standard, cut emissions per vehicle-mile by over two orders of magnitude, reducing an LDV’s direct conventional air pollution impacts to nearly negligible levels. Quantitatively, the CAA policies addressing emissions have been by far the most effective areas of policy, resulting in a substantial absolute reduction of conventional pollution from LDVs even in the face of rising VMT (see Figure 6.1).

The CAA’s overarching requirement for healthy air, embodied in the National Ambient Air Quality Standards (NAAQS), is what ultimately anchors the policy. The law obligates the U.S. Environmental Protection Agency (EPA) to pursue fact-based assessments of air pollutants’ impacts on public health and welfare and to promulgate NAAQS solely on that basis. Economic considerations can enter in only when EPA develops the regulations that determine how the NAAQS will be met.

The Supreme Court (2007) interpreted the CAA’s definition of air pollutants to include greenhouse gases and said that they could be subject to regulation if found to endanger public health or welfare. The EPA subsequently made such an “endangerment” finding (2009), setting in motion a regulatory process that started with GHG emissions standards for motor vehicles and is being extended to other sources.

6.1.5 Technology Policy

A large number of policy measures have the potential to influence technical innovation in LDVs and fuels. The federal department involved most actively in directly promoting new automotive technology has been the DOE. Its role primarily has been one of funding basic science and engineering research related to vehicles and fuels and pursuing demonstration and deployment programs that might foster market adoption of the technologies developed. Many National Research Council (NRC) studies reviewed this research, development, demonstration, and deployment approach while suggesting refinements and highlighting the challenges and obstacles involved. Examples of such energy technology policy programs include the Advanced Battery Consortium, the Partnership for a New Generation of Vehicles, the hydrogen-oriented FreedomCAR program, and the present US Drive program that emphasizes electric vehicles and plug-in hybrids. From the 1970s forward, parallel efforts have been aimed at developing renewable fuels.

6.1.6 Decision Making Through the Matrix of Policy Arenas

Based on methods of technology assessment and economic analysis as discussed below in this chapter, policy measures are established through a matrix of policy arenas such as those outlined above. The preceding overview of the different arenas of public policy that influence the LDV sector—transportation, land use, environmental protection, energy, and technology—underscores the complexity of the challenge from a practical policy-making perspective. A national decision to reach goals such as those given in this committee’s statement of task will likely need to involve all of these different policy arenas and the associated diversity of congressional committees, federal agencies, and stakeholder interests, along with an analogous range of interests at state and local levels of government. Reaching a national decision to achieve the goals will be a complicated undertaking that requires an adaptive policy framework as discussed below in this chapter.


Policies that affect petroleum use, GHG emissions, or both ultimately exert their influence through a few key parameters:

  • Vehicle energy intensity—typically, the energy required to move the average vehicle of the on-road LDV fleet 1 mile;
  • Petroleum share of the energy used to power LDV fleets (when energy security and dependence on petroleum is the issue) or net GHG emissions balance of the fuel system (when climate disruption is the issue); the latter is often described as the average well-to-wheels GHG emissions of the energy used to power the vehicle fleet;3 and
  • Volume of travel—typically, the VMT by the on-road LDV fleet.

It sometimes is argued that system efficiency constitutes an independent fourth parameter, but that is not the case. Policies that affect system efficiency influence GHG emissions or petroleum use only through one or more of the three parameters listed above.4

A common analytic framework for transportation energy and climate-change analysis involves factoring emissions based on the three key parameters, which interact multiplicatively. Addressing all three (vehicle energy intensity, petroleum share of energy use in LDVs, and travel activity) is important because a policy that focuses only on a single parameter is likely to require it to be pushed to extraordinary lengths.5

Whether the policies target one or more of the parameters, they operate by influencing market actors whose decisions determine the values of the parameters, which in turn determine LDV petroleum use and GHG emissions. Policies that


3For advantages and disadvantages of the use of well-to-wheels approaches to regulating GHG emissions related to fuels, see below.

4However, in view of the interest in policies promoting system efficiency, they are discussed below in this chapter.

5For example, the average on-road fleet fuel economy would have to exceed 180 mpg if vehicle energy intensity were the only parameter targeted for reducing LDV petroleum use; see footnote 2 in Chapter 2.

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