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Transitions to Alternative Vehicles and Fuels (2013)

Chapter: 1 Introduction

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Suggested Citation:"1 Introduction." National Research Council. 2013. Transitions to Alternative Vehicles and Fuels. Washington, DC: The National Academies Press. doi: 10.17226/18264.



Internal combustion engines (ICEs) operating on petroleum fuels have powered almost all light-duty vehicles (LDVs) for a century. The dominance of ICEs over steam and batteries has been due to their low cost, high power output, readily available fuel, and ability to operate for long distances in a wide range of temperatures and environmental conditions. Although ICEs can run on many fuels, gasoline and diesel have remained the fuels of choice because of their low cost and high energy density, allowing hundreds of miles of driving before refueling. Crude oil has remained the feedstock of choice for these fuels because production has kept pace with demand and world reserves have actually been expanded as a result of ongoing technological progress. The co-evolution and co-optimization of ICE and petroleum-based fuel technology, infrastructure, and markets have proven resilient to challenges from market forces such as oil price spikes in a geopolitically complex world oil market as well as environmental policies such as tailpipe pollution reduction requirements.

For nearly 40 years, energy security concerns have motivated efforts to reduce the use of petroleum-based fuels. LDVs consume about half the petroleum used in the United States, and about half is imported, tying Americans to a world oil market that is vulnerable to supply disruptions and price spikes and contributing about $300 billion to the nation’s trade deficit (EIA, 2011).

More recently, concerns have been growing over emissions of carbon dioxide (CO2), the most important of the greenhouse gases (GHGs) that threaten to cause serious problems associated with global climate change.1 Petroleum use is the largest source of GHG emissions in the United States. Because LDVs account for the single largest share of U.S. petroleum demand and directly account for 17 percent of total U.S. GHG emissions (EPA, 2012), they have become the subject of policies for mitigating climate change.

For these reasons, U.S. policy makers seek to both improve the fuel efficiency of LDVs and promote the development and adoption of alternative fuels and vehicles (AFVs). Here “alternative fuels” refers to non-petroleum-based fuels, including plant-based fuels that are otherwise essentially identical to gasoline or diesel fuel, and to powertrains much more efficient than today’s or capable of using alternative fuels, including non-liquid energy carriers such as natural gas, hydrogen, and electricity. Numerous studies have addressed these issues over the years, reflecting the interest in these goals. Substantial but uneven progress has been made on LDV efficiency, and a small but significant penetration of hybrid electric vehicles in the marketplace has contributed to this goal. Otherwise little progress has been made on AFVs in the marketplace beyond the quantities of ethanol still used almost exclusively in gasoline blends.

Since its beginnings over 100 years ago, the automotive sector has succeeded through a combination of private market forces and public policies. The energy use and GHG emissions challenges with which we now are grappling are the unintended and largely unforeseen by-products of that success.

This report is the result of a study by a committee appointed to evaluate and compare various approaches to greatly reducing the use of oil in the light-duty fleet and GHG emissions from the fleet. As specified in the statement of task (Appendix A), the Committee on Transitions to Alternative Vehicles and Fuels was charged with assessing the status of and prospects for technologies for LDVs and their fuels, and with estimating how the nation could meet one or both of two goals:

  1. Reduce LDV use of petroleum-based fuels by 50 percent by 2030 and 80 percent by 2050.
  2. Reduce LDV emissions of GHGs by 80 percent by 2050 relative to 2005.


1As used in this report, GHG means the total of all greenhouse gases, as converted to a common base of global warming potential, i.e., CO2 equivalent (CO2e). For tail pipe emissions, CO2 is used.

Suggested Citation:"1 Introduction." National Research Council. 2013. Transitions to Alternative Vehicles and Fuels. Washington, DC: The National Academies Press. doi: 10.17226/18264.

The 2050 petroleum reduction goal is easier to meet than the 2050 GHG goal because more options can be employed. In fact, reducing GHGs by 80 percent is likely to require reducing petroleum use by at least 80 percent. Petroleum use by the light duty fleet was 125 billion gallons gasoline in 2005 (EIA, 2011), so the targets are 62.5 billion gallons in 2030 and 25 billion in 2050.

