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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
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3
Mitigation Research to Inform Policy and Practice

The mitigation strategies of primary interest to this study are opportunities to (a) reduce travel on vehicles and modes with high emissions of greenhouse gases (GHGs) and (b) shift travel to modes with lower emissions. The climate change bill that passed the House of Representatives in June 2009, the similar Senate bill proposed in October 2009 by Chairman Boxer of the Environment and Public Works Committee and Senator Kerry, and the transportation reauthorization legislation introduced by Chairman Oberstar of the Transportation and Infrastructure Committee all would require new federal, state, and regional efforts to plan for and reduce transportation GHG emissions, over and above the reductions that will come from more fuel-efficient vehicles. Moreover, reauthorization legislation introduced in the Senate by Chairman Rockefeller and Senator Lautenberg of the Commerce Committee would require reductions in per capita travel, a provision that 60 members of the House have endorsed. Many states have also committed to reducing travel. Because travel and economic growth are so tightly linked, however, an understanding of the potential impacts of such policies on economic growth as well as on GHG emissions is important. Unfortunately, little guidance about the effectiveness and costs of various transportation mitigation policies to save energy and reduce GHG emissions is available, although such information is beginning to be produced (Cambridge Systematics 2009; Center for Clean Air Policy 2009).1

1

Both of these reports appeared late in the committee’s deliberations. Information about the assumptions and methods behind the estimates in the Cambridge Systematics (2009) report, which covers a broad array of mitigation measures, was not available for review at the time of this writing.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

This chapter first provides a broad overview of strategies to make travel more energy efficient and identifies areas of uncertainty that research could address. It then indicates areas in which research is needed and describes criteria for how such research should be organized and managed.

INTRODUCTION

As an organizing scheme, it is useful to think about reducing transportation GHG emissions and energy consumption on the basis of a framework initially developed by Schipper et al. (2000) and employed by Eads (2008). The amount of CO2 emissions from fuel combustion by transport can be represented as follows:

where

G = CO2 emissions (or GHG emissions) from fuel combustion by transport,

A = total transport activity,

Si = modal structure of transport activity,

Ii = energy consumption (fuel intensity) of each transport mode, and

Fi,j = sum of GHG emissions characteristics of each transport fuel used by various modes (i = transport mode, j = fuel type).

Understanding the potential value of mitigating transportation GHG emissions and reducing energy consumption requires examination of each of these variables.

  • A = total transport activity, which is a function of growth in gross domestic product (GDP) and population. It is also influenced by development and trade patterns (which determine the distance between origins and destinations).

  • S = modal structure of transport activity. Strong growth has occurred in recent decades in aviation, in the freight mode share of trucks compared with rail and water, and in light-duty vehicle (LDV) (cars, SUVs, and pickup trucks used for personal travel) use compared with transit.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×
  • I = energy consumption or fuel intensity of modes, which has stagnated in the highway mode in the United States for the past 25 or so years, a period when fuel prices were low and policy makers were unwilling to require increases in LDV corporate average fuel economy (CAFE) standards.2

  • F = GHG emissions characteristics of modes and fuel types. Virtually all forms of U.S. transportation rely on petroleum-based fuels; thus, transportation GHG emissions are highly correlated with total fuel consumed.

Not only the amount of activity and vehicle energy intensity but also the operation, construction, and maintenance of the infrastructure itself have energy and GHG emission consequences. This chapter will focus primarily on research opportunities to affect total transport activity, mode structure, and energy consumption through changes in travel demand; the role that infrastructure construction, operations, and maintenance might play in energy and emission reductions will be touched on. A brief overview of vehicle fuel intensity and emissions characteristics is also provided to help place these topics in perspective.

TRANSPORTATION ACTIVITY

Total transportation activity is closely related to the national economy, population change, and development patterns. Although legislative goals call for reductions in energy consumption and GHG emissions from transportation, most projections assume that U.S. passenger and freight travel will increase as the economy, population, and built environment expand.3 The section that follows gives an overview of the influences of population and economic growth and changes in urban form on travel

2

The latter has changed with the passage in 2007 of sharply increased CAFE standards, which are intended to improve LDV new fleet fuel economy to 35 mpg by 2020, and with the announcement of the Obama administration in May 2009 that it would accelerate achievement of these standards to 2016.

3

See, for example, the Department of Energy’s Annual Energy Outlook 2009, whose forecast of a 10 percent increase in transportation energy consumption over current levels by 2030 is based on assumptions about economic and population growth. http://www.eia.doe.gov/oiaf/aeo/, accessed July 7, 2009.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

demand. This is followed by a description of a broad set of options for moderating growth in travel and of the gaps in knowledge about how well such strategies might perform.

Background

Transportation both contributes to economic growth and is influenced by GDP as incomes rise (Eads 2008). The relationship between per capita real income and per capita travel can be expected to change as advanced industrialized nations shift to service economies. As a general rule, however, per capita real incomes are highest in nations with the most per capita travel (e.g., in North America) (Eads 2008, 219). One obvious way to reduce transport GHG emissions is to reduce travel or at least the rate of growth in vehicle miles of travel (VMT), but care must be taken in doing so to avoid harming economic activity. The American Association of State Highway and Transportation Officials has indicated that the highway system cannot manage more than 1 percent annual growth in VMT over the next two or three decades because of expected limited capacity growth; hence, efforts to moderate VMT growth may be necessary for reasons other than GHG mitigation, especially congestion management. Environmental advocates go a step further, seeking actual reductions in VMT through increases in the cost of travel and changes in urban form, which are discussed below.

Population growth will increase total transportation activity. The U.S. Census Bureau projects that population will grow between 0.8 and 1 percent annually from 2008 to 2050, which will result in a 56 percent increase over 2008 and a net increase in population of 135 million (U.S. Census Bureau 2009, Table 3). Thus, all other things being equal, one could expect total U.S. passenger travel to increase simply because of population growth by 2050. Indeed, in past decades VMT has increased much faster than population, presumably because of rising incomes (Memmott 2007).

Future travel will be affected not only by the nature of future development but also by the existing built environment, which changes slowly. Trends within and across most metropolitan areas in recent decades have generally been toward less densely developed areas. The United States is increasingly “urbanized” according to official statistics, but “suburbanized”

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

would be a better descriptor given that the formal Census Bureau definition of “urban” is areas with at least 1,000 population per square mile, which is a low threshold for development density—about 1.6 people per acre or about 0.67 houses per acre at average household occupancy rates. Under this definition, metropolitan areas are continuing to suburbanize. From 1970 to 2000, the suburban population slightly more than doubled from 52.7 million to 113 million. This growth occurred mainly at the expense of nonmetropolitan areas; population in central cities grew, but only by about 55 percent, from 44 million to 68.5 million (Giuliano et al. 2008). In terms of relative share, suburban population increased from 54.5 percent of total metropolitan population in 1970 to more than 62 percent in 2000. As of 2000, 80 percent of the total U.S. population lived in metropolitan areas, and 50 percent resided in the suburbs of these areas. As origins and destinations become farther apart, travel distances necessarily increase. Obviously, trips are shorter and more are made by transit, walking, or biking in dense urban environments such as Manhattan or central Boston than in the suburbs or exurbs of metropolitan areas or in rural areas, but the trend in preceding decades has been toward suburban development. The trend could change with changes in preferences and public policy. The ever-growing share of population growth represented by immigration and the aging of the baby boom cohort could alter preferences for suburban living (TRB 2009). Research to examine such changes and inform public policy is suggested later in this chapter.

The United States has a large supply of inexpensive land, and vast distances separate population and economic centers, which depend on transportation connections. The nation’s extensive highway system, the success of motor carriers in using this ubiquitous system to capture mode share, and the aviation system have allowed economic development to spread across the nation. The locations of major centers of trade and economic activity are no longer constrained by the requirement of proximity to a water port or adjacency to a railroad. The large supply of inexpensive land means that, without changes in land use policies, even high energy prices may not discourage the location of economic activity in low-density areas, simply because the costs of development are so low in comparison. This pattern of national economic development has

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

allowed formerly less developed regions to become more prosperous but has increased the demand for transportation.

