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Reducing Greenhouse Gas Emissions Without Reducing Mobility

Focusing on cutting vehicle miles traveled is the wrong approach

Robert Poole
June 9, 2009

This year’s six-year reauthorization of the federal surface transportation program is likely to have far greater impact on our transportation future than anything since the launch of the Interstate highway program in 1956. Many organizations are calling for fundamental changes in the federal role, and while there is certainly much that is dysfunctional about the current federal program, some of the proposed changes could make things worse, not better.

An example is the proposal released on May 15 by Sens. Jay Rockefeller (D-WV) and Frank Lautenberg (D-NJ) of the Senate Commerce Committee. The first item on their list of “Major Goals of the Federal Surface Transportation Policy and Planning Act of 2009” was this: “Reduce national per capita motor vehicle miles traveled [VMT] on an annual basis.” Many of their other goals were either laudable or innocuous, but this one is definitely harmful, as I will explain.

Before getting into the details, however, just imagine a world in which any proposed new toll road (or toll lanes) project would have to demonstrate conformity with a state’s VMT reduction plan, in order to get a federal record of decision allowing it to be built. In other words, you’d have to prove that your new toll road would lead to less driving.

You may think that is highly unlikely to be legislated, but if you think that, you haven’t been paying attention to debates on transportation policy, energy policy, and global warming over the last few years. Reducing vehicle miles traveled is on the wish-list of just about every leading environmental organization. It is part of the agenda set forth in the 2008 Brookings paper, “A Bridge to Somewhere.” And it’s a top priority of a group called America 2050, with backing from the Rockefeller Foundation and several other nonprofits such as the Regional Plan Association and the Lincoln Institute of Land Policy.

Not only that, but VMT reduction is now the law in California, thanks to SB 375, enacted last year. In the name of greenhouse gas (GHG) reduction, this law sets 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 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 working through this logic chain with data and numbers, it starts falling apart. First, all of transportation (including trucking, airlines, barges, etc.) contributes 27.9 percent of U.S. greenhouse gas emissions, according to the Environmental Protection Agency. Personal vehicles (cars and light trucks) are 61 percent of that; hence, personal vehicles are the source of 17 percent of GHGs, not one-third, as you will often hear.

Second, greenhouse gas emissions from vehicles are a function of speed. Stop-and-go driving (as in congestion) produces much greater GHG emissions than steady-speed driving between 30 and 60 miles per hour; 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 VMT in these ways succeed, the result will be even greater reductions in mobility than Americans already suffer through from today’s traffic congestion. There is a small but growing academic literature that finds direct correlations between reduced travel times and regional economic productivity. One key example: if you can go twice as far in a 30-minute commute, your potential-jobs area is four times as large (since the area of a circle around your house is proportional to the radius squared). Some of this research is summarized in the 2008 book Mobility First, by my Reason colleagues Sam Staley and Adrian Moore.

There’s already a lot of momentum for including reduced VMT as one key performance measure in the reauthorization bill, so it’s likely to take a serious effort to keep it out. Besides debunking the logic chain on which it’s based, let’s consider some positive talking points that can help make the case.

First, Americans should demand that proposed transportation-related greenhouse gas reduction measures meet a reasonable cost-effectiveness standard. Both the Intergovernmental Panel on Climate Change and the well-respected McKinsey & Company study, “Reducing U.S. Greenhouse Gas Emissions: How Much at What Cost?” recommend $50 per ton as a good benchmark, below which there are ample opportunities for large-scale but low-cost GHG reduction measures. (In the vehicular area, one of the most cost-effective is miles-per-gallon standards, like the tougher ones President Obama announced in May.) VMT reduction, especially via smart growth land use changes, will surely flunk that test.

Second, instead of setting goals for reduced VMT, we should aim to reduce VHT—vehicle hours of travel. High-occupancy toll (HOT) lanes and new urban toll roads using congestion pricing are excellent at reducing vehicle hours of travel, since reliable time savings are their main rationale. And since congestion pricing can maintain free-flow, uncongested travel, these managed roadways also reduce GHG emissions.

Finally, if we need a slogan, perhaps it could be this: Reduce CO2, not mobility. If we can re-frame the debate in this manner, we might well prevent the enactment of very harmful federal restrictions on driving.

Robert Poole is director of transportation at Reason Foundation.


Robert Poole is Searle Freedom Trust Transportation Fellow and Director of Transportation Policy


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