This chapter reviews the patterns and trends in transportation use of energy and impacts on the environment. These aspects of the transportation system are also important measures of performance to be taken into account along with such primary measures as system reliability, efficiency, and safety.

Recent trends show reduced U.S. petroleum dependence as a result of nearly constant domestic consumption and increased domestic production. U.S. dependence on imported oil peaked at 60.3 percent in 2006, but has since decreased from 51.5 percent in 2009 to 39.9 percent in 2012 [USDOE EIA 2013f].

In 2012 the U.S. transportation sector used 27 quadrillion Btu (British thermal unit) of energy, second only to electricity generation but down from the peak of 29 quadrillion Btu in 2007 (figure 8-1 and 8-2).¹ Transportation relied on petroleum for 92.7 percent of the energy it used in 2012, down from a peak of 97.3 percent in 1978 (figure 8-2). The United States consumes nearly 18.5 million barrels of oil per day (nearly twice as much as China's 10.3 million barrels), of which 13.0 million barrels (70.1 percent) are consumed by the U.S. transportation system. Despite transportation's dependence on petroleum, recent trends show decreasing dependence on imported petroleum, sharply reduced emissions of air pollutants, and small reductions in greenhouse gas emissions.

Aggregate national emissions of the six common air pollutants (carbon monoxide, lead, nitrogen dioxide, volatile organic compounds, particulate matter, and sulfur dioxide) dropped an average of 61.9 percent between 1990 and 2012 [USEPA 2014]. Greenhouse gas (GHG) emissions (carbon dioxide, hydrofluorocarbons, methane, and nitrous oxide) closely parallel transportation energy use and, as a result, were 17.9 percent higher in 2012 than in 1990. Since 2005, however, transportation GHG emissions have been decreasing as a result of less vehicle travel, improved energy efficiency, and increased use of biofuels. Tighter fuel economy and emission standards are expected to further reduce air pollutant emissions.

Energy Use Patterns and Trends

After four decades of oil price shocks and a variety of incentives for alternative fuels, the U.S. transportation sector remains heavily dependent on petroleum (figure 8-2). Transportation's petroleum dependence decreased from 96.7 percent in 2004 to 92.7 percent in 2012, chiefly due to increased blending of domestically produced ethanol from biomass in gasoline [USDOE EIA 2013a]. Today almost all gasoline sold in the United States contains 10 percent ethanol (E10). Nearly all transportation-related natural gas consumption, shown in figure 8-2, is used to fuel pipeline compressors. Natural gas use by motor vehicles remains a small fraction of total transportation energy use. Recently lower prices and abundant domestic supplies have increased interest in natural gas as a motor fuel.

Transportation's petroleum use is expected to remain at about 13.5 million barrels per day through 2020 and beyond, chiefly due to decreases in personal vehicle gasoline use as a consequence of tightened fuel economy standards [USDOE EIA 2013d]. However, declining personal vehicle petroleum use is projected to be offset by growth in petroleum demand by other modes, particularly medium and heavy-duty trucks. According to the Freight Analysis Framework, freight tonnage is forecast to grow annually by 1.3 percent during this period (table 4-1).

Alternative fuels use (excluding gasohol) by motor vehicles is increasing. Total alternative fuel use exceeded 500 million gasolineequivalent gallons in 2011, up 12.7 percent over 2010 levels [USDOE EIA 2013b]. In comparison, about 138 billion gallons of gasoline were consumed² in the United States [USDOE EIA 2014]. Compressed and liquefied natural gas accounted for almost onehalf of the total, followed by E85, propane, electricity, and hydrogen. E85 is a blend of between 51 percent and 85 percent denatured ethanol and gasoline and can be used safely by approximately 10 million flex-fuel vehicles operating on U.S. roads.

The highway mode dominates transportation energy use. Highway vehicles were responsible for 83.5 percent of total transportation energy use in 2011 (figure 8-3). Light-duty vehicles (passenger cars, sport utility vehicles, minivans, and pick-up trucks) accounted for three-fourths of highway energy use and 61.5 percent of total transportation energy use.

The predominance of the highway mode in transportation energy use is shown in greater detail in table 8-1. In 2011 highway vehicles used five times more energy than all other modes combined, accounting for 83.5 percent of the total. Air transport comes in a distant second with 6.7 percent of transport energy use, but this number excludes energy for international flights. Jet fuels supplied to international flights originating in the United States amounted to 939.6 trillion Btu in 2011 [USEPA 2013b]. Water transportation is third with 4.4 percent, but once again most of the energy used in international shipments is not included in this figure. An estimated 620.2 trillion Btu were supplied to international ships at U.S. ports in 2011 [USEPA 2013b]. Rail freight accounts for 2.0 percent of transportation energy use, although it carries roughly one-half of U.S. ton-miles. Transit operations are responsible for 0.6 percent of transportation energy use.