If reducing total travel, or at least the growth rate of travel, becomes a policy objective for the nation, an understanding of the feasible and acceptable options for reducing travel in the most efficient ways become important. Clearly, successful implementation of policies requires that they be acceptable to a significant proportion of the public. Some broad options for addressing travel growth as well as suggestions for research areas to reduce knowledge gaps are outlined below.

Options for Reducing Total Transportation Activity and Associated Research Needs

In this section broad strategies to reduce total demand for transportation are reviewed. Demand would be reduced by raising the cost of travel through higher fuel taxes or pricing use of the transportation system, by changes in land use to make travel more efficient, and by use of telecommunications technology to substitute for travel. A subsequent section of this chapter discusses strategies to influence travelers to shift to more fuel-efficient modes.

Reduce Motorized Vehicle Use by Raising the Cost of Fuel

Imposition of carbon taxes, or increasing the cost of fuels indirectly through a carbon cap-and-trade regime, will reduce travel by making fuel more expensive. Available analysis indicates that LDV demand is fairly insensitive to increases in fuel cost, however (Small and Van Dender 2007). In the short run higher prices do not appear to reduce travel much, and in the long run consumers shift to more fuel-efficient vehicles. Carbon taxes or cap-and-trade proposals that would raise fuel prices, of the type debated in the U.S. Senate in 2008, would have minor effects on total fuel purchases and VMT in part because the impact of such proposals on fuel prices would be modest and in part because the increases in fleet fuel economy standards that Congress enacted will significantly reduce future travel costs (CBO 2008). Another reason for the limited response is that small and mobile transportation vehicles depend on fuel with high energy density, which is not the case for fixed energy users such as power plants. The latter energy users have more substitute

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

fuels at their disposal and, therefore, more cost-effective options for reducing GHG emissions.

Some argue that transportation should reduce its GHG emissions in proportion to its share of total GHG emissions. Others argue that this should not be a concern as long as emission reductions are taking place in the economy through the most cost-effective responses. Indeed, for reasons explained above it is likely that carbon pricing schemes (tax or a carbon cap-and-trade system) will not exert a proportional effect on transportation even if carbon prices are set to reflect the external cost of carbon emissions, including climate-related costs. Nevertheless, policy makers may be motivated to reduce energy use in transportation for other reasons. For example, concern about imports of petroleum, often from unstable parts of the world, also motivates interest in measures to reduce transportation petroleum consumption, including measures aimed at reducing VMT.

If policy makers wish to reduce total transportation demand beyond the levels that would be achieved through a carbon tax or cap-and-trade regime, questions arise concerning how much travel can be reduced and at what cost. It is largely unknown how much total personal and freight travel could be reduced, independent of changes in development and logistic patterns, without risking a reduction in GDP that is greater than the societal benefits from these actions. Clearly, some trip making is not highly valued by users but imposes higher social and environmental costs than the user is required to pay. Ideally, such travel would be the first to be reduced by pricing and other measures aimed at reducing overall VMT. Whereas people and shippers would not make or pay for trips if they did not value the end result more than the cost of the trip, it is important to ensure that they pay all of the costs.

As policy makers consider proposals that would reduce both personal and freight VMT, they need information about how changes in travel affect productivity and economic growth. A fundamental problem facing all proposals to reduce VMT is a lack of understanding about how they would affect travel behavior and the economy. Little research is supported in this area through federal programs; hence, the knowledge base is limited. This topic is further discussed in the research recommendations below.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×
Price Use of Transport Infrastructure

Pricing strategies (congestion pricing, areawide pricing, parking, tolling, or charging for mileage traveled), while controversial, could reduce total automobile travel by causing some trips to be forgone and by encouraging mode shift. Strategies for pricing highway transportation would probably be the most effective in reducing automobile travel and encouraging mode shifts (discussed separately below), although congestion pricing may mostly serve to shift travel to less congested times and places rather than to reduce trips.4 These proposals are efficient in the sense that the affected parties decide on how best to respond.

The Federal Highway Administration (FHWA) Value Pricing Program has been funding research and experimentation at the regional level on a variety of approaches such as pricing high-occupancy vehicle lanes, parking pricing, and cashing out parking. Experimentation has demonstrated the effect of pricing strategies on traffic flow, but much remains to be understood about public acceptability, equity, environmental impacts, and the appropriate institutional arrangements for carrying out pricing programs (Bhatt et al. 2008). Road pricing has been tested and implemented on a broader scale in Europe, but whether the positive experiences in London and Stockholm would translate to the United States remains uncertain (Richardson and Bae 2008, 9). There is as much need to learn about whether and how pricing strategies can be made more palatable, perhaps through strategies based on how revenues are allocated, as there is to learn what effects such strategies have on demand and GHG emissions. An understanding of the potential cost per ton of GHG emission reduction under the full range of pricing strategies is also needed.

Interest in moving away from fuel taxes as the main revenue source for transportation trust funds to a charge on motorists for mileage traveled is growing. With such a system, the mileage rate charged could be

4

The trial imposition of congestion fees in central Stockholm during 2006, for example, reduced total work and school trips by automobile into the central area, but virtually all these work trips shifted to transit (Eliasson et al. 2009, 245). In contrast, peak-period discretionary automobile trips (equal in number to work and school trips) made before the imposition of the charge did not shift to transit. The study was unable to determine whether the trips were canceled, delayed, substituted for, or combined with other trips.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

adjusted to reflect environmental values. For example, some mileage charging approaches would permit supplemental charges based on vehicle fuel economy. If such a regime could result in a systemwide approach to charging for road use, road pricing across all road classes would be technically feasible. Appendix A describes research and demonstration programs that would test alternative mileage charging technologies and engage the public and key stakeholders in a process to determine the acceptability of such an approach.

Change Urban Development Patterns

The National Research Council (NRC) committee that produced estimates of GHG reduction and energy savings that would be achieved by a doubling of the residential density of 25 to 75 percent of future residential development by 2050 indicates that the effects will be modest (TRB 2009). The scenarios in that report indicate that such changes could result in reductions in VMT, energy consumption, and CO2 emissions ranging from less than 1 to 11 percent by 2050, although the committee disagreed about the plausibility of achieving a doubling of density for 75 percent of future development.

Policy makers wishing to achieve decreases in VMT through urban form and transit investment strategies need to know much more about the ingredients necessary for success of such strategies and what their benefits and costs might be. Research has shown that a blend of regulation, design, and investment in alternative modes is necessary for achievement of successful compact, mixed-use development, but which elements are necessary and to what degree, and how they vary across different urban forms, are unknown. Successful smart growth has included allowance for mixed uses (stores, offices, and housing located together rather than separated), investments in improved transit accessibility, better physical design to encourage and support walking, and parking pricing and changes in zoning to constrain maximum parking rather than mandate minimum parking. What is not well understood is the precise formula, how it might apply in different metropolitan areas, or what it would cost. There are very considerable differences in how metropolitan areas are developing (Lee 2007; Giuliano et al. 2008). Atlanta’s urban form, which is typical of fast-growing, sprawling metropolitan areas in

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

the South, differs from that of areas such as New York City, Boston, Chicago, or even San Francisco and Los Angeles. Transit-supportive strategies for compact development that work well for older cities with central business districts built up before the automobile or constrained from expanding by topography would not necessarily be appropriate for Atlanta or Houston.

