The U.S. Department of Transportation, under its human and natural environment strategic goal, is committed to protecting and enhancing communities and the natural environment affected by transportation. The economic and societal benefits provided by transportation also generate environmental impacts, and the sector's dependence on fossil fuels is at the root of many of these environmental problems. Construction of transportation infrastructure and facilities, and vehicle manufacturing, maintenance, use, and disposal affect the environment as well.
Transportation energy use has grown an average of 1.5 percent per year for the past two decades. Still, this growth rate is slower than that of the Gross Domestic Product and passenger-miles of travel, reflecting in part a general decline in the energy intensity of almost all modes. Today, however, the transportation sector consumes a greater share of petroleum (66 percent) than it did in 1973 (50 percent). The use of alternative and replacement fuels to reduce foreign oil dependence and environmental impacts has increased, but, despite incentives in place to promote these fuels, they still accounted for only a small faction of total motor vehicle fuel use in 2000.
Growth in energy consumption is causing a corresponding increase in greenhouse gas (GHG) emissions. The transportation sector emitted 1,819 million metric tons of carbon dioxide in 1999, an increase of 14.9 percent since 1990. Three-quarters of GHG emissions come from the use of highway vehicles. In addition to GHG emissions, transportation remains a primary source of emissions of three of the six air pollutants regulated under the Clean Air Act: carbon monoxide, nitrogen oxides, and volatile organic compounds. However, with the exception of nitrogen oxides, these emissions have been declining since 1990.
Transportation vehicle use can result in hazardous materials and oil spills. An average of 1.5 million gallons of oil is spilled into U.S. waters each year. In 1999, 24 percent of this oil was cargo carried by marine vessels, pipelines, railcars, and tank trucks.
Transportation infrastructure and its maintenance can also be sources of environmental damage. Each year the U.S. Army Corps of Engineers dredges an average of 271 million cubic yards of sediments from navigation channels. Contaminated sediments are confined in various ways, while the balance may be used beneficially to nourish beaches and wetlands. Sediments become contaminated from pollutants released into the nation's waters. Similarly, petroleum stored in underground tanks has a history of leaking into soils and ultimately into surface and underground waters. By 2001, after a decade of focused effort by the U.S. Environmental Protection Agency (EPA), there were almost 150,085 known petroleum tank releases around the country waiting to be cleaned up. The leaking of methyl-tertiary-butyl-ether (MTBE), largely from underground storage tanks, was recognized in 2000 as an issue serious enough for EPA to ask the U.S. Congress to ban or reduce its use as an additive in gasoline.
Rubber tires and lead-acid batteries are two of the few transportation wastes quantified on an annual basis. States and local governments often promote the establishment of systems to recycle these wastes at the end of their lifetime. However, while over 93 percent of the lead content of batteries was reused in 1999, only 24 percent of the 4.5 million tons of scrap tires generated were recycled. This left almost 3.5 million tons of car, truck, and motorcycle tires to be disposed of in landfills or incinerated.
Preservation of wetlands, urban sprawl, invasive species, and environmental justice are also areas of concern. The United States has an estimated 105 million acres of wetlands. An equal amount may have been lost since the 1600s, drained to develop rural and urban areas. Transportation affects wetlands when roads and railroads are built and people and cargo are moved through them and when airports and other facilities are placed in them.
As the economy has grown, so too has transportation energy use. From 1980 to 2000, transportation energy use grew from 19.7 quadrillion (quads) British thermal units (Btu) to 27.0 quads, an annual growth rate of 1.5 percent . The overall growth rate is lower than that of the economy (as measured by Gross Domestic Product (GDP)) and the growth rate in passenger-miles, but not population (figure 1). It is influenced by a combination of factors, including changes in transportation intensity of U.S. GDP, vehicle fuel efficiency, and personal travel propensity.
For decades, the transportation sector has accounted for between 25 percent and 27 percent of total U.S. energy consumption (table 1). In 1999, highway vehicles accounted for just over 80 percent of transportation energy use. Passenger cars used 36 percent of the sector's total, followed by light trucks (including minivans, pickups, and sport utility vehicles) with 26 percent, and heavier trucks with 19 percent. Among the nonhighway modes, air transportation is the biggest and fastest growing energy user. The pipeline mode, which accounted for about 3 percent of total transportation energy use, is the only mode that does not depend directly on petroleum. Typically, pipelines use natural gas and/or electric pumps to move products (figure 2).