Greenhouse Gas Emissions

The transportation sector is the second largest producer of greenhouse gas (GHG) emissions, accounting for 27.3 percent of total U.S. emissions in 2011 [USEPA 2013b]. Carbon dioxide (CO₂) produced by the combustion of fossil fuels in internal combustion engines is the predominant GHG emitted by the transportation sector. In 2011 motor vehicles accounted for 95.9 percent of the 1,834 million metric tons of CO₂ equivalent emissions by the transportation sector. The four principle GHGs—methane (CH₄), CO₂, nitrous oxides (N₂O), and hydrofluorocarbons (HFC)— emitted by transportation have different global warming potentials. Figure 8-4 shows the common metric of equivalent grams of CO₂ for each emission.

Hydrofluorocarbons and other replacements for ozone-destroying gases once used in automotive air conditioners are second in importance.³ HFCs are the most potent GHGs known. GHG emission regulations for personal vehicles give manufacturers credits for reducing these emissions, and it is likely that HFC emissions will decrease in the future. Nitrous oxides are chiefly produced in the catalytic converters of motor vehicles, and a very small quantity of methane emissions is produced by incomplete combustion of fossil fuels or by leakage.

Because 95.9 percent of transportation GHG emissions are CO₂ produced by fossil fuel combustion and because petroleum comprises 92.7 percent of transportation energy use, modal GHG emissions closely track modal energy use. Transportation GHG emissions increased from 1990 to 2007, fell sharply with the economic recession in 2008, and remained at about 1,850 teragrams (million metric tons) through 2011 (figure 8-5). Evident in figure 8-5 are the results of the U.S. Environmental Protection Agency's (EPA's) decision to change the definitions of passenger cars and light trucks in 2007. Many vehicles formerly classified as light trucks, but designed predominantly for passenger transportation, were reclassified as passenger cars, causing an apparent jump in passenger car emissions that were offset by a compensating drop in light truck emissions.

Energy Efficiency

In the past, transportation reduced the growth of its energy use by improving the efficiency with which energy was used. The fuel economies of passenger cars and light trucks have closely tracked the Corporate Average Fuel Economy (CAFE) standards since they took effect in 1978 (figure 8-6). The miles per gallon (mpg) values shown in figure 8-6 are the unadjusted test values on which compliance with the standards is based. However, the actual mpg values seen on window stickers and in public advertising are adjusted downward to better represent the fuel economy drivers will likely experience on the road.

The estimated on-road fuel economy for all personal vehicles (passenger cars and light trucks) increased through 1987 but remained nearly constant through 2000. After 2000, fuel prices increased and CAFE standards were raised, first for light trucks and then for passenger cars. The apparent decrease in onroad fuel economy estimates after 2005 more likely reflects a change in the definitions of passenger cars and light trucks and the methods used to estimate their travel and fuel use than an actual decrease in miles per gallon.

Starting in 2006, the U.S. Department of Transportation (USDOT), Federal Highway Administration (FHWA) began reporting vehicle travel and fuel consumption statistics for short- and long-wheelbase light-duty vehicles rather than for the previous categories of passenger cars and two-axle, four-tire trucks.⁴ As a result, the post 2006 on-road fuel economy data are not consistent with the data from 2006 and earlier years.

Before 1975 personal vehicle travel and fuel use typically moved in parallel tracks (figure 8-7). Fuel economy improvements after 1975 broke the close connection as the amount of fuel used per vehicle mile of travel steadily decreased. The gap widened as newer, higher miles per gallon (mpg) vehicles came to dominate the on-road fleet, eventually raising average mpg from 13.3 in 1975 to 21.4 in 2012. However, drops in fuel use are tempered somewhat by increases in travel stimulated by improvements in fuel economy, a phenomenon known as the "rebound effect." ⁵ In 2012 light-duty vehicles used 76 billion fewer gallons of motor fuel than they would have assuming the same level of vehicle travel, but 1975 average on-road fuel economy. The average price of gasoline in the United States in 2012 was $3.70 per gallon, or $3.30 net of motor fuel taxes, implying a net savings due to fuel economy improvements of approximately $225 billion dollars in 2012 alone.