GHG emissions from the LDV fleet in 2005 were 1,514 million metric tons of CO2 equivalent (MMTCO2e) on a well-to-wheels basis (EPA, 2012). An 80 percent reduction from that level means that whatever fleet is on the road in 2050 can be responsible for only 303 MMTCO2e/year. That is the budget within which the fleet must operate to meet the goal.

Achieving an 80 percent reduction in LDV-related emissions is only possible with a very high degree of net GHG reduction in whatever energy supply sectors are used to provide fuel for the vehicles. In short, it is not possible to greatly “de-carbonize” LDVs without greatly de-carbonizing the major energy supply sectors of the economy.

The committee determined potential costs and performance levels for the vehicle and fuel options. Because of the great uncertainty in estimating vehicle cost and performance in 2050, the committee considered two levels, midrange and optimistic. Midrange goals for cost and performance are ambitious but plausible in the committee’s opinion. Meeting this level will require successful research and development and no insurmountable barriers, such as reliance on critical materials that may not be available in sufficient quantities. The more optimistic goals are stretch goals: possible without fundamental technology breakthroughs, but requiring greater R&D and vehicle design success. All the vehicle and fuel cost and performance levels are based on what is achievable for the technology.

Other factors also will be very important in determining what is actually achieved. In particular, government policy will be necessary to help some new and initially costly technologies into the market, consumer attitudes will be critical in determining what technologies are successful, and of course, the price and availability of gasoline will be important in determining the competitiveness of alternative vehicles and fuels.


To analyze all these issues, the committee constructed and analyzed various scenarios, combining options under the midrange and optimistic cost and performance levels to see

BOX 1.1
Analytical Techniques Used in This Report

The committee relied on four models to help form its estimates of future vehicle characteristics, their penetration into the market, and the impact on petroleum consumption and GHG emissions. Chapter 2 and Appendix F describe two of the models. One is an ICEV model developed by a consultant that projects vehicle efficiency out to 2050 by focusing on reduction of energy losses, rather than the usual technique of adding efficiency technologies until the desired level is reached. The committee’s approach avoids the highly uncertain predictions of which technologies will be employed several decades from now and ensures that efficiency projections are physically achievable and that synergies between technologies are appropriately accounted for. The second is a spreadsheet model of technology costs developed by the committee, which focused on applying consistent assumptions across all of the different powertrain types. The analytical approach for both models is fully documented and the data are available in Appendix F. The methodology and results for both of these models were intensively reviewed by the committee, the committee staff, another consultant, and experts from FEV, Inc., an engineering services company. Reviewers of this report were also selected for their ability to understand this approach, which they endorsed.

The VISION and LAVE-Trans models are described in Chapter 5 and Appendix H. VISION is a standard model for analyzing transportation scenarios for fuel use and emissions. It is freely available through the U.S. Department of Energy. The committee modified it for consistency with the committee’s assumptions such as on vehicle efficiencies and usage and fuel availability. The committee carefully monitored the modifications and reviewed the results, which are consistent with other analyses.

LAVE-Trans is a new model developed by a committee member for an analysis of California’s energy future and expanded to the entire nation by the committee. It is unique among models in that it explicitly addresses market responses to factors such as vehicle cost and range, aversion to new technology, and fuel availability. It analyzes the effectiveness of policies in light of these market responses. The committee and staff spent considerable time reviewing LAVE-Trans and its results. In addition to presentations and discussions at committee meetings, one committee member and the study director spent a day going over the model with the developer and his associates. Another committee member examined intermediate calculations as well as model outputs. The results were also compared to VISION results for identical inputs and assumptions. These examinations led to recalibrations and changes in model assumptions. Reviewers of this report were also selected for their ability to understand the model, and they confirmed its validity.