Research to address such questions would focus on detailed case studies of successes and failures of explicit transportation–land use strategies. A complete scholarly analysis of the successes that Portland, Oregon, has achieved would be especially valuable. Portland’s success has apparently been the result of several factors: strong state leadership, state growth management policies with an urban growth boundary as part of these policies, a regional government with strong influence over municipal land use and transit planning and investment, a young workforce with a fast-growing high-tech industry, political consensus on growth policy, and others. Insight into the measures needed to replicate Portland’s experience elsewhere would be useful to policy makers. To the extent that the measures used in Portland have been applied elsewhere, it would be valuable to know whether they succeeded or failed, and why.

Better tools are also needed by metropolitan planning organizations (MPOs) to analyze transportation and land use options for regional policy makers. [This is in large part a demonstration and technology transfer problem; sophisticated linked travel and land use models are employed in a few places, but they are not employed by many MPOs (TRB 2007).] TRB’s 2007 study on travel model practice in MPOs recommended research, technology demonstrations, and technology transfer to improve modeling and the state of practice. Such model improvements will become essential if states and regions must analyze the effects of various taxes, fees, regulations, and other policies on travel.

At a more fundamental level, MPOs need much better models to capture behavioral responses. Models of trip generation need to become much more sensitive to how people change their trip making as circumstances change. In turn, development of such models requires more fundamental research into travel behavior (described later in this chapter). Models of intrametropolitan area freight travel and the data on which they are based are even less well developed.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

Many advocates of smart growth believe that this form of development has many ancillary benefits—closer community ties, more affordable housing, healthier lifestyles, and so forth. Whether the changes would all be beneficial is uncertain since families would also be giving up some of the housing size, privacy, and open space that come with low-density development. A way to measure (better than do stated preference surveys) how different physical environments, including different transportation infrastructure and operations, affect well-being is needed. Analysis of the cost per ton of GHG emissions reduced by smart growth development should be accompanied by estimates of the other social and economic benefits and costs of this form of development.

As a general rule, little is understood concerning what might be thought of as “second-order” effects that might result from more efficient transportation and development. Would the coupling of such outcomes have significant multiplier effects?

Use Technology to Substitute for Trips

Telecommuting, videoconferencing, Internet shopping, and the widespread availability of information and communications technologies (ICTs) all appear to have the potential to substitute for or reduce travel. The relationships between travel and ICTs are more complex than is commonly assumed; there are as many arguments for how ICTs stimulate additional travel as for how ICTs reduce it (Mokhtarian 2009). Research has not provided any empirical evidence that telecommunications, on a net basis, substitute for private vehicle trips (Choo et al. 2007), although there is evidence of a modest impact in telecommuting (Choo et al. 2005). Good evidence of how ICTs affect total travel or whether they stimulate or substitute for travel is not yet available. Development of research methods is needed in this area, along with better understanding of how information and communications can substitute for trips. The need for such knowledge confirms the importance of the fundamental research program recommended later in this chapter.

Summary

Strategies are available that would affect demand in ways that could help achieve energy and climate goals efficiently, but understanding of their

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

costs and benefits is highly conceptual. Much remains to be known, and state and regional decision makers will need a high degree of specificity to ensure that these strategies are cost-effective, feasible, and acceptable.

MODAL STRUCTURE AND ENERGY INTENSITY

Modal structure and modal energy intensity are considered together in this section because most of the relevant policy questions raised by climate change and energy conservation goals concern opportunities to shift trips from modes with higher to those with lower energy intensity. Shifting modal preferences could affect transportation GHG emissions, depending on the nature and magnitude of the shift. As Table 3-1 indicates, the highest energy-consuming modes are highway LDVs, freight trucks, and aviation, which collectively account for 86 percent of transportation energy and 84 percent of transportation GHG emissions.

The energy and GHG emission reduction benefits of shifting from automobile to transit bus, from automobile to intercity rail, or from aviation to intercity rail may not be as great as commonly assumed. For example, according to federal statistics, automobiles, on average, require energy per passenger mile comparable with that of bus transit (possibly even less according to some estimates) and only 26 percent more energy per passenger mile than rail transit (Table 3-1).5 Such comparisons, however, are notoriously difficult because of data problems, the distortions of comparing averages, and the importance of including life-cycle energy and emissions in the calculations.6 During the peak period when transit buses are full, for example, transit bus energy efficiency outperforms other passenger modes, but the off-peak performance of transit buses is

5

Energy intensity estimates for transit bus differ across sources. In the Transportation Energy Data Book, 28th edition, the value of 4,253 Btu per passenger mile is given for 2006, but in National Transportation Statistics, the most recent value estimated is 3,262 for the same year (see http://www.bts.gov/publications/national_transportation_statistics/, accessed April 12, 2009). Furthermore, Btu per passenger mile for automobiles has been falling for decades, a trend that will continue given CAFE standards adopted in 2007; the energy consumed per passenger mile for bus transit has been rising over the same period (see Transportation Energy Data Book, 28th edition, Table 2.13).

6

Estimates of transportation life-cycle energy and emissions attempt to include all sources of energy required for manufacturing, operating, and recycling vehicles as well as for constructing and operating their required infrastructure.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

TABLE 3-1 Energy Intensity and CO2 Emissions by Mode

 

Btu 2007a (trillions)

Percent

Btu/Passenger Mile,b 2006

Btu/Ton-Milec

Modal CO2d (percent)

Highway

22,293

80.0

 

 

78.9

Light vehicles

16,925

60.4

 

 

60.1

Car

9,218

32.9

3,510

 

34.2

Light truck

7,676

27.4

 

 

25.8

Motorcycle

30

0.1

 

 

0.1

Buses

194

0.7

3,262e–4,259

 

0.5

Transit

91

0.3

 

 

 

Intercity

30

0.1

 

 

 

School

73

0.3

 

 

 

Medium or heavy trucks

5,274

18.8

 

~3,000–4,000f

18.4

Nonhighway

5,609

20.0

 

 

 

Air

2,509

9.0

 

 

 

General aviation

244

0.9

 

 

0.6

Domestic air carrier

1,847

6.6

3,250

 

6.6

International carrier

419

1.5

 

 

 

Water

1,559

5.6

 

304

4.4

Domestic freight

1,312

4.7

 

571

 

Recreational

247

0.9

 

 

 

Pipeline

883

3.2

 

 

1.9

Rail

657

2.3

 

330

2.3

Freight

570

2.0

 

 

 

Passenger

90

0.3

 

 

 

Transit

47

0.2

2,707

 

 

Commuter

29

0.1

2,527

 

 

Intercity

14

0.1

2,650

 

 

Total

28,002

100

 

 

 

aDavis et al. 2009, Table 2.6.

bDavis et al. 2009, Tables 2.13, 2.14.

cDavis et al. 2009, Table 2.16.

dEads 2008, Table B-2.

eNational Transportation Statistics (http://www.bts.gov/publications/national_transportation_statistics), Table 4-20.

fDavis et al. (2009) no longer provide energy intensity estimates for intercity trucks because of the difficulties of arriving at accurate estimates. The figures shown were calculated by using 2005 data as the most recent available. Btu’s are from Davis et al., Table 2.16; ton-miles are from Pocket Guide to Transportation 2008, Table 4-4, Bureau of Transportation Statistics, U.S. Department of Transportation. However, more careful comparisons between truck and rail energy intensity for moving comparable loads over comparable distances find much smaller differences than the more than 10:1 or 12:1 ratio shown above. Babcock and Bunch (2007), for example, estimate a ratio of only 3:1 for comparable agricultural commodities.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

the worst of the passenger modes (Chester and Horvath 2008). The energy required per passenger mile for aviation is about a quarter greater than that required for intercity rail (Table 3-1), but the net increase depends on several factors, including the distance over which trips are taken and the estimated market share of air and rail. Aviation is less efficient for shorter and more efficient for longer distances. [One comparison of the ability of high-speed rail to reduce aviation CO2 emissions in short-haul markets (less than 620 miles) finds a reduction of less than 1 percent in aviation emissions if high-speed rail gained 30 percent of intercity passenger market share in these markets by 2030 (Jamin et al. 2004).] Whether the energy required for constructing new rail lines offsets energy advantages is also an important consideration.7 These overall averages, however, tend to mask the outcomes in particular markets and appear to be highly dependent on load factors and methods. Previous attempts to compare intercity passenger modes on a full cost basis have shown aviation to be superior to rail and highway, although the analysis is highly dependent on which costs and benefits are included and how they are monetized (Levinson 1996). These examples highlight some of the counterintuitive outcomes in transportation and emphasize the importance of sound research that leads to good policy choices.