On August 28, 2012, the USDOT and the EPA set fuel economy and GHG emissions standards for passenger cars and light trucks through 2025. Nominally, the standards require a total fleet average of 54.5 mph (163 grams of CO2 equivalent) for new personal vehicles by 2025 [USEPA 2012]. However, this is based on laboratory test cycles rather than real world driving and does not consider the many ways manufacturers can earn fuel economy credits. Credits may be earned for more efficient air conditioners that leak less HFC, which is a potent greenhouse gas; for solar panels on hybrids; engine shut off at idle; and other features that improve real world fuel economy, but are not reflected in the test cycle. Additional credits may be earned for production of plug-in electric vehicles, hydrogen fuel cell vehicles, and vehicles powered by compressed natural gas. Furthermore, the new standards vary with the size of the vehicles a manufacturer produces. If a manufacturer produces mostly large vehicles, then its actual fuel economy requirement will be lower than if it produces mostly small vehicles.⁶Taking all these factors into account, USDOT and EPA estimated that manufacturers would achieve fuel economy levels of 46.2 to 47.4 mpg on the laboratory test cycles [FEDERAL REGISTER 2012]. Fuel economies achieved in actual driving would likely be 15 to 20 percent lower.

Medium- and heavy-duty highway vehicles are the second largest energy users among modes, accounting for 21.9 percent of transportation energy use in 2012. In 2011 the USDOT and the USEPA announced the first fuel economy and emission standards for this vehicle class for model years 2014 –2018 [USEPA 2011]. The standards apply to highway vehicles with gross vehicle weights above 8,500 pounds and set targets that vary depending on the type of vehicle and its functions. With the promulgation of these standards, nearly all highway vehicles became subject to fuel economy and CO2 emissions rules. By 2018 the requirements for combination tractor trailers specify fuel economy improvements ranging from 9 to 23 percent, depending on the truck type. Goals for pickups and vans average 12 percent for gasoline engines and 17 percent for diesels. Similar improvements are required for the diverse class of vocational vehicles, such as dump trucks, cement mixers, and school buses. The EPA standards also require reductions in methane and nitrous oxides emissions and HFC leakage.

The energy intensities⁷ of passenger modes have generally declined over time with five out of six passenger modes now averaging about 4,000 Btu per person-mile or about 30 person-miles per gallon of gasoline equivalent (figure 8-8). These declines are largely the result of more aerodynamic vehicles and efficient engines as well as improved operating efficiencies (e.g., higher air carrier load factors). In the decade from 2001 to 2011, the energy intensity of light trucks rose while that of passenger cars increased a smaller amount. The energy intensity of the other passenger modes—air, transit bus, and Amtrak —all declined.

The energy intensity of rail freight transport decreased at an average annual rate of 2.3 percent per year from 1960 –1990 and 1.6 percent per year thereafter. In 2011 moving 1 ton of freight 1 mile required 35 percent as much energy as it did in 1960. This was accomplished by reducing energy use per freight car-mile by 18.2 percent while simultaneously increasing tons carried per car-mile by 132.2 percent [USDOT BTS NTS 2013].

Alternative Fuels and Vehicles

A large part of the growing use of biofuels in transportation, shown in figure 8-2, can be attributed to the requirements of the Federal Renewable Fuels Standard (RFS). Enacted as part of the Energy Policy Act of 2005 (Pub. L. 109-58) and extended by the Energy Independence and Security Act of 2007 (Pub. L. 110-140), the RFS requires the introduction of increasing amounts of renewable energy into gasoline and diesel fuels each year, ultimately reaching 36 billion gallons by 2022 [USLOC CRS 2013]. At least 16 billion gallons must be cellulosic ethanol,⁸and no more than 15 billion gallons can be ethanol produced from corn starch. In 2011 the United States produced and consumed 14 billion gallons of fuel ethanol and 878 million gallons of biodiesel [USDOE EIA 2013c]. In comparison, a total of 36 billion of gallons of diesel fuel were consumed by vehicles in 2012 [USDOE EIA 2013h].