1. U.S. Department of Energy, Energy Information Administration, Annual Energy Review 2000, DOE/EIA-0384(2000) (Washington, DC: August 2001).
In the United States, petroleum consumption has risen faster in the transportation sector than in any other since 1973, before the first oil embargo. Continued growth in transportation activities has contributed, in large part, to the increase in oil consumption. While the oil price shocks of 1973-74 and 1979-80 depressed demand for a while, they did little to shake transportation's dependence on oil. Only a small fraction of transportation's energy needs are met by nonpetroleum sources, such as natural gas, methanol, and ethanol. Nonpetroleum sources are used primarily as gasoline blending agents to meet requirements of the Clean Air Act Amendments of 1990.
From 1973 to 2000, the residential and commercial buildings sector cut petroleum use in half, and the utilities sector reduced oil use by more than 60 percent. Over the same period, industrial sector oil use hovered between 4 million barrels per day (mmbd) and 5 mmbd, primarily because petroleum is an important feedstock for the petrochemicals industry. In contrast, oil use in the transportation sector rose from 9.05 mmbd in 1973 to 12.99 mmbd in 2000, an increase of about 41 percent. Due to these changes in consumption patterns among sectors, transportation today accounts for 67 percent of total U.S. petroleum demand compared with about 50 percent before 1973  (figure 1).
The U.S. Department of Energy (DOE) expects the heavy concentration of oil demand in the transportation sector to continue. In fact, DOE projects overall petroleum demand to grow at an average annual rate of 1.5 percent through 2020, led by growth in the transportation sector. Given this, transportation's share of petroleum consumption would rise to 70 percent .
1. U.S. Department of Energy, Energy Information Administration, Annual Energy Outlook 2002, DOE/EIA-0383(2002) (Washington, DC: December 2001).
2. ____. Annual Energy Review 2000, DOE/EIA-0384(00) (Washington, DC: August 2001), table 5.12a.
Spurred by energy and environmental legislation, the use of alternative and replacement fuels in motor vehicles is growing, but not enough to indicate a trend away from the use of petroleum in the transportation sector. Between 1992 and 2000, estimated alternative fuel use grew by 5.9 percent annually (table 1). Nevertheless, alternative fuels comprise a tiny fraction of total motor vehicle fuel use-0.17 percent in 1992 and 0.22 percent in 2000. Alternate fuel growth is in proportion to the rise in the number of alternative fuel vehicles (table 2) .
Replacement fuels-alcohols and ethers (oxygenates)-are blended with gasoline to meet the requirements of the Clean Air Act Amendments of 1990. They comprise a larger proportion of the motor fuel market than alternative fuels, as shown in figure 1. Unlike petroleum, which is composed entirely of hydrogen and carbon atoms, alcohols and ethers contain oxygen and are derived from energy sources other than petroleum.
In areas where carbon monoxide emissions are a problem, fuel providers have been required since 1992 to add oxygenates to gasoline to promote more complete combustion. Gasoline that contains oxygenates is referred to as reformulated gasoline (RFG). Beginning in 1994, areas failing to attain air quality standards for ozone were required to use RFG, which must contain 2 percent oxygen by weight. In 2000, oxygenates made up 3.3 percent of the gasoline pool .
The most popular oxygenate is methyl-tertiary-butyl-ether (MTBE), a combination of methanol and isobutylene, made from natural gas. MTBE has several attributes that favor its use over ethanol as an oxygenate. However, the substance has been discovered-first in California in 1995-leaking from pipelines and storage tanks into drinking water. While MTBE is not classified as a carcinogen, studies have shown it can cause cancer in animals, and trace amounts of MTBE in water supplies produce an unpleasant order and taste. Various efforts are underway or being considered by 13 states, the U.S. Congress, and the U.S. Environmental Protection Agency to reduce or ban the use of MTBE as an oxygenate. As a result, the Energy Information Administration (EIA) projects that the amount of MTBE used by domestic refiners will be cut in half by 2004 to 123,000 barrels per day. Most of this decline in consumption results from a ban on MTBE in California due to begin at the end of 2002 . However, subsequent to EIA's analysis, California decided to delay its ban until the end of 2003 because of a lack of infrastructure to assure adequate supplies of ethanol reformulated gasoline.
1. U.S. Department of Energy, Energy Information Administration, Annual Energy Outlook 2002, DOE/EIA-0383(2002) (Washington DC: December 2001).