Freight

Mode shifts appear to be particularly relevant in freight, because trucking is the most energy-intensive freight mode and has a large and growing share of ton-miles. Trucking market share and total ton-miles have grown rapidly since deregulation of the surface modes in the 1980s; trucking’s share of ton-miles increased from 19 to 29 percent between 1980 and 2005 (Table 3-2). Rail ton-miles have also been growing, but not as sharply, while domestic water transportation has been steadily declining in market share and ton-miles. International freight move-

7

Whether rail or aviation is less energy intensive depends to a large extent on estimated load factors. Projections of load factors, however, have a poor track record. See Energy and Emissions in Transportation: How Mikhail Chester Makes it Easier to Be Green, NewsBITS, Vol. 4, No. 1, Fall 2008 (http://www.sustainable-transportation.com/), accessed April 13, 2009. The relative impact of the two modes on GHG emissions also depends on questions concerning the radiative forcing effects of aircraft contrails.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

TABLE 3-2 U.S. Domestic Freight Ton-Miles, 1980–2005

 

Truck

Rail

Water

Pipeline

Total

Trillions of ton-miles

 

 

 

 

 

1980

0.63

0.93

0.92

0.92

3.4

1985

0.72

0.88

0.89

0.82

3.31

1990

0.85

1.06

0.83

0.86

3.6

1995

1.03

1.32

0.81

0.93

4.09

2000

1.19

1.55

0.65

0.93

4.32

2005

1.29

1.73

0.59

0.9

4.51

Percentage change, 1980–2005

105

86

−36

−233

 

Market share (%)

 

 

 

 

 

1980

19

27

27

27

100

1985

22

27

27

25

100

1990

24

29

23

24

100

1995

25

32

20

23

100

2000

28

36

15

22

100

2005

29

38

13

20

100

Percentage change, 1980–2005

54

40

−52

−26

 

SOURCE: BTS 2007, Figure 4.

ments, mostly by water, have been growing strongly, but there are no practical substitutes for most commodities moved across oceans, and GHG emissions per ton-mile for freight transported by oceangoing vessels are the lowest of all modes. Air freight has been growing faster than other modes, but domestic air freight ton-miles represent far less than 1 percent of the total (BTS 2007). Policy makers could benefit from better insight into the potential of policies that would shift freight from truck to rail or water. Because freight markets are highly competitive, commercial travel should be energy efficient, but there are market distortions, such as direct and indirect subsidies to different modes, inadequate competition in some corridors, and institutional barriers. Among the institutional barriers are budgetary impediments to investment of waterway trust fund revenues for improving channels and locks and for dredging harbors. The kinds of freight and the market distances that are candidates for diversion from truck to rail, and the costs and benefits of shifting modes, would be useful information.

National policy makers should have a better ability to weigh policy choices that would affect modal demand in order to understand their

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net benefits from environmental, economic, and safety perspectives. Available data on the energy intensity of various freight modes suggest that generalizations about the benefits of shifting modes are inadequate. Opportunities for improved energy efficiency per ton-mile depend on particular corridors and markets (Winebrake et al. forthcoming); understanding which corridors and markets would require better data on freight origin-to-destination (O-D) flows, econometric studies of potential freight mode shifts, and better insight into logistics patterns.

Most studies only compare GHGs per ton-mile emitted by the various modes; this metric shows water and rail to be vastly better than truck. Rail and water rates are also typically well below those of trucks. Commodities in shipment, however, carry inventory costs to shippers. Hence, shippers of high-value cargoes are usually willing to pay a premium to have goods moved by truck, which is the fastest mode for most domestic shipments of less than 1,000 miles. Delaying these shipments by moving them on slower modes also implies increased cost to the national economy: even though water or rail freight rates may be lower, consumers would have to pay for the extra inventory costs of goods that move more slowly.8

To appreciate the overall social benefit of policies to encourage mode shift, better quantification of the full external costs and benefits of the various modes is needed. This requires an understanding of the nature of existing subsidies and policies for reducing undesirable ones. The 1996 study Paying Our Way: Estimating Marginal Social Costs of Freight Transportation laid out a methodology by which the social costs and benefits of various freight modes could be compared on an O-D basis (TRB 1996). The collection of data and the analysis of a sample of freight O-D movements large enough to provide a better sense of the comparative social and environmental costs of the modes are still needed.

Passenger

Intercity

As Table 3-3 indicates, aviation and personal vehicles dominate trips of 100 miles or more; they account for about 96 percent of these passenger

8

These modal comparisons are simplified to make a point. In fact, many long-distance freight movements (1,000 miles or more) rely on multiple modes, typically truck and rail.

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TABLE 3-3 Long-Distance Passenger Travel in the United States by Mode, 2001

 

Person Miles (percent)

Personal use vehicle

55.9

Commercial airplane

40.5

Bus

2.0

Train

0.8

Other

0.9

NOTE: “Long distance” for these data means round-trips to a destination at least 50 miles away.

SOURCE: National Transportation Statistics (http://www.bts.gov/publications/national_transportation_statistics), Table 1-39.

miles. Passenger rail currently accounts for less than 1 percent of such travel. Carbon taxes or cap-and-trade policies could affect total intercity trips and mode share, but the magnitude of the benefits is unclear. Amtrak currently operates at about 50 percent of capacity nationwide (Polzin 2008), so ridership could be doubled at low cost. Given the small market share, that would have little impact on national transportation energy consumption or GHG emissions. Furthermore, in many city-pair markets, air travel tickets (whose prices do not include external costs) are less expensive and door-to-door travel by air is faster. Road pricing could affect mode shift and make air and rail more cost-competitive, but the potential magnitude of the shift and how much difference it might make are uncertain. For example, for family vacation trips and many short business trips involving more than one person, the efficiencies of having a vehicle at the destination must be considered, particularly when the destination does not have a good transit system.

Short-Distance Travel

Opportunities exist for mode shift in personal short-distance travel. As Table 3-4 indicates, the automobile, which accounts for about 86 percent of trips, is by far the dominant mode for all short-distance personal trip purposes, followed by walking (8.6 percent), other (3.4 percent), and transit (1.6 percent). These mode shares reflect all person trips (urban, suburban, and rural). At the urban scale, transit has a larger share of trips, and because origins and destinations are closer together, other modes are

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TABLE 3-4 Percentage of Total Person Trips by Mode and Trip Purpose, 2001

 

Total

Work Commute

Work Related

Family, Personal

School, Church

Social, Recreational

Other

Private

86.3

92.4

91.2

90.9

71.3

80.7

67.2

Public transit

1.6

3.7

1.8

1.1

2.1

1.0

4.2

Walk

8.6

2.8

4.2

7.1

9.6

14.5

15.9

Other

3.4

1.0

2.7

0.9

16.9

3.7

12.3

Total

100

100

100

100

100

100

100

SOURCE: Hu and Reuscher 2004.

more competitive with personal vehicles. There are also opportunities to improve LDV passenger mile efficiency; the average LDV trip has a vehicle occupancy rate of 1.63 persons (Hu and Reuscher 2004), indicating considerable spare capacity and opportunity for ridesharing, which would be encouraged by carbon taxes, carbon cap-and-trade proposals, and pricing.