The RFS is currently facing two important challenges: 1) there is still almost no capacity to produce cellulosic ethanol, which has led the EPA to reduce cellulosic ethanol requirements every year and, 2) the blending of ethanol with gasoline is very close to market saturation at the current 10 percent level. This means that additional ethanol production can only be absorbed by expanding the current distribution network of high ethanol blend fueling stations and increasing the numbers of vehicles capable of using these higher blends—up to and including E85 (85 percent ethanol, 15 percent gasoline). In 2013 the EPA decreased the requirement for cellulosic ethanol from 14 billion to 6 million gallons per year, less than one one-thousandth of the statutory amount, reflecting the absence of adequate production capacity for cellulosic ethanol. The EPA also has expanded the types of biofuels that can qualify under the RFS program to include such fuels as gasoline produced from biomass. At present, however, the capacity does not exist to produce these fuels in volumes that could make a meaningful contribution to achieving the RFS goals.

Nearly all U.S. gasoline now contains up to 10 percent ethanol. All automobile manufacturers' warranties allow 10 percent ethanol/90 percent gasoline blends (E10). In 2012 motor vehicles used 134 billion gallons of gasoline, including almost 13 billion gallons of ethanol [USDOE EIA 2013c]. Higher levels of ethanol of up to 15 percent (E15) may pose difficulties for motorcycles, older vehicles, and off-highway engines. The EPA has not approved nor tested E15 for proper engine performance and fuel economy in motorcycles [FRANK 2013]. Generally, manufacturers have been reluctant to extend their warrantees to include higher level blends. The 10-percent limit has been termed the "blend wall," in that it appears to constrain the amount of ethanol that can be safely mixed with gasoline as a strategy for meeting the RFS. In 2011, after extensive study, the EPA issued a rule permitting E15 use in model year 2001 and newer motor vehicles (the majority of personal vehicles on the road). However, manufacturers have challenged the ruling based on concerns about the potential for misfueling of older vehicles not capable of using E15 without risking mechanical problems. Concern about the potential risk of misfueling appears to be responsible for the very limited availability of E15. As of June 2013 there were only 24 refueling stations in the United States, out of a total of approximately 150,000, offering E15 [ODELL 2013].

Flexible-fuel vehicles (FFVs) can safely use mixtures of up to 85 percent ethanol (E85) with gasoline.⁹ In 2011 there were approximately 10 million FFVs operating on U.S. roads, but only about 10 percent have used E85 [USDOE EIA 2013e]. Until 2016 automobile manufactures can earn extra credits toward meeting Corporate Average Fuel Economy (CAFE) standards by making and selling FFVs. Future FFV sales are uncertain because the credits will be largely phased out by 2016 unless actual use of E85 increases substantially.

Electrically driven motor vehicles may someday transform transportation energy use, but at present there is substantial uncertainty about their ability to compete with the internal combustion engine. Until recently, gasoline or diesel fuel alone powered nearly all motor vehicles. The first mass-produced hybrid electric vehicle (HEV), powered by an internal combustion engine and an electric motor, was introduced in 1999. The internal combustion engine still provides all the energy for a hybrid vehicle, but kinetic energy normally wasted during braking is instead used to generate electricity that is stored in an onboard battery for later use by the electric motor. Hybrid vehicle sales have grown from 17 vehicles sold in 1999 to 432,000 vehicles in 2012 (figure 8-9) [USDOT BTS NTS 2013]. In 2013, 39 makes and models of hybrid vehicles were offered for sale in the United States [USDOE and USEPA 2013], and sales through the first three quarters of the year totaled 390,000 out of 11.6 million conventional vehicles [USDOC BEA 2013].

The first mass-produced "plug-in" hybrid electric vehicles (PHEV), able to draw electric power from the utility grid and store it on-board, were 2011 model year vehicles sold in 2010. In 2010 just 19 electric-only and 325 plug-in hybrid vehicles were sold. Through September 2013, combined sales of grid-connected vehicles exceeded 67,000 units. Over the same period the number of makes and models of battery electric-only vehicles increased from 3 to 10, while plug-in hybrid offerings increased from 1 to 4. Despite this growth, hybrid and grid-connected vehicles comprised just 3.6 percent of total 2012 light-duty vehicle sales of 13.3 million and a small percentage of vehicles on the road. Both types of vehicles face several challenges: reducing costs, overcoming the market's unfamiliarity with the new technology, decreasing the length of time required for recharging batteries, and developing a recharging infrastructure. Considerable progress has been made in creating a nationwide recharging infrastructure. By fall 2013, 6,686 nonresidential recharging stations had been installed across the United States [USDOE EIA AFDC 2013].¹⁰

The geographical distribution of refueling stations for alternative fuels partly reflects the numbers of vehicles in each state but also reflects the interests of residents and public policies. E85 stations are disproportionately concentrated in states that grow corn and produce ethanol (figure 8-10). The distribution of electric vehicle recharging stations tends to favor states that have opted into California's Zero Emission Vehicles (ZEV) standards (figure 8-11).¹¹ Manufacturers selling electric vehicles in these states earn credits towards meeting the ZEV requirements. The distribution of compressed and liquefied natural gas refueling stations, on the other hand, more closely reflects the number of CNG/LNG vehicles registered in the state (figure 8-12). Natural gas vehicles save their operators money on energy costs; help fleets meet national clean, alternative fuel vehicle requirements; and help reduce harmful emissions in urban areas.

