Vehicle miles traveled reduction targeting, along the lines desired by environmental groups and some members of Congress, is already the law in California, thanks to SB 375, enacted last year.
In the name of greenhouse gas reduction, this law sets greenhouse gas (GHG) reduction targets for each of the state’s 17 metro areas and requires them to draft smart-growth-oriented land use and transportation plans aimed at reducing vehicle miles traveled (VMT). Those that produce the “best” plans to do this will get priority in the allocation of about $20 billion per year in federal and state transportation funding.
The logic chain that underlies such efforts goes something like this: Transportation is a major source of GHGs, and the more people drive, the more GHGs they emit. If their jobs, schools, and shopping are close to where they live, they won’t drive as much. Therefore, government should promote compact, high-density development so as to reduce driving and therefore to reduce GHGs.
When you work through this logic chain with data and numbers, it starts falling apart.
First, all of transportation (including trucking, airlines, barges, etc.) contributes 27.9% of U.S. GHG emissions, according to the EPA. Personal vehicles (cars and light trucks) are 61% of that; hence, personal vehicles are the source of 17% of GHGs, not one-third, as you will often hear.
Second, GHG emissions from vehicles are a function of speed. Stop & go driving (as in congestion) produces much greater GHG emissions than steady-speed driving between 30 and 60 miles per hour (mph); above about 60 mph, GHGs increase fairly rapidly.
Third, there is no hard data showing that people who live in higher densities drive significantly less than those who live in typical suburbia.
Fourth, there is excellent data from the Australian Conservation Foundation showing that among housing types, townhouses have the lowest carbon footprint, single-family suburban houses the second-lowest, and high-rise condo-type dwellings the highest. This logic chain also ignores considerable evidence that traffic congestion increases with urban density—which of course increases GHG emissions.
If the attempts to reduce vehicle miles traveled in these ways succeed, the result will be even greater reductions in mobility than Americans already suffer through from today’s traffic congestion.