In a much-commented and quoted article by Norman Garrick, a trend is noted in automobile use and purchase. To quote:
What these cities may not realize is that they could be riding the crest of a wave of change in our culture. The tentative signs of the end to the dominance of cars in American culture are showing up in a number of ways. For example, the number of vehicles per person in America peaked in 2001. In fact, this decade is the first since the automobile era began in 1900 that the number of vehicles per person was smaller at the end than at the beginning of the decade. Likewise, the number of miles driven in America for each man, woman and child peaked in 2004 – both of these peaks occurred long before we even dreamed of the current economic downturn which seems to have just accelerated the trends.
Fiscal and physical drawbacks of the automobile dominance of the landscape are the cost of maintaining the highway infrastructure, and the environmental impact of immense tracts of street and highway structures capturing and re-radiating heat in the urban landscape. Other costs are the massive amounts of space to store vehicles for the 80% of the time that they're unused.
A social trend, possibly influenced by economics, appears to be that people are keeping their cars longer and are not as mesmerized by new vehicles. Thus cars are seeing reduced numbers of sales, but ironically more miles traveled.
The rationale for reducing vehicle miles traveled is based upon the manifesto by Congress for a New Urbanism, which bases its planning principles on a walkable, compact urban fabric with smaller traffic grids and cars demoted to second-class status. Lots of people walking and biking to destinations, or using public transit. It's an anti-sprawl methodology that tries to counteract the roof farms that have spread out over the United States. This organization also notes that highways are coming down and being replaced with urban places, otherwise known as freeway rollbacks.
However, there's always a pushback. In a reaction to what are considered anti-auto policies, The Reason Foundation's publication, Mobility First, takes issue with the idea that the auto should be de-emphasized and that auto use drives economic growth, but without mentioning public transit. Or the many cities that are taking cars out of their urban centers and turning them over to pedestrian use.
California is at an interesting crossroads with its intent to force development into communities using the Transit Oriented Development model (TOD), known as SB 375. This is ostensibly to cut down on GHG emissions by reducing vehicle miles traveled (VMT), but analysis is beginning to show that form-based development will not change this much. The local regional government agency, SCAG, continues to insist that this model will achieve the GHG reductions necessary, but in fact the VMT numbers are offset by the growth in construction square footage that this legislation forces into communities. This square footage is responsible for the bulk of energy use and GHG's produced to build all of this new development, hence is not sustainable.
What also has to be considered are the resources consumed - water and energy - and the reduction of urban open space needed for human habitation and interaction with the natural world.