Transportation's Energy Outlook

The U.S. Department of Energy (USDOE), Energy Information Administration (EIA) has projected the likely effects of current trends and existing policies on transportation's future energy use and GHG emissions. The 2013 projections anticipate transportation energy use remaining at or near the current level of 27 quadrillion Btu for the next three decades [USDOE EIA 2013d]. Existing fuel economy and GHG emissions standards are expected to decrease light-duty vehicle energy use by 20 percent by 2030 and 28 percent by 2040, resulting in a little more than 12 quadrillion Btu of energy use (figure 8-13). Most of this reduction is expected to be offset by growth in energy use by medium and heavy-duty trucks, although that could change if fuel economy and emissions standards for those vehicles are further tightened. For all other modes, activity growth is approximately balanced by improvements in energy efficiency. These projections are based on existing policies and increasing oil prices. Natural gas use by motor vehicles in compressed and liquefied form is projected to increase from just 0.04 quads in 2010 to 1.1 quads by 2040. EIA attributed all of the projected increase in natural gas use by motor vehicles to medium- and heavy-duty trucks and buses.

According to the EIA, the 2011-2025 fuel economy standards, together with the market's response to higher gasoline prices, are projected to save personal vehicle owners about 40 billion gallons of motor fuel in 2025 compared to what consumption would have been at the same level of vehicle travel without any increase in fuel economy (figure 8-14).

By fuel type, gasoline use declines from 16.8 quads in 2010 to 12.6 in 2040, in line with light-duty vehicle energy use. Diesel fuel use increases from 5.8 to 7.9 quads, which is consistent with the growth of truck freight energy use. E85 and electricity use increases but will still amount to only 0.17 quads and 0.07 quads of energy in 2040, respectively.

Air and Water Quality, Noise, and Habitat Impacts

Vehicle emissions controls and other policies have reduced all of transportation's air pollutant emissions in comparison to their 1990 levels, a trend that continues in the most recent years. From 2009 to 2013, emissions from every one of the air pollutants declined from year to year (figure 8-15). Motor vehicles are the primary source of GHG (as shown in figure 8-5) and their emissions have been linked to negative effects on our respiratory and cardiovascular health [CDC 2010]. Smog-forming emissions of volatile organic compounds (VOC) and nitrogen oxides (NO_x) were 65.6 to 42.2 percent lower, respectively, in 2013 than they were in 1990. In recent years, NO_x emissions have decreased more rapidly, partly due to more advanced diesel emission controls and the use of cleaner, ultralow sulfur diesel fuel.

Transportation's share of total U.S. PM-2.5 emissions decreased from 8.2 percent in 1990 to 5.9 percent in 2013, while the share of PM- 10 emissions decreased from 2.6 in 1990 to 2.2 percent of total emissions over the same period.

Emissions of ammonia (NH₃) increased between 1990 and 2001, and in 2013 were 38.1 percent of the 1990 level. Transportation comprised 2.4 percent of total U.S. emissions of ammonia in 2013.¹² Emissions of sulfur dioxide (SO₂) are 87.8 percent lower in 2013 than 1990, due in large part to reductions in the sulfur contents of gasoline and diesel fuel.

Reductions in transportation's pollutant emissions have contributed to improved air quality in the Nation's urban areas. In 87 continuously monitored urban areas, the number of days of nonattainment of at least one National Ambient Air Quality Standard decreased from 4,091 in 1990 to 1,012 in 2010 (figure 8-16). Although the total number of nonattainment days had been reduced by 75.3 percent, most cities still experienced at least one day in the year with poor air quality. Of the 87 cities continuously monitored, 83 had at least 1 nonattainment day in 1990 and 80 had at least 1 day in 2010.