Improved Modal Efficiency

Modal fuel intensity and associated GHG emissions could be decreased by reducing congestion, smoothing traffic flow, and curtailing hard accelerations and high speeds. The benefits for highway transportation energy conservation could be important. Barth and Boriboonsomsin (2008), for example, estimate that applying these measures to Southern California highways could reduce the GHG emissions of such travel by up to 20 percent, although the degree of regulation required to achieve such efficiencies exceeds current policy and practice. Research may identify tangible benefits from operational strategies that are less controversial than automated speed enforcement. Some of this work is already under way at the U.S. Department of Transportation through the Intelligent Transportation Systems Program and FHWA’s Operations R&D and program efforts; estimates of the energy-saving and GHG-reducing benefits of such strategies would be helpful to decision makers.

Life-Cycle Analysis

As already mentioned, accuracy requires that modal strategies be compared on a full life-cycle basis. For example, Lave (1977) pointed out that

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

an enormous amount of energy is required to build subway systems; it is difficult to repay these energy costs from the subsequent energy savings per passenger mile unless ridership levels are high. Valuable research in this area is already under way (Chester and Horvath 2008), but future policy making would benefit from additional scholarship. A related issue requiring additional study is how the increased density of development that rail systems permit becomes translated into residential and commercial building energy savings.9

ENERGY CONSUMPTION (FUEL INTENSITY)

National policy makers have long relied on vehicle and fuel regulation to meet national clean air goals, and they are likely to place similar emphasis on vehicles and fuels to meet GHG emission reduction goals. Indeed, technology and alternative fuels are likely to be the largest sources of future reductions in transportation GHG emissions. Because LDVs account for the single largest share of energy consumption among transportation vehicles (about 60 percent) and are believed to be the most mutable, most past and current analysis focuses on this vehicle category. Whether technology and fuel strategies alone will be sufficient in meeting national goals once they are set, however, is a matter of ongoing debate and analysis.

A number of recent studies have illustrated the potential role of vehicle technologies and alternative fuels in reducing LDV energy consumption and emissions. Most use some form of scenario analysis that depends on making assumptions about technology development, cost, and market penetration. Analyses that have attempted to estimate the ability of new technologies and fuels to win market acceptance and be more or less cost competitive with the current gasoline-consuming fleet have shown that the growth of fuel consumption can be significantly reduced in the 2025 to 2035 time frame, despite growth in population and VMT (Eads 2008; Heywood et al. 2008; Plotkin and Singh 2009; Lutsey and Sperling 2009). Analyses that extend projections to 2050 indicate that the new technologies

9

For example, the recent NRC report Driving and the Built Environment: The Effects of Compact Development on Motorized Travel, Energy Use, and CO2Emissions estimates that the residential building energy savings of compact, mixed-use development rival those of reduced VMT (TRB 2009).

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and fuels can reduce LDV energy consumption to 1990 or 2000 levels by that time (Eads 2008; Plotkin and Singh 2009; Lutsey and Sperling 2009). However, the scenarios imply that CAFE and market forces would not accomplish anywhere near enough GHG emission reductions if policy makers decide that transportation GHG emission levels must be reduced to 60 to 80 percent below 2005 levels by 2050. If these scenarios prove reliable, nonvehicle and fuel-based strategies will be important in meeting such a reduction goal, but whether and how they can do so are open questions.

A recent scenario for an aggressive hydrogen and transportation fuel cell–based strategy developed by a National Academies committee suggests that gasoline could be largely replaced by hydrogen for the LDV fleet by 2050 and that LDVs could meet an 80 percent GHG emission reduction target by that time (NRC 2008). The scenario was not a description of what might or is likely to happen; instead, it was a description of what could happen if adequate resources and national attention were focused in this area. The analysis indicates that even if an adequate national commitment were made, scale economies and technological breakthroughs would not make hydrogen fuel cell vehicles cost-competitive with conventional technologies until the mid-2020s. Up until that time, there would be an implicit public-sector subsidy of about $10,000 per vehicle.10 Reaching the GHG emission reduction goal would depend on many technological advances, including success in sequestering the CO2 that would be emitted to refine hydrogen from natural gas, coal, and other fuels.

Even experts engage in considerable speculation in attempting to describe how technologies might mature and markets evolve over a four-decade period. However, the different outcomes that analyses such as those above suggest illustrate the importance of ongoing and improved research to guide public policy. Technologies should be monitored as they emerge and their direct and indirect costs and benefits estimated. Projections should be updated and policy makers provided with insight into regulatory or other means of enhancing GHG emission reductions, along with estimates of the costs per ton of emissions reduced. Such studies

10

The subsidy would largely take the form of substantial public-sector investments in technology development. The production of hydrogen would also be subsidized.

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need to become increasingly integrated across all the interacting technical areas.

How consumer preferences for vehicle attributes might change is also important to understand. Although the fuel economy of LDVs remained static in the United States for about 25 years, the performance of vehicles (acceleration, safety, electronic devices) improved dramatically during that period. GHG emission reductions from vehicles and fuels would be more readily achievable if consumers became content with a static level of vehicle performance and amenities. Addressing consumer preferences on this matter would be an important line of research.

RECOMMENDED TOPICS

This section further describes the kinds of research needed. The committee agrees with many of the research areas that Burbank (2009) describes, but it has organized some of these topics under different headings and includes research topics that she did not cover. The first section below describes research and information dissemination meant to educate policy makers and practitioners about available policy options and to provide practitioners with tools and information useful in developing and implementing new programs. The second describes a fundamental research program that would, over time, improve knowledge in all the relevant areas described in the previous section.

Policy Guidance and Outreach

What Burbank (2009) refers to as “foundational” research might also be described as the development of expert syntheses of existing information into guidance for policy makers, practitioners, and researchers. These individual projects can be thought of as building blocks for subsequent policy decisions based on the best available information and as guides to subsequent research, analysis, and data collection. The scale and magnitude of the challenge of reducing transportation GHG emissions and the long time dimensions involved in climate change indicate the importance of beginning to take sensible actions now and continuing to improve the knowledge base that will be needed in coming decades. This section describes R&D to develop policy guidance and to disseminate

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

this information to policy makers at all levels. The next section describes a fundamental research program that would improve this guidance as new insights and information become available.

Policy Guidance Topics

A set of projects that would be conducted over the first few years of the program to develop specific guidance for policy makers and practitioners is described below.


Life-Cycle GHGs To a large extent, GHG mitigation focuses on opportunities to reduce automobile trips and shift travel to modes that emit less GHGs per passenger mile or ton-mile. An understanding of the full life-cycle GHG emissions associated with each mode is important in developing policy for mode shift. Life-cycle GHG emissions include those associated with the extraction, refinement or production, delivery, and consumption of fuel used by various modes; the construction of vehicles; the construction and operation of infrastructure; and the disposition or recycling of vehicles that have ended their useful life span. Extensive representations of emissions associated with vehicles, fuels, and modal alternatives are included in Delucchi’s life-cycle emissions model, but it has fairly simple representations of the emissions associated with infrastructure construction and operations (Delucchi 2003). Valuable research is being done in this area (see, for example, Chester and Horvath 2008), but additional research is needed to build a robust foundation for policy analysis. This project would define the state of the art, provide the best available estimates to policy makers, and recommend research needed to improve understanding.