2. ____. Alternatives to Traditional Transportation Fuels 1999 (revised), available at http://www.eia.doe.gov/fuelalternate.html, as of Jan. 8, 2002.
The United States imports over 50 percent of its crude oil supplies, and changes in world prices of crude oil can have significant, direct impacts on the U.S. economy. Despite volatility in these prices, however, the transportation sector is not particularly responsive (i.e., has very low elasticity of demand). The disinclination of fuel users to replace petroleum with alternative fuels is a reason for this inelasticity.
World oil prices more than tripled between January 1999 and September 2000 as a result of oil production cutbacks by the Organization of Petroleum Exporting Countries (OPEC), with the cooperation of Mexico, Norway, and Russia (figure 1). This oil price hike prompted concern that oil dependence may once again have a serious effect on the transportation sector and the economy as a whole. However, in late 2000 world crude prices started to drop from their high of $32.86 per barrel, as a worldwide economic downturn began. By the end of 2001, prices had reached $18.69 per barrel, similar to the price in July 1999.
A Bureau of Transportation Statistics (BTS) analysis conducted in mid-2000 of the economic impact of the 1999/2000 increase in fuel prices estimated that, to drive the same distance and produce the same Gross Domestic Product as in 1999, U.S. households and businesses would have to spend an additional $67 billion (28 percent more) on transportation fuel in 2000 . BTS concluded that households would absorb half of the additional cost and for-hire transportation firms about one-third, with the rest of the cost absorbed by nontransportation firms.
The average motor fuel cost to consumers on a per vehicle-miles traveled basis closely follows the trend in world crude oil prices (figure 2). At the beginning of 1997, on average, it cost Americans 7.5 cents to buy fuel to drive 1 mile. Then, as the world crude oil price fell below $10 per barrel (the lowest point in recent years), the fuel cost for driving 1 mile dropped to 5.5 cents, also the lowest point in recent years. Overall, the tripling of the price of crude oil in 1999 and 2000 caused the average fuel cost per mile to increase about 70 percent. Reflecting the low elasticity of demand, vehicle-miles traveled tends to fluctuate seasonally, rather than in response to world oil prices (figure 3).
1. U.S. Department of Transportation, Bureau of Transportation Statistics, "The Economic Impact of the Recent Increase in Oil Prices," Transportation Indicators: A Prototype, May 2000.
The amount of energy required to carry passengers and freight has declined on a per unit basis. Between 1980 and 1999, automobile energy use per passenger-mile of travel (pmt) by car fell by 13 percent (figure 1). This has occurred even though the average fuel economy of new car and light truck fleets leveled off in the 1990s .
Commercial air carriers reduced energy use per passenger-mile by more than 33 percent over the 1980 to 1999 period, due largely to higher occupancy . Flying a full plane requires considerably less than twice the amount of fuel of a half-full one but yields twice the passenger-miles. Airlines have been increasingly successful in filling their planes; in some cases, reconfiguring seating to fit more passengers. Moreover, although newer airplanes are more efficient, this probably has less effect on energy intensity than the greater number of passengers.
The energy intensity of Amtrak intercity rail and intercity bus declined as well (-4 percent and -11 percent, respectively). At 964 British thermal units (Btu) per pmt in 1999, intercity buses are considered the most energy-efficient mode of transportation. Energy use per pmt on transit buses, however, increased 64 percent over this period to 4,610 Btu per pmt . From a high of 3,828 Btu per pmt in 1994, by 1999 rail transit energy intensity had declined 17 percent to 3,168 Btu per pmt.
Because of data limitations and availability, less is known overall about the energy intensity of freight transportation, particularly the waterborne and heavy truck modes. Some data are available, however, and, in general, energy use per vehicle-mile has decreased, albeit slowly. The decrease in highway energy use per vehicle-mile combined with a general increase in truck size and weight limits suggest that truck energy use per ton-mile has also decreased. The energy intensity (in Btu per vehicle-mile) of heavy single-unit and combination trucks grew half a percent annually from 1989 to 1999. On a Btu per ton-miles basis, the energy intensity of Class I freight rail declined 1.9 percent while that of domestic waterborne commerce grew 1.3 percent annually between 1989 and 1999 .
It is important to note that intermodal comparisons should be considered approximations. Modal data are collected in different ways and based on different assumptions. Passenger-mile data are more relevant for passenger vehicles, while vehicle-mile or ton-mile data are more relevant for freight vehicles. Modes also perform different functions and serve different travel markets.