Spills of crude oil and petroleum products from pipelines, ships, railroad cars, and tank trucks pollute surface waters and navigable waterways.¹³ The annual volume spilled varies greatly from year to year and is strongly affected by infrequent, large events (figure 8-17). For example, Hurricane Katrina caused numerous spills into navigable waterways from a variety of sources in Louisiana and Mississippi in 2005 as the volume of petroleum spilled jumped from 1.4 million gallons in 2004 to 9.9 million in 2005.¹⁴

While the number fluctuates from year-toyear, the number of spills from vessels in 2011 was the lowest in more than two decades. The number of spills from pipelines in 2011 was also substantially below the annual average. In 1985, in response to a congressional requirement, the USEPA began an effort to regulate underground storage tanks that can contaminate ground water, to clean up leaks, and prevent them in the future [USEPA 2013c]. Since then, the number of new leaks from storage tanks has been reduced by nearly an order of magnitude, and over 80 percent of all leaks have been cleaned up (figure 8-18).

As rainwater or snowmelt runs off transportation infrastructure, like roads, parking lots and bridges, it picks up de-icing salts, rubber and metal particles from tire wear, antifreeze and lubricants, and other wastes that may have been deposited on infrastructure surfaces. The runoff carries these contaminants into streams, lakes, estuaries, and oceans [USEPA 2010].

Highways and other transportation infrastructure also affect wildlife via road kills, habitat loss, and habitat fragmentation. Numerous projects have been undertaken across the United States to mitigate these impacts, from salamander and badger tunnels to mountain goat underpasses on highways to fish passages through culverts.¹⁵ There are no systematic estimates of the numbers of wildlife killed by transportation vehicles in the United States. In certain circumstances, the population effects of road kill have been shown to be substantial, even threatening the survival of endangered species. In general, the number of bird kills greatly exceeds the number of mammals killed. Annual deer kills from road accidents alone have been estimated at between 720,000 and 1.5 million [FORMAN 2003].

Transportation noise is pervasive and difficult to avoid in the United States [USDOT FHWA HEP 2013]. It is generated by engines, exhaust, drive trains, tires, and aerodynamic drag. At freeway speeds tire-pavement noise dominates for highway vehicles, while exhaust and aerodynamic noise dominate for aircraft. However, a national noise exposure inventory does not exist. The United Kingdom has developed a noise inventory for 23 large urban areas by estimating noise levels using computer models that are based on transportation activity data [UKDEFRA 2014]. Similar methods could be applied to collect and analyze noise issues in the United States.

Unwanted noise can have a variety of impacts including annoyance, sleep disruption, interference with communication, adverse impacts on health and academic performance, and consequent reductions in property values. There is almost no part of the United States in which transportation noise is not noticeable [WAITZ 2007]. When transportation noise levels are below 45 decibels (dB) the level of annoyance in the population is negligible, but when noise levels exceed 65 dB, impacts can be severe.¹⁶ Although highways are the most widespread source of transportation noise, exposure to transportation noise is systematically measured only for aircraft. In 1970, 7 million people resided in high noise (> 65 dB) areas around U.S. airports. By 1990 that number had been reduced to 2.7 million through a combination of changes in engine and airframe design and operational strategies. In 2011 just over 300,000 individuals lived in areas with excessive aircraft noise [USDOT BTS NTS 2013]. Take-off and landing operations are the primary source of annoying aircraft noise, which per dB is generally more annoying to the public than highway or rail noise.

The extent and severity of highway noise can be only indirectly inferred from statistics on the construction of noise barriers, which can typically reduce noise exposure by 10 dB, or one half. Barriers, which typically cost $1–2 million per mile to construct, provide a partial measure of the economic impacts of highway noise.

Under certain circumstances, unwanted and unnecessary light is considered "light pollution" [MRSCW 2014]. Transportation vehicles and facilities can be sources of light pollution. While light pollution is a special concern for facilities like astronomical observatories, it is also known to adversely affect biodiversity in urban areas and to have harmful effects on human metabolism [COE 2010]. No systematic data on light pollution due to transportation in the United States exists.

In addition to the primary performance measures of how efficiently, reliably, and safely people and goods move on the system, transportation's energy usage and its environmental impacts are also important measures of how well the transportation system performs its societal function. In recognition of this, there have been efforts to mitigate transportation's dependence on petroleum and environmental impacts. As detailed in this chapter, transportation has become more efficient over the past few decades in its use of energy and has reduced many of its environmental impacts even though activity levels have increased. It continues, however, to be the second leading emitter of greenhouse gases in the United States and has had other major impacts on the environment, such as oil pollution, habitat loss, and noise. Going forward, appropriate and accurate data will be needed to monitor progress and determine whether societal efforts to improve the system's performance are having the desired effect.