Cost-Effectiveness, Including Co-Benefits and Costs The goal of analysis in this context is to provide policy makers with the best possible information about effectiveness and cost per ton of GHG reduced by individual and collective strategies. Some work has been done on the cost-effectiveness of certain strategies, particularly in the vehicles and fuels area (Lutsey and Sperling 2009), but in many other areas considerable gaps remain to be filled to guide policy decisions. Many strategies are believed by their supporters to have benefits other than GHG emission reduction that society also values. They may also have costs that are not obvious. Typically,

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cost-effectiveness analysis is limited to a comparison of implementation costs to achieve a desired outcome and does not consider the full range of costs and benefits. This research project would provide the best available estimates of cost-effectiveness of individual strategies, which would necessarily draw on the life-cycle estimates described above, and would include estimates of co-benefits and costs. It is not assumed that all costs and benefits can be monetized, and therefore a full benefit–cost analysis is not practical. However, cost-effectiveness analyses alone provide incomplete information for policy makers. Implementation of various strategies typically requires trade-offs among valued goods and preferences, which policy analysis should also illuminate. Areas of uncertainty might mean that this guidance would be partial and incomplete, which would lead to the identification of gaps in knowledge that future research could fill.


Low-Hanging Fruit Burbank (2009) describes these as opportunities to reduce GHG emissions with “no regrets.” This project would review the full range of possible transportation strategies to identify those that might be implemented in the near term, estimate their potential for reducing GHG emissions, identify barriers to implementation, and provide recommendations for overcoming the barriers.


Land Use and VMT This area of research has been the most influenced by value preferences, perhaps because most proposals for reducing travel associated with land use patterns involve changes in norms for housing style and location and personal vehicle use that have prevailed for decades. Special Report 298 (TRB 2009) summarizes the knowledge base concerning the relationships among development patterns, VMT, energy use, and GHG emissions. Most studies have been unable to control for the many influences on the built environment and travel behavior (TRB 2009). The most rigorous studies imply that more compact, mixed-use development, coupled with good transit accessibility and policies to make automobile use less attractive, will reduce future automobile use modestly by 2030 and 2050 (TRB 2009).11 The magnitude of

11

The committee that prepared Special Report 298 focused on estimating the impact that compact, mixed-use development would have on automotive VMT. It explicitly did not review the full benefits and costs of compact, mixed-use development.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

the effect, however, will vary with local contexts, making generalizations about benefits and costs unreliable. Advancing society’s collective understanding of these issues depends as much on the process for conducting credible research as it does on the results. Recommended is a project to (a) develop a process for involving expert stakeholders with different world views and perspectives in the design of future research and (b) conduct research to provide the most scientific approach possible to sorting out this complex, multifaceted topic. The land use–transportation area is value laden and difficult to research well because of the many policies, practices, and preferences that influence how areas develop and the long time periods involved in shaping the built environment. These characteristics make the research area something of a special case. It should be overseen by the diverse stakeholders mentioned above, and the research that is conducted should focus on fundamental issues about which reasonable people disagree. The research should be designed by professionals to ensure that it is well conceived and of the highest scientific rigor.


National and Local Data Gaps The transportation field suffers from poor and inadequate data. Much of the good behaviorally oriented research that occurs today is based on unique or locally specific data sets, from which it is difficult to generalize. Transportation policy, however, is made at all levels of government—federal, state, regional, and local—and the kinds of policies considered appropriate are often determined by geography, local political preferences, and institutional capabilities. Hence, passenger data are needed at different spatial scales and time periods, for which there are many gaps. Freight data are even less available than passenger data, in part because of the proprietary nature of much of the information. (Ways of dealing with this problem have been addressed in the freight rail area.) This project would define the key data about passenger and freight travel needed at all levels of government and in the private sector to make prudent decisions about reducing transportation GHG emissions. The results of this project would inform the data collection area described in Appendix B.


Educational Outreach for Policy Makers and Practitioners A series of workshops would likely be needed to reach decision makers with the information generated from the above projects (Burbank 2009). An

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extensive outreach effort may be necessary to reach all the individuals at various levels of government who make decisions about implementing programs. This activity would design appropriate materials and events to reach these audiences. The initial effort could be based on the results of the “low-hanging fruit” and “cost-effectiveness” projects. As additional policy guidance developed through the fundamental research program described later in this chapter is synthesized and interpreted, subsequent outreach efforts would be organized.


New Tools and Technologies The new understanding and improved tools for analysis developed by the fundamental research described below should be translated into practical revisions of handbooks, tools, techniques, and technologies that can be disseminated widely, along with appropriate training. Among the new tools might be improved guidance documents, sketch planning models, regional travel models used by MPOs to analyze policy options that are sensitive to how travelers adjust their behavior, and paving materials and techniques with reduced GHG emissions.

Structure

All these efforts would be best conducted through a research model that extensively involves stakeholders in the development of research agendas, requires merit review of competitively solicited proposals by peers, allows experts and practitioners to be represented on panels to oversee research efforts, and involves stakeholders in the peer review of the completed research.

Fundamental Research

Burbank (2009) recommends the creation of a university-based research program to conduct high-quality research addressing fundamental issues and questions that are important to resolve in analyzing, choosing, conducting, and evaluating mitigation efforts. The committee shares the belief that such research is greatly needed, but also believes that the organizations that conduct the research should be the most qualified proposers and should be selected through a competitive process based on merit and decided by peers regardless of their institutional affiliations.

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×

The topics into which the committee has organized these research areas capture most of the topics Burbank (2009) identifies in her commissioned paper and adds others that the committee believes to be important. Most of the topic areas have been introduced in the preceding sections of this chapter. Examples of the kinds of research that would be conducted through this program are described in the following paragraphs. Topics are grouped under various headings, but much of the research would span multiple topic areas. The topics are examples of the kinds of research that the committee expects would be conducted once the program becomes operational. The committee expects that experts would be convened early in the program to identify the most promising areas of investment.

Measurement and Estimation
  • Cost-effectiveness of individual mitigation strategies and combinations of strategies: If the nation comes to support the need to mitigate transportation GHG emissions and reduce energy consumption, the most important research task in the mitigation area will be to inform the selection of strategies that require the least resources. Developing these estimates will require considerable analysis and research and will depend on improved understanding of other topics listed below.

  • Life-cycle analysis for modal comparisons: Analysis is needed to refine estimates that cover all the dimensions of vehicle and modal energy consumption in obtaining fuel; in building, operating, and disposing of vehicles; and particularly in building, operating, and maintaining the infrastructure on which vehicles operate.

  • Full social cost accounting: Transportation in the United States is market driven to a considerable degree, particularly in the freight sector. However, the market transactions do not include the cost of emitting GHGs or the impact on the national economy and national security of being so highly dependent on imported fuels, much of which comes from unstable parts of the world. Improved understanding of the external costs and benefits of transportation is important in making decisions about tax rates, pricing strategies, and regulatory analyses. Considerable effort has gone into developing esti-

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
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mates of transportation externalities (see the volumes prepared by Delucchi et al.),12 and more fundamental research is needed to update and extend past work, address freight transportation, and narrow the differences of opinion that exist among experts about how to value nonmonetary costs and benefits.

  • Co-benefits and costs: As indicated above, the mitigation strategies favored by some to reduce travel may have ancillary benefits. “New urbanist” designs of residential development, for example, are thought to foster healthier lifestyles (more walking) and stronger community bonds among neighbors. Whether this is true is an empirical question that can be tested. There may also be costs that need to be better understood, such as whether families’ preferences for open space, privacy, quiet, organized children’s sports and other activities, and other amenities of suburbia are also well served in such developments.

Travel Behavior and Modeling

At the most basic level, mitigation policies are designed to modify behavior, but whether they will do so and whether the changes will be those anticipated are difficult to predict. Scholarly research in this area has not been well supported by transportation research programs in the past. Hence, the knowledge base is not as robust as needed to understand the implications of some of the mitigation proposals being suggested.

  • Individual, household, and life-cycle activities: Basic research is needed to better understand the individual, family, and life-cycle activity patterns that drive transportation demand.

  • Demographic changes: The aging of the baby boom and projected growth in immigration will affect the magnitude and nature of future travel demand, which needs to be well accounted for in forecasts of VMT and in strategies to address it.