1. Davis, Stacy C., Transportation Energy Data Book, Edition 21 (Oak Ridge TN: Oak Ridge National Laboratory, 2001), tables 2.11 and 2.12.
2. ____. Table 2.14.
Passenger cars and light trucks are more fuel-efficient today than they were in 1978, when fuel economy standards were first implemented. Technologies like fuel injection engines, lockup torque in transmissions, and improved rolling resistance of tires have played a major role in this change. Between 1978 and 1988, new passenger car average fuel economy shot up from 19.9 miles per gallon (mpg) to 28.8 mpg, while light trucks improved somewhat from 18.2 mpg (1979) to 21.3 mpg. Since then, fuel economy has remained flat (figure 1).
Set by legislation, the Corporate Average Fuel Economy (CAFE) standard for new cars has been held constant at 27.5 mpg since 1990 (table 1). In 2000, the U.S. Congress asked the National Academy of Sciences to conduct a study, in consultation with the U.S. Department of Transportation, to evaluate the effectiveness and impacts of CAFE standards. A special National Research Council committee reported several findings and recommendations to Congress in 2001 but took no position on what the appropriate CAFE standards should be . Subsequent to the release of the report, the National Highway Traffic Safety Administration (NHTSA) announced that it was proceeding with rulemaking for the light truck fleet for model year 2004 and is updating its mid-1990s study on the relationship between fuel economy standards and safety . The passenger car standard remains at 27.5 mpg until Congress changes the current statute.
In recent years, efficiency gains have been offset by increases in vehicle weight and power and by consumer shifts to less efficient vehicles, such as light trucks, especially sport utility vehicles, minivans, and pickup trucks. For example, the average weight of new cars (foreign and domestic) rose from a low of 2,805 pounds in 1987 to 3,126 pounds in 2000. The average weight of new cars today is still lower than the 3,349-pound weight of new cars in 1978. Furthermore, in response to consumer demand for new high performance cars, the ratio of horsepower to 100 pounds of weight increased from 3.98 in 1987 to 5.27 in 2000. For the domestic car fleet, the average is 5.26 horsepower per 100 pounds .
The popularity of light trucks continues to grow. Twice as many cars as light trucks were sold in the United States in 1990. However, in 2001, retail sales of light trucks (8.7 million) for the first time surpassed car sales (8.4 million) . Clearly, many consumers are finding what they want in light trucks rather than cars: roominess, more carrying capacity, greater visibility, and a perception of safety (at least for themselves). However, this trend has implications for energy consumption and for emissions, because light trucks, on average, are less fuel-efficient than cars.
Using a different method of calculation, the U.S. Environmental Protection Agency (EPA) generates fuel economy data that are lower than the official CAFE averages (reported in figure 1). For 2001 model year light-duty vehicles, for instance, EPA estimated the average fuel economy to be 20.4 miles per gallon-the lowest in 21 years-and attributes the decline to the increasing market share of light trucks, plus overall increased vehicle weights and performance. If weight and performance attributes were similar to those in 1981, the 2001 fleet could have achieved more than 25 percent higher fuel economy .
1. National Research Council, Transportation Research Board, Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards (Washington, DC: National Academy Press, 2001).
2. U.S. Environmental Protection Agency, Light-Duty Automotive Technoloy and Fuel Economy Trends, EPA420-R-01-008 (Washington DC: September 2001).
3. U.S. Department of Transportation, Bureau of Transportation Statistics, Transportation Indicators, May 2002.
4. U.S. Department of Transportation, National Highway Traffic Safety Administration, statement of Jeffrey W. Runge, Administrator, before the Committee on Commerce, Science, and Transportation, United States Senate, Dec. 6, 2001.
5. U.S. Department of Transportation, National Highway Traffic Safety Administration, Automotive Fuel Economy Program, "Annual Update Calendar Year 2000," July 2001, available at http://www.nhtsa.dot.gov/cars, as of August 2000.
Most scientists believe that rising concentrations of greenhouse gases (GHGs) in the Earth's atmosphere could cause global climate change. GHGs, such as carbon dioxide, methane, and nitrous oxide, occur naturally and can be produced by human activities. Carbon dioxide is the predominant greenhouse gas produced by human activity, accounting for 83 percent of all U.S. GHG emissions in 2000. Nearly all carbon dioxide emissions are produced by the combustion of fossil fuels. Thus, there is a high correlation between energy use and carbon emissions .