Suggested Citation:"1 Introduction." National Research Council. 2013. Transitions to Alternative Vehicles and Fuels. Washington, DC: The National Academies Press. doi: 10.17226/18264.

how the petroleum and GHG reduction goals could be met. It also explored how consumers might react to new technologies. Then the committee compared the technological and economic feasibility of meeting the goals using the available options, the environmental impacts of implementing them, and changes in behavior that might be required of drivers to accommodate new technologies. Finally, the committee examined the policies that might be necessary to implement the scenarios.

Vehicle options are explored in Chapter 2 and fuels in Chapter 3. Chapter 4 discusses factors that will affect consumer choices in considering which vehicles to purchase, and Chapter 5 describes how the scenario modeling was done and the results. Box 1.1 briefly describes the models used in Chapters 2 and 5 and how they were validated.

Chapter 6 discusses policies that could enable the various options and encourage their penetration into the market as needed to implement the scenarios. Finally, Chapter 7 discusses the committee’s suggested policy options that are drawn from Chapter 6. Several current policies are encouraging actions that will reduce GHG emissions and petroleum use. The Corporate Average Fleet Economy (CAFE) standards require vehicle manufacturers to sell efficient vehicles. The Renewable Fuel Standards mandate the use of biofuels. Box 1.2 briefly describes these policies. In addition, tax credits for battery vehicles encourage consumers to buy them. Fuel taxes, carbon reduction measures such as carbon taxes, and other standards and subsidies also could be used. State and local policies may also be important, particularly in the absence of activist federal policies, but the focus of

BOX 1.2
U.S. Policies Directly Affecting Fuel Consumption

U.S. Corporate Average Fuel Economy (CAFE) Standards

From the mid-1970s through 2010, the United States had one set of standards that applied to passenger cars and another set that applied to light-duty trucks. These standards were administered by the National Highway Traffic Safety Administration (NHTSA) of the U.S. Department of Transportation, following requirements in legislation passed by the U.S. Congress in 1975. They first became effective in the 1978 model year. The standard for passenger cars that year was 18.0 miles per gallon (mpg). The standard increased to 27.5 mpg for the 1985 model year and varied between that level and 26.0 mpg from model year 1986 through model year 1989. In model year 1990 it was raised again to 27.5 mpg and remained at that level through model year 2010. The first combined light truck standard applied to model year 1985 vehicles and was set at 19.5 mpg. The light truck standard ranged between 20.0 and 20.7 mpg between model years 1986 and 1996, remained at 20.7 mpg for model years 1996 through 2004, and increased to 23.5 mpg by model year 2010.

More recently, the federal government implemented two new sets of standards. In 2010, complementary standards were set by the Environmental Protection Agency (EPA) based on greenhouse gas (GHG) emissions and by NHTSA based on fuel economy. NHTSA’s CAFE standard for 2016 was set at 34.1 mpg for cars and light trucks. In 2012, new standards were set by EPA and NHTSA through 2025, although the NHTSA standards for 2022-2025 are proposed and not yet final, pending a midterm review. NHTSA’s CAFE standard for 2025 is 48.7-49.7 mpg. If flexibilities for paying fines instead of complying, flexible fuel vehicle (FFV) credits, electric vehicle credits, and carryforward/carryback provisions are considered, NHTSA estimated that the CAFE level would be 46.2-47.4 mpg. This does not consider off-cycle credits, which could further reduce the test cycle results by up to 2-3 mpg. Thus, for comparison purposes, the committee used 46 mpg as the tailpipe mpg levels comparable to the committee’s technology analyses in Figure 2.1. Also note that on-road fuel economy will be significantly lower—the committee used a discount factor of 17 percent in assessing in-use benefits in Chapter 5. The standards are discussed in more detail in Chapter 5. In particular, see Box 5.1.