References

Centers for Disease Control and Prevention (CDC). Recommendations for Improving Health through Transportation Policy (April 2010). Available at http://www.cdc.gov/transportation/ as of February 2014.

Council of Europe (COE). 2010. Resolution 1776: Noise and Light Pollution. Available at http://assembly.coe.int/ as of January 2014.

Federal Register, 2017 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions and Corporate Average Fuel Economy Standards, vol. 77, no. 199, Part II, pp. 62623- 63200. Available at http://www.gpo.gov/ as of October 2013.

Forman, R.T.T. et al. 2003. Road Ecology: Science and Solutions (Island Press: Washington, DC).

Frank, A. 2013. "Ethanol-Blended Fuels: Pay at the Pump?" Motorcyclist. August 1. Available at http://www.motorcyclistonline.com/ as of October 2013.

Greene, D.L. 2012. "Rebound 2007: Analysis of National Light-Duty Vehicle Travel Statistics," Energy Policy, vol. 41, pp. 14-28.

Municipal Research and Services Center of Washington (MRSCW). 2014. "Light Nuisances – Ambient Light, Light Pollution, Glare." Available at http://www.mrsc.org/ as of January 2014.

Odell, J. 2013. "Controversial E15 Fuel Blend Is on the Way," Edmunds.com, 9/11/2013. Available at http://www.edmunds.com/ as of October 2013.

United Kingdom Department of Environment, Food and Rural Affairs (UK DEFRA), 2014. Noise Mapping England. Available at http://services.defra.gov.uk/ as of January 2014.

U.S. Department of Commerce (USDOC), Bureau of Economic Analysis (BEA). 2013. Motor Vehicles. Available at http://www.bea.gov/ as of January 2014.

U.S. Department of Energy (USDOE), Alternative Fuels Data Center (AFDC). 2013. Electric Vehicle Charging Station Locations. Available at http://www.afdc.energy.gov/fuels/electricity_locations.html as of October 2013.

U.S. Department of Energy (USDOE), Energy Information Administration (EIA):

—2014. U.S. Product Supplied of Finished Motor Gasoline (July 2014). Available at http:// www.eia.gov/ as of August 2014.

—2013a. "Transportation Sector Energy Consumption Estimates," Annual Energy Review, table 2.1e, "Transportation Energy Consumption", Monthly Energy Review, table 2.5. Available at www.eia.gov as of October 2013.

—2013b. Alternative Fuel Vehicle Data. Available at http://www.eia.gov/renewable/afv/ as of October 2013.

—2013c. "Biofuels markets face blending constraints and other challenges." Today in Energy. Available at http://www.eia.gov/ as of October 2013.

—2013d. 2013 Annual Energy Outlook, Available at http://www.eia.gov/ as of October 2013.

—2013e. "Alternative Fuel Vehicles in Use 2011." Available at http://www.eia.gov as of October 2013.

—2013f. Monthly Energy Review, tables 2.5 and 3.1. Available at http://www.eia.gov/ as of October 2013.

—2013g. Federal and State Laws and Incentives. Available at http://www.afdc.energy.gov/laws/ as of January 2014.

—2013h. Distillate Fuel Oil and Kerosene Sales by End Use (November 2013). Available at http://www.eia.gov/ as of August 2014.

U.S. Department of Energy (USDOE) and Environmental Protection Agency (USEPA), 2013. Hybrid Makes and Models and Electric- Only Vehicle. Available at www.fueleconomy.gov as of October 2013.

U.S. Department of Transportation (USDOT), Bureau of Transportation Statistics (BTS). National Transportation Statistics. Available at http://www.bts.gov/ as of October 2013.

U.S. Department of Transportation (USDOT), Federal Highway Administration (FHWA), Office of Planning, Environment and Realty (HEP). 2013. Highway Traffic Noise in the United States: Problem and Response. Available at http://fhwa.dot.gov/ as of October 2013.

U.S. Environmental Protection Agency (USEPA):

—2014. Air Quality Trends (April 2014). Available at http://www.epa.gov/ as of July 2014.

—2013a. National Emissions Inventory Air Pollutant Emissions Trends Data, 1970- 2012 Average Annual Emissions All Criteria Pollutants. Available at http://www.epa.gov/ as of October 2013.

—2013b. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2011, EPA 430-R- 13-001 (Washington, DC: April).