Today, almost all of transportation's energy needs are supplied by oil. The combustion of petroleum in the transportation sector alone is responsible for about 27 percent of all GHGs emitted in the United States. From 1990 to 2000, emissions of carbon dioxide from transportation grew 19 percent (figure 1). This growth is less than that of the residential and commercial sectors (22 and 27 percent, respectively) but six times greater than in the industrial sector (3 percent). With emissions of 515 million metric tons of carbon in 2000, however, transportation leads all sectors.
On a modal basis, highway vehicles emit almost 80 percent of U.S. transportation's GHGs, and half of those come from passenger cars (table 1). Under the United Nations Framework Convention on Climate Change, to which the United States is a party, a nation's inventory of emissions does not include those stemming from international aircraft and ships. Thus, under the U.S. Environmental Protection Agency's method of estimating U.S. GHG emissions (see box), only domestic aircraft emissions are included in the breakdown by mode. With just 6 percent of emissions attributed to aviation, this mode ranks a distant second to highway vehicles.
The U.S. Department of Energy (DOE) has projected carbon dioxide emissions from energy use to grow 1.5 percent annually to 2,088 million metric tons of carbon equivalent (mmtce) by 2020. Transportation GHG emissions are expected to grow at a rate of 1.9 percent, just above the 1990 to 2000 growth rate of 1.8 percent. DOE based the transportation rate of growth on expected increases in vehicle-miles traveled and in freight and air travel, accompanied by only small gains in vehicle efficiency .
The Bush Administration announced new climate change policies in February 2002 . The administration plans to measure overall U.S. performance by tracking the greenhouse gas intensity of the U.S. economy (figure 2). The goal is to reduce the intensity by 18 percent by 2012. Between 1990 and 2000, the intensity declined by 17 percent, while emissions grew 14 percent and the economy grew 38 percent. To help meet its goal, the Administration has proposed two new research programs: The Climate Change Research Initiative and the National Climate Change Technology Initiative. The U.S. Department of Transportation's Center for Climate Change and Environmental Forecasting, established in 1999, identifies and evaluates options to reduce GHG emissions from and impacts on transportation.
1. U.S. Department of Energy, Energy Information Administration, Annual Energy Outlook 2002, DOE/EIA-0383(2002) (Washington, DC: December 2001).
2. The White House, "President Announces Clear Skies & Global Climate Change Initiatives," news release, Feb. 14, 2002, available at http://www.whitehouse.gov/news/releases/2002/, as of May 2002; and "Global Climate Change Policy Book," available at http://www.whitehouse.gov/news/releases/2002/02/climatechange.html/, as of May 2002.
Overall, most transportation air emissions have declined since 1980 despite significant increases in U.S. population, gross domestic product, and vehicle-miles traveled. For instance, carbon monoxide (CO), volatile organic compounds (VOC), particulates, and lead have decreased. These reductions are due primarily to vehicle tailpipe and evaporative emissions standards established by the U.S. Environmental Protection Agency (EPA), improvements in vehicle fuel efficiency, and the ban on leaded fuel for motor vehicles.
Only nitrogen oxide (NOx) emissions, which contribute to the formation of ground-level ozone, and ammonia remain above their 1990 level (figure 1). An increase in emissions from diesel vehicles is the leading factor in NOx growth and has led to new standards that will go into effect in 2004 . For instance, NOx emissions standards for newly manufactured gasoline- and diesel-powered heavy-duty trucks will be reduced from 4.0 to 0.20 grams per brake horsepower-hour in 2007 (diesel) and 2008 (gasoline). In addition, the existing standards for diesel particulates are being reduced from 0.10 to 0.01 grams per brake horsepower-hour in 2007. Gasoline-powered heavy-duty trucks will be subject to the same standard starting in 2008 .
Although progress has been made in reducing pollutants, transportation still accounts for a sizable percentage of several key pollutants. In 1999, for example, transportation contributed about 57 percent of all CO emissions, 45 percent of NOx, 37 percent of VOC, and 12 percent of lead  (see box 2). With the exception of lead, highway vehicles were the primary transportation source of these pollutants. The use of lead in aircraft fuel is responsible for nearly all transportation lead emissions. Figure 2 shows 1999 emissions by mode.