Renewable Fuel Standard

The federal Renewable Fuel Standard (RFS) was created under the Energy Policy Act of 2005 because Congress recognized “the need for a diversified portfolio of substantially increased quantities of … transportation fuels” to enhance energy independence (P.L. 109-58). The RFS was amended by the Energy Independence and Security Act (EISA) of 2007 which created what is referred to as RFS2. RFS2 mandates volumes of four categories of renewable fuels to be consumed in U.S. transportation from 2008 to 2022. The four categories are:

  • Conventional biofuels—15 billion gallons/year of ethanol derived from corn grain or other biofuels.
  • Biomass-based diesel—currently 1 billion gallons/year are required.
  • Advanced biofuels from cellulose or certain other feedstocks that can achieve a life-cycle GHG reduction of at least 50 percent.
  • Cellulosic biofuels, which are renewable fuels derived from any cellulose, hemicellulose, or lignin from renewable biomass and that can achieve a life-cycle GHG reduction threshold of at least 60 percent. In general, cellulosic biofuels also qualify as renewable fuels and advanced biofuels.
Suggested Citation:"1 Introduction." National Research Council. 2013. Transitions to Alternative Vehicles and Fuels. Washington, DC: The National Academies Press. doi: 10.17226/18264.

this report is on actions the federal government can take. Chapters 6 and 7 estimate the relative effectiveness of U.S. policies in achieving the goals of this study.

The vehicle and fuel options discussed in this report generally are more expensive and/or less convenient for consumers than those that are available now. The societal benefits they provide (in particular, lower oil consumption and GHG emissions) will not, by themselves, be sufficient to ensure rapid penetration of the new technologies into the market. Therefore strong and effective policies will be necessary to meet the goals of this study. By “strong public policies,” the committee means options such as steadily increasing fuel standards beyond those scheduled for 2025, measures to substantially limit the net GHG emissions associated with the production and consumption of LDV fuels, and large-scale support for electric vehicles or fuel cell vehicles to help them overcome their high initial cost and other consumer concerns. It also may be necessary to have policies that ensure that the fuels required by alternative powertrains are readily available.

Although the committee is generally skeptical of the value of the government picking winners and losers, the goal of drastically reducing oil use inherently entails a premise of picking a loser (oil) and developing (and perhaps promoting) winners among a set of vehicles and fuel resources.

In turn, implementation of such policies is likely to depend on a strong national imperative to reduce oil use and GHG emissions. The committee has not studied such an imperative but notes that, given the length of time needed to make major changes in the nation’s light-duty vehicle fleet, additional policies will be needed soon to meet the goals.


EIA (Energy Information Administration). 2011. Annual Energy Review 2010. Washington, D.C.: U.S. Department of Energy.

EPA (Environmental Protection Agency). 2012. Inventory of U.S. Greenhouse Gas Emissions and Sinks:1990-2010. Available at

Suggested Citation:"1 Introduction." National Research Council. 2013. Transitions to Alternative Vehicles and Fuels. Washington, DC: The National Academies Press. doi: 10.17226/18264.
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Suggested Citation:"1 Introduction." National Research Council. 2013. Transitions to Alternative Vehicles and Fuels. Washington, DC: The National Academies Press. doi: 10.17226/18264.
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Suggested Citation:"1 Introduction." National Research Council. 2013. Transitions to Alternative Vehicles and Fuels. Washington, DC: The National Academies Press. doi: 10.17226/18264.
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Suggested Citation:"1 Introduction." National Research Council. 2013. Transitions to Alternative Vehicles and Fuels. Washington, DC: The National Academies Press. doi: 10.17226/18264.
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For a century, almost all light-duty vehicles (LDVs) have been powered by internal combustion engines operating on petroleum fuels. Energy security concerns about petroleum imports and the effect of greenhouse gas (GHG) emissions on global climate are driving interest in alternatives. Transitions to Alternative Vehicles and Fuels assesses the potential for reducing petroleum consumption and GHG emissions by 80 percent across the U.S. LDV fleet by 2050, relative to 2005.

This report examines the current capability and estimated future performance and costs for each vehicle type and non-petroleum-based fuel technology as options that could significantly contribute to these goals. By analyzing scenarios that combine various fuel and vehicle pathways, the report also identifies barriers to implementation of these technologies and suggests policies to achieve the desired reductions. Several scenarios are promising, but strong, and effective policies such as research and development, subsidies, energy taxes, or regulations will be necessary to overcome barriers, such as cost and consumer choice.

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