  • Urban goods movement: The magnitude and nature of freight movements, both through and within metropolitan areas, are largely unknown due to data constraints. In addition to the data collection needs identified later in this report (Appendix B), research projects

12

See the listing of reports at http://www.its.ucdavis.edu/people/faculty/delucchi/index.php. Accessed April 22, 2009.

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×

are needed to help understand goods movement in general and how it is changing (e.g., with growth in Internet shopping).

  • Land use interactions: Of the many studies on how land use and transportation behavior interact, the small number that are well designed are unable to control for all the interacting influences that affect travel outcomes (TRB 2009). Even the best studies are cross sectional (examining relationships between variables at a single point in time), but they can only suggest associations. Longitudinal studies (which examine relationships over time) are required to establish causal relationships in hopes of understanding how to design policies that will affect outcomes, but such studies are rare in the United States. Research would initially be needed to design appropriate longitudinal studies, as recommended by Special Report 298 (TRB 2009).

    A separate set of research projects would focus on key questions for local policy makers interested in achieving VMT reductions through changes in urban form. Among such questions are the following:

    • What would be appropriate parking prices and parking maximums, and how would they vary by the density of development?

    • What changes in zoning laws, regulations, and practices are needed to encourage appropriate mixed uses of development?

    • What kinds of regional land use controls are necessary to concentrate development (see discussion of Portland and urban growth boundaries above)?

    • What elements of urban design make dense, multifamily residential areas more appealing and attractive?

    • What mix of development types (housing, retail, employment) is needed and in what proximity to residential development to create the desire for people to walk?

    • What design features of the environment are most successful in inducing walking trips?

    • How should transit be best designed to foster more compact, mixed-use development?

    • At what residential and employment density levels are different types of transit service (bus, light rail, subway) most cost-effective?

    • Little is currently understood about the magnitude of freight emissions and energy consumption within metropolitan areas and how they change with spatial structure (Bronzini 2008). Are decentral-

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
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  • ized areas more or less energy efficient from a freight distribution perspective? Do the congestion disadvantages of density outweigh the greater trip lengths of low density?

  • Demand for compact, mixed-use development appears to be underserved (Levine 2006); how could transportation energy efficiency be maximized to meet such demand?

  • New, cost-effective approaches to data collection and dissemination: Understanding travel behavior is a data-intensive area of research. The development of more cost-effective and accurate ways to collect information from representative samples of volunteers is critical in obtaining such data. Research is under way in this area, but additional work is needed to bring down costs.

  • Next-generation trip generation models: Tools for predicting travel behavior can be improved as new understanding and data are obtained. Current models are based on simplistic representations of decision making.

  • Opportunities for passenger and freight mode shift: Improved understanding of the effects of policies designed to encourage shifts in travel to modes requiring less energy and with lower emissions of GHGs (transit, water, rail) is important. Policies to be examined would include road pricing, road tolling, parking pricing, increased fuel taxes, and others designed to raise the cost of road use to incorporate externalities. In the freight area, research could examine the potential benefits and costs of raising heavy-vehicle use taxes to ensure that motor carriers pay both the cost imposed on the infrastructure and the external costs imposed on others (congestion, pollution, GHGs emitted, and so forth). Changes in regulation to encourage efficiency through increased competition and the benefits and costs of direct subsidies, such as costs for waterways infrastructure and operations not borne by users, are also worth examining.

  • Potential for trip substitution: As described earlier in this chapter, many expect that pervasive information and telecommunication technologies will substitute for trips, but so far no significant effects have been established. The research in this area is difficult, so advances in methods and data are needed to develop a better understanding of the relevant relationships.

  • Incorporating uncertainty in models used for policy analysis: The complex and global challenges of responding to climate change imply that

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they require analysis of options over a much longer time period than the 20- or 30-year horizon often used in transportation planning exercises. Adopting a long-range perspective introduces deep uncertainties about the effects of climate and technological change and how societies will respond. Methods are in development that incorporate these uncertainties into models that guide policy makers through consideration of a wide range of possible futures and adaptive strategies (Lempert et al. 2003). The choices such exercises develop for the long term can be very different from those that seem appropriate over analysis periods of only 10 or 20 years. Dewar and Wachs (2006) have suggested how these approaches to incorporating uncertainty could be applied to transportation planning in response to climate change. They criticize the transportation models currently used for regional and state long-range planning for their deterministic nature and inability to incorporate the uncertainties that characterize the challenges of responding to climate change. Fundamental research on such modeling approaches would address how they might be developed to analyze transportation policy options to respond to climate change over the long term, taking into account uncertainties about climate, technological, social, and economic changes.

Policy Analysis

Grouped together under this heading are a variety of analytical tasks needed to inform policy makers:

  • Successes and failures of past transportation interventions to meet federal air quality standards: For nearly 40 years the nation has struggled to reach national air quality standards through transportation and other measures. The mitigation strategies to reduce GHG emissions are similar to those implemented to reduce criteria emissions from vehicles. Many of these strategies are embedded in the existing federal–state policy framework, but whether they are all effective is an open question. Clearly, vehicle emissions and CAFE standards have gone a long way toward meeting Clean Air Act goals. Mandates to reduce ozone precursors have been effective in requiring local officials to become creative in addressing problems, but the so-called conformity test remains controversial. Much could be gained from

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
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scholarly evaluations of the effectiveness, costs, feasibility, and acceptability of past interventions.

  • Lessons from abroad: Most industrialized nations are already engaged in mitigating transportation emissions. Although international comparisons can be fraught with problems, much can be learned if the research is well designed. Much can also be learned about how other nations organize research to provide local policy makers with information that will help them implement the most cost-effective GHG-reducing strategies at the local level.13

  • Implementing user charges: The discussion of full social cost accounting above describes the need for research to improve the ability to quantify difficult-to-value social and environmental costs. Even if they were better known, there is a political reluctance to impose such costs. International experience with cordon tolls indicates that public support for pricing measures improves once they are implemented. The introduction of congestion pricing in Stockholm through a pilot program before the holding of a public referendum appears to have shifted support to a majority position. These examples need to be examined more closely to improve understanding of how public acceptance was achieved. More generally, research is needed to improve understanding of whether and how the public might accept marginal social cost approaches in any sector and to suggest strategies that might help move society in this direction for pricing transportation. In addition, many regulatory approaches, such as motor vehicle fuel economy standards and safety standards, have the effect of raising prices to require consumers to pay for social costs they might not fully value. Although these approaches are less efficient, they do not suffer from the same broad lack of public support as do pricing measures. The merits of these kinds of approaches should be evaluated.

  • Integrated vehicle–fuel scenarios: As indicated in the section on vehicle and fuel energy intensity, there will be an ongoing need for assessments of the potential of alternative vehicles and fuels to meet GHG emission reduction targets. As useful as such analyses are, they often have to make simplifying assumptions that may not prove realistic.

13

For example, May et al. (2008) describe how the United Kingdom developed a research initiative to help local officials make informed decisions about urban transportation and land use strategies.

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Refinements can be made through research to integrate more fully all the required dimensions of cost, rate of technology innovation, safety, performance, and so forth.

  • Equity: Many of the potentially most effective strategies aimed at modifying travel behavior involve increasing the cost of driving, which could be inequitable. There are surely ways to minimize inequitable impacts, but they are not always the obvious ones (Schweitzer and Taylor 2008). Sales taxes, for example, which are increasingly levied as an alternative to raising gasoline taxes, can place an extra burden on the poor. Research and analysis can lead to the design of policies to meet GHG emission reduction goals without placing a special burden on the least advantaged.

  • Institutions: Enacting policies that would result in significant changes in travel behavior may also require significant changes in institutions that develop such policies. Regional strategies are required in addressing travel behavior at the metropolitan scale, but MPOs are weak institutions, and most have little influence over land use policy within their regions. Furthermore, transit authorities and state, county, and city highway departments are responsive to differing legislative mandates and funding streams. Harmonizing these institutions at the regional scale is a difficult challenge that few regions have mastered. Research could inform policy makers about the consequences of reforms that have been tried in some regions.