In 1997, EPA added ammonia to its National Emission Inventory. Gaseous ammonia reacts in the air with sulfur dioxide and NOx to form ammonium sulfate and nitrate particles that are found in particulate matter of 2.5 microns in diameter or smaller. In 1999, transportation, primarily highway gasoline-powered vehicles, accounted for about 5 percent of total ammonia emissions.
See box 1 to see Data on Toxic Air Pollutants.
Failures in transportation systems (vessels, pipelines, highway vehicles, and railroad equipment) or errors made by operators can result in spills of oil and hazardous materials. Better information is available about the extent of spill incidents than about the overall consequences of these spills on the environment and human health. The impact of each spill, for instance, will depend on the concentration and nature of the pollution, the location and volume of the spill, weather conditions, and the environmental resources affected.
When an oil spill occurs in U.S. waters, the responsible party is required to report the spill to the U.S. Coast Guard. The Coast Guard collects data on the number, location, and source of spills, volume and type of oil spilled, and the type of operation that caused spills. Between 1996 and 2000, an annual average of 1.5 million gallons of various types of oil were spilled by all sources (figure 1).
The total amount, source, and type of oil spilled varies each year (table 1). For instance, marine vessels and pipelines were responsible for 73 percent of the spills (by volume) reported in 2000, but just 40 percent in 1991 . Much of the oil spilled tends to be cargo, but that too varies by year. It amounted to 51 percent of the volume of oil spilled in 1998 but just 24 percent in 1999 [1, 2]. New research suggests that, on an annual average basis, transportation of petroleum results in only a small portion of the petroleum that enters North American ocean waters each year (see box).
The largest oil spill in 2000 (and the largest since 1996) occurred when a tanker grounded in the Mississippi River, resulting in the loss of 538,000 gallons of crude oil from one of its cargo tanks. The largest pipeline incident in 2000 was a leak of about 175,000 gallons of oil into a tributary of the Delaware River .
1. American Petroleum Institute, Oil Spills in U.S. Navigable Waters: 1989-1998 (Washington, DC: Feb. 22, 2000).
2. _____. Oil Spills in U.S. Navigable Waters: 1990-1999 (Washington, DC: Jan. 18, 2001).
3. U.S. Department of Transportation, U.S. Coast Guard, Pollution Incidents In and Around U.S. Waters, A Spill Release Compendium: 1969-2000, available at http://www.uscg.mil/hq/, as of March 2002.
The nation's ports and navigation channels must be regularly dredged to maintain proper depths to accommodate shipping. The environment is affected in two ways by dredging. First, the dredging activity can, for instance, cause entrainment of fish eggs and larvae, resuspension of buried contaminated sediments, habitat loss, and collisions with marine mammals. To reduce the risks to biological resources, the U.S. Army Corps of Engineers imposes "environmental windows" on 80 percent of all federal dredging projects. Dredging is allowed to proceed during these windows, periods when adverse impacts are reduced below critical thresholds .
The other environmental impact of dredging is disposal of dredged sediments, especially when they are contaminated. The U.S. Environmental Protection Agency estimated that 3 million to 12 million cubic yards of material dredged each year are sufficiently contaminated to require special handling and disposal . A more recent report on U.S. coastal waters concluded that, while it varies by region, 35 percent of the nation's total estuarine surface area contains contaminated sediments . Contaminants include hydrocarbons, polychlorinated biphenyls (PCBs), pesticides, and metals.
National data, which the Corps aggregates on an annual basis from individual dredging contracts, do not identify how much material is contaminated, although the data show how dredged material is managed (figure 1). Several of the reporting categories (especially confined, open water/upland, and mixed) may include contaminated sediments.
Dredging U.S. navigable waterways, the Corps produced 285 million cubic yards of materials at a total cost of $822 million in fiscal year 2000 . Dredging costs per cubic yard remained fairly stable from 1990 to 1997 (figure 2). They rose 38 percent in 1998 but by 2000 had fallen back to about 23 percent above 1997. Environmental considerations can affect dredging costs. Environmental windows have cost implications as do disposal requirements. For instance, a rise in the proportion of contaminated materials in any one year can affect that year's total costs.
U.S. port authorities are responsible for dredging their berths and channels. They spent $117 million, 11 percent of their capital expenditures, on dredging in 2000 . Data on disposal methods and the total amount of material dredged by ports are only occasionally available.
1. Transportation Research Board, Marine Board, A Process for Setting, Managing, and Monitoring Environmental Windows for Dredging Projects, Special Report 262 (Washington, DC: National Academy of Sciences, 2001).
