirect costs of car ownership, auto insurance and car maintenance. People are even less aware of the fact that the gas tax, at its current level, is not high enough to cover all of the costs of road maintenance. The environmental and social impacts of driving (such as the impact it has on public heath, and the cost of policing the roadways, recovering stolen cars, and dealing with accidents) are even harder to see.
However, when there are tolls, and when municipal parking is priced at the market rate, rather than being under-priced or free, much of the subsidy vanishes. Under these conditions, public transportation is a competitive option when considering out-of-pocket costs. This is the situation in many cities in Europe where people drive much less and transit is more diversified. This reduces pollution and, combined with incentives for fuel efficient vehicles, could go a long way to making our cites a little more efficient economically, safer, and more green.
MORE ABOUT THE GRAPH:
This graph does not show intangible costs that are hard to quantify in monetary terms, such as convenience, time, lives lost in auto crashes, Injuries from auto crashes and the social impact of urban sprawl. The "social costs" in this graph are based only on the impact of inefficiencies introduced through greater congestion. (That is a reduction in carrying capacity of roads.) One might argue that the disparity would be even greater if these additional factors were introduced.