  • Benefits of new investments in less energy-intensive modes:

    • Transit has the potential to save energy, particularly in places that support efficient and cost-effective transit. Transit currently captures about 11 percent of metropolitan area work trips and only 2 percent of trips overall, but it captures 23 percent of work trips in central cities of 5 million or more (Pisarski 2006, Table 3-23). Of course, a massive expansion of transit would be required to make a significant dent in the GHG emissions of passenger vehicles overall, given the small share of total trips that transit represents. Analysis of the particular settings in which transit strategies pay off in terms of energy savings and GHG emission reductions is needed.

    • Rail transit systems have better fuel efficiency per passenger mile than do buses. However, they are capital intensive and take decades to plan and build out to a system level, and subways require enor-

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  • mous energy to construct. The best near-term opportunities exist in places that already have rail systems, so research should focus initially on where and how system expansions make the most sense from a GHG-reduction perspective.

  • Although intercity passenger rail is about 24 percent more energy efficient than LDVs, expansion of the passenger rail network is problematic for a number of reasons. New rights-of-way for high-speed passenger rail are expensive, are difficult to obtain because of the required nearly straight and level alignments, and face significant environmental barriers. The energy costs required for the construction of the new capacity also need to be considered.14

  • Program evaluation: If the experience with the Clean Air Act is a guide, some programs implemented to influence travel will not work or will not be as effective as needed. Interventions should be rigorously evaluated by independent researchers so that ineffective programs can be discarded and potentially more effective ones implemented.

  • National-level analysis: In addition to the topics suggested above, there is a need to encourage consideration of broad, national-level strategies that encompass all of transportation—travel demand, vehicle technologies, alternative fuels, substitutes for travel—to address fundamental questions of how the transportation system, considered as a whole, could respond to the problem of climate change. The intent would be to encourage creative reconsideration of how transportation is conceived and provided in a world where carbon emissions are a binding constraint.

System Management and Operations

Many regions have implemented elements of intelligent transportation system technologies that could allow greater fine-tuning of traffic flows. To achieve the 20 percent GHG emission reduction potential cited earlier,

14

 Almost all intercity rail now operates on tracks that service both passenger and freight trains. This makes introduction of intercity passenger rail more feasible, but it reduces the speed at which passenger trains can operate and raises safety concerns. Most intercity rail lines are owned by private freight railroads, and many corridors operate near capacity for freight alone. For safety and capacity reasons, private railroads are not anxious to share tracks with passenger trains. Policy makers need information about the potential of intercity rail—particularly the cost per ton of GHGs reduced when the costs of obtaining rights-of-way, addressing safety issues, and other issues are included.

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information would probably have to be combined with speed management in ways that are becoming more common in Europe but that are not being used in the United States. Among other possibilities are more intensive management of freeway access to reduce congestion, improved incident and special event management, and real-time travel information (see Burbank 2009, Appendix A). Research on advances in these areas is needed to inform managers about the potential of different strategies, to evaluate new strategies when they are tried, and to share information with others.

Materials, Maintenance, and Construction

Research is already under way worldwide on new forms of concrete with lower GHG emissions during cement production, and asphalt pavers are already adopting European warm-mix asphalt practices that require less energy to produce and deploy. New paving materials, of course, also have to meet performance and durability standards, so evaluating these new products will remain an important line of research. The benefits from a life-cycle maintenance and GHG emission reduction perspective of switching to illumination with light-emitting diodes should be investigated. Largely underinvestigated are practices that could substantially reduce energy requirements for maintenance, such as median and right-of-way plantings that require less energy for mowing. The energy required for construction and whether there are opportunities for major savings in this area are also largely underinvestigated.

Structure

The committee concurs with Burbank’s recommendation that the fundamental research identified above should be organized along the National Science Foundation model. Under this approach, proposals would be solicited through Broad Agency Announcements (BAAs) within each topic area, the proposals would be evaluated by expert peers, only the best proposals would be funded, and the research results would be peer reviewed before publication. The illustrative topics described above are meant to identify promising areas of inquiry to inform future policy decisions. It is expected that the BAAs would identify such areas as in need of research and that the research undertaken would be based on the quality of the proposals submitted, as judged by peers in a merit review process.

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CONCLUSIONS

The effects of expected population and economic growth on transportation demand and the importance of transportation in meeting social needs will make mitigation of GHG emissions and the saving of energy in the transportation sector extraordinarily challenging. Expected improvements in technologies and fuels could make reducing transportation energy consumption and GHG emissions by 2050 to the levels of 1990 or 2000 possible, although such a goal will be difficult to achieve. Reducing them another 60 to 80 percent, if required, may not be feasible with technology and fuels alone, hence the frequent calls for reducing future travel demand or shifting it to more fuel-efficient modes. Significant carbon taxes or a carbon cap-and-trade program resulting in elevated fuel prices will stimulate demand for new vehicles and fuels. These fuel prices can be set by policy without necessarily investing more tax dollars in research on travel behavior. However, if policy makers determine that significant reductions in future travel demand are necessary, the selection of the most effective and beneficial strategies will be critical, because reductions in travel by themselves can be harmful to economic and social welfare. Unfortunately, the knowledge base for advising policy makers in this area is weak. Basic research in the area of travel behavior has not been supported, and data for policy analysis have many gaps and flaws.

Investments in surface transportation mitigation research in two main areas are recommended in this chapter. The first would provide initial guidance to policy makers and practitioners and help shape the direction of the other recommended research areas. It would also develop information and guidance for policy makers and administrators about strategies that can be implemented on the basis of available information. Transportation policy decisions are made by the federal government, all 50 states, and tens of thousands of cities and counties, and land use decisions are typically guided at the metropolitan scale but enacted at the city and county scales. Thus, the audience for this research is broad and has diverse responsibilities. Under this program, guidance would be continually updated as new data are collected and research results are provided from the recommended fundamental research program, and outreach activities to state and local decision makers would be conducted. The second would guide the conduct of the fundamental research recommended

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earlier in the chapter, which would provide new information and insight for policy analysis and guidance.

As important as identifying topics for research is managing the research in a way that is most effective in asking the right questions and employing rigorous quality control measures. Asking the right questions requires that programs be shaped by stakeholders. Employing the most rigorous quality-control measures requires allocating funds to the best among competitively solicited proposals, with awards being based on merit and decisions being made by peers. Criteria for organizing and administering a research program that meets these standards are described in Chapter 5.

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Abbreviations

BTS Bureau of Transportation Statistics

CBO Congressional Budget Office

NRC National Research Council

TRB Transportation Research Board

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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×
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Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×
Page 64
Page 65
Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×
Page 65
Page 66
Suggested Citation:"3 Mitigation Research to Inform Policy and Practice." Transportation Research Board. 2009. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299. Washington, DC: The National Academies Press. doi: 10.17226/12801.
×
Page 66
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A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy: Special Report 299 Get This Book
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In reviewing proposals for transportation research programs as part of reauthorizing the federal surface transportation program, the Transportation Research Board recognized a gap: no proposals explicitly addressed research to mitigate GHG emissions and energy consumption attributable to passenger and freight travel or to adapt to climate change. A Transportation Research Program for Mitigating and Adapting to Climate Change and Conserving Energy is the product of a study to suggest research programs to fill this and other perceived gaps.

Specifically, this book identifies research needs with regard to policies and strategies relating to the use of the transportation system and to assist infrastructure owners in adapting to climate change; focuses on research programs that could provide guidance to officials at all levels responsible for policies that affect the use of surface transportation infrastructure and its operation, maintenance, and construction; and aims to help officials begin to adapt the infrastructure to climate changes that are already occurring or that are expected to occur in the next several decades.

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