2. U.S. Army Corps of Engineers, Water Resources Support Center, Navigation Data Center, Dredging Information System, available at http://www.wrsc.usace.army.mil/ndc/drgmatdisp.htm, as of April 2002.
3. U.S. Department of Transportation, Maritime Administration, Office of Ports and Domestic Shipping, United States Port Development Expenditure Report (Washington, DC: December 2001).
4. U.S. Environmental Protection Agency, National Coastal Condition Report, EPA-620/R-01/005 (Washington, DC: September 2001).
5. U.S. Environmental Protection Agency, Office of Water, EPA's Contaminated Sediment Management Strategy, EPA-823-R-98-001 (Washington, DC: April 1998).
Underground tanks for storing petroleum products, such as fuels for transportation, have a history of leaking petroleum into the nation's underground water. The U.S. Environmental Protection Agency (EPA) started collecting annual data on the problem and its resolution in fiscal year (FY) 1990 under the Underground Storage Tank Program.
By the end of FY 2001, EPA regions reported that there were 704,717 active underground tanks in the nation and that 1.5 million tanks had been closed . Between 1990 and 2001, the number of confirmed releases1 of petroleum from underground storage tanks (USTs) climbed at an average annual rate of 21 percent, while cleanups were completed at a rate of 29 percent per year (table 1). However, cleanups had not been initiated for nearly 39,700 releases. In addition, the U.S. General Accounting Office estimated that 29 percent of the new tanks were not being maintained and operated properly to prevent them from leaking .
As with oil spills in U.S. waters, these data do not reveal the overall environmental impact of releasing petroleum products into underground and surface waters. Furthermore, the data gathered show the number of incidents rather than volume; thus, even the full extent of the problem is not clear. For example, the amount of water contaminated by releases from underground tanks is not known. Petroleum products are also stored in aboveground tanks. However, no national data exist on numbers of incidents or volumes released from these tanks.
In 2000, concern arose about the leaking of methyl-tertiary-butyl-ether (MTBE) from storage tanks and other sources. MTBE is a constituent of reformulated gasoline, which is used in nonattainment areas of the country to improve air quality. Once released, MTBE moves rapidly through underground water. This substance has been detected in drinking water, with the highest levels in areas of the country using reformulated gasoline. Leaking USTs appear to be a major source of groundwater contamination from MTBE, but other sources include aboveground tanks, pipelines, and recreational boats . Various efforts are underway or proposed in 13 states, the U.S. Congress, and EPA to reduce or ban the use of MTBE as an oxygenate in reformulated gasoline. California has, however, delayed its ban on MTBE for one year to the end of 2003. Ethanol, the alternate oxygenate, holds a much smaller share of the current national market (see the section on Alternative and Replacement Fuels in this chapter), and the state will have to create a new infrastructure to assure a sufficient supply of this type of reformulated gasoline.
1A confirmed release is an identified incident and is not necessarily equivalent to the number of leaking underground storage tanks at any one site (e.g., a gasoline station).
1. U.S. Environmental Protection Agency, Achieving Clean Air and Clean Water: The Report of the Blue Ribbon Panel on Oxygenates in Gasoline, Executive Summary and Recommendations (Washington, DC: July 27, 1999).
2. U.S. Environmental Protection Agency, Office of Underground Storage Tanks, Corrective Action Measures Archive, available at http://www.epa.gov/swerust1/cat/camarchv.htm, as of April 2002.
3. U.S. General Accounting Office, Environmental Protection: Improved Inspections and Enforcement Would Better Ensure the Safety of Underground Storage Tanks, GAO-01-464 (Washington DC: May 4, 2001).
Transportation equipment and infrastructure eventually become wastes. For instance, over 11.6 million passenger cars and trucks were scrapped in 1999 . Additional wastes are generated as equipment (e.g., vehicles, aircraft, vessels, and locomotives) and parts are repaired during their lifetime. Scrapped equipment is generally dismantled, with some parts or materials recycled and the rest disposed. Fluids, such as used motor oils and refrigerants, may be regenerated or disposed. Improper disposal of any of these materials or fluids can pose environmental problems. Used tire piles can ignite, releasing toxic chemicals into the air. Oil can contaminate water bodies.