—2013c. Underground Storage Tanks. Available at http://www.epa.gov/oust/ as of October 2013. —2012. EPA and NHTSA Set Standards to Reduce Greenhouse Gases and Improve Fuel Economy for Model Years 2017-2025 Cars and Light Trucks, EPA- 420-F-12-051, August. Available at http://www.epa.gov/ as of October 2013.

—2011. EPA and NHTSA Adopt First-Ever Program to Reduce Greenhouse Gas Emissions and Improve Fuel Efficiency of Medium- and Heavy- Duty Vehicles, EPA-420-F-11-031, August. Available at http://www.epa.gov as of December 2013.

—2010. Controlling Nonpoint Source Runoff Pollution from Roads, Highways and Bridges, EPA-841-F-95-008a. Available at http://www.epa.gov/ as of October 2013.

U.S. Library of Congress (USLOC), Congressional Research Service (CRS)

—2013a. Deepwater Horizon Oil Spill: Recent Activities and Ongoing Developments, Congressional Research Service, 7-5700, R42942, January 31, 2013, Washington, DC.

—2013b. Renewable Fuels Standard (RFS): Overview and Issues, Congressional Research Service, Washington, D.C., March.

Waitz, I.A., R.J. Bernhard and C.E. Hanson, 2007. "Challenges and Promises in Mitigating Transportation Noise," The Bridge, vol. 37, no. 3, pp. 25-32.

¹Total transportation energy use reported here is almost 2 quads higher than the detailed modal breakdown shown in table 8-1. This is due to differences in definitions, data sources, and estimation methods. For example, table 8-1 excludes some off-highway used of gasoline and diesel fuel as well as energy for international air transport and shipping.

² EIA uses product supplied to approximately represent consumption of petroleum products. It measures the disappearance of these products from primary sources, such as refineries, natural gas processing plants, blending plants, pipelines, and bulk terminals.

³ The original coolants were chlorofluorocarbons (CFCs), which when released into the atmosphere were found to create holes in the stratospheric ozone layer that helps to protect the Earth's surface from harmful radiation.

⁴ A vehicle's wheelbase is the distance from the center of its rear axle to the center of its front axle. "Shortwheelbase" light-duty vehicles include passenger cars, pick-up trucks, vans, minivans, and sport-utility vehicles with wheelbases less than or equal to 121 inches. The same types of vehicles with wheelbases longer than 121 inches are classified as "long-wheelbase" light-duty vehicles. Typically, light-duty vehicles have gross vehicles weights of less than 10,000 pounds.

⁵There is a reasonable consensus in the economics literature that the rebound effect over this period of time induced a 1 percent to 2 percent increase in vehicle travel for each 10 percent increase in fuel economy (GREENE 2011).

⁶The size of a vehicle is defined as the rectangular "footprint" formed by its four tires. A vehicle's footprint is its track (width) multiplied by its wheelbase (length).

⁷Energy intensity is the amount of energy used to produce a given level of output or activity, e.g., energy use per passenger-mile of travel.

⁸Cellulosic ethanol is produced from non-food based feedstock, such as wood and crop residues (corn husks, cobs and stalks), and switch grass.

⁹E85 may contain anywhere from 51 percent ethanol to 85 percent ethanol. Because fuel ethanol is denatured with approximately 2 percent to 3 percent gasoline, E85 is typically no more than 83 percent ethanol.

¹⁰ A single electric vehicle recharging station may include multiple recharging outlets. Residential recharging locations are not included in the station count.

¹¹ Connecticut, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont, Washington, Delaware, Georgia, and North Carolina have adopted the California Air Resources Board (CARB) regulations for a vehicle class or classes in accordance with the Section 177 of the Clean Air Act.

¹²Ammonia is not a by-product of fuel combustion but is formed in a vehicle's three-way catalytic emissions control systems. The introduction of 3-way catalytic converters initially caused increased NH3 formation but this was later offset by improvements in newer emissions control systems and the aging and retirement of vehicles with the earliest 3-way catalytic systems.

¹³ Spills of hazardous materials in general are covered in Chapter 7.

¹⁴ The much larger Deepwater Horizon release of 206 million U.S. gallons is not included in the database of spills into navigable waterways of the United States and is not considered to be a spill from a transporting vessel (USLOC CRS 2013).

¹⁵ While there are no comprehensive statistics on mitigation efforts, numerous case studies of highways mitigation efforts can be found at http://www.fhwa.dot.gov/environment/wildlife_protection/index.cfm .

¹⁶ Noise (sound) is measured in decibels (dB) on a logarithmic scale. Each increase of 10 dB represents a doubling of the noise level.