There are few data on the extent of transportation wastes created annually. Overall, people in the United States generated an estimated 230 million tons of municipal solid waste in 1999 . Tires and batteries from passenger cars, trucks, and motorcycles contributed 6.6 million tons to this total (figure 1 and figure 2). The balance of transportation wastes, such as equipment, other batteries and tires, discards from dismantling operations, and motor oils, are not included, nor are infrastructure construction debris.1
The recovered portion of lead-acid batteries and tires is reused in some form and therefore does not end up in waste landfills or incinerators. Batteries are dismantled and 97 percent of the lead content and a significant portion of the polypropylene casing were recycled in 1999. Only 26 percent (by weight) of tires were recycled, however.
The transportation sector used an estimated 1,260 million gallons of lubricants in 1999, 50 percent of the lubricants consumed by all sectors that year . Motor oils become wastes throughout a vehicle's lifecycle and may be burned as fuel, placed in landfills, rerefined, or incinerated. In addition, some are illegally dumped. The amount of waste motor oils generated each year and how it is disposed are estimated only periodically. About 250 million gallons of motor oil were recycled in 1997 .
1The Federal Highway Administration issued a Formal Policy on the Use of Recycled Materials in highway applications in February 2002.
1. American Petroleum Institute, "Used Motor Oil: Collection and Recycling," available at http://www.recycleoil.org/Usedoilflow.htm, as of March 2002.
2. U.S. Department of Energy, Energy Information Administration, State Energy Data Report 1999, tables 11 and 15, available at http://www.eia.doe.gov/emeu/sedr/contents.html#PDF Files/, as of March 2002.
3. U.S. Department of Transportation, Bureau of Transportation Statistics, National Transportation Statistics 2000 (Washington DC: 2001), table 4-54.
4. U.S. Environmental Protection Agency, Municipal Solid Waste in the United States: 1999 Facts and Figures, EPA530-R-01-014 (Washington, DC: July 2001).
Wetlands provide many environmental benefits. They serve as wildlife habitats and spawning grounds for fish, provide vast amounts of food for aquatic species, and help remove organic pollutants from bodies of water. Yet, it is only during the last few decades that the United States has considered wetlands a natural resource worth enhancing and preserving. This change in thinking occurred after an estimated half of the wetlands acreage believed to exist in the 1600s had been drained . By 1997, the nation had an estimated 105.5 million acres of wetlands, having suffered a net loss of almost 650,000 acres of wetlands between 1986 and 19971 .
Transportation infrastructure and its use has contributed to the loss of wetlands, but it is unclear to what extent. For instance, when the Fish and Wildlife Service made their 1997 estimates, transportation activities were not reported separately but considered part of urban development, a category accounting for an estimated 30 percent of all wetland losses. Because federal policy requires compensatory mitigation to restore, create, or enhance impacted wetlands, developers of roads, airports, rail systems, and marine facilities must determine whether their projects will affect wetlands. If so, they may need to obtain a Clean Water Act Section 404 permit from the U.S. Army Corps of Engineers.
The only national trend data on transportation wetlands impacts have been collected, since 1996, by the Federal Highway Administration (table 1). These data cover wetlands acreage affected by federal-aid highways, which constitute 24 percent of the total miles of public roads in this country . Although the Federal Aviation Administration (FAA) does not collect data on wetlands impacted by airports, airport runway expansion often involves an evaluation of those effects. FAA is particularly concerned that mitigation projects do not create habitats that would attract wildlife known to affect aircraft operations.
Some of the sediments the U.S. Army Corps of Engineers dredges from navigation channels are used to nourish wetlands. The amount varies each year; in fiscal year 2000, the Corps applied 96 million cubic yards of sediment to wetlands . This was just over 4 percent of all Corps-dredged material that year compared with 16 percent (39 million cubic yards) in 1998.
While the available data provide some insight into transportation infrastructure's relative effect on wetlands, there are no data on impacts from runoff of salt, oils, and rubber from highways and other facilities, and air pollutants emitted by vehicles, locomotives, airplanes, and vessels as they move along or through wetland areas. Furthermore, acreage data provide no information on the quality of wetlands as measured by their value to society .
1This amounts to an average annual rate of loss of 58,500 acres, according to the Fish and Wildlife Service. An alternate source of wetlands data-the U.S. Department of Agriculture, Natural Resources Conservation Service-has estimated an average annual loss of 32,600 acres between 1992 and 1997.
1. U.S. Army Corps of Engineers, Dredging Information System, available at http://www.wrsc.usace.army.mil/ndc/dcgmatdisp.htm, as of March 2002.
2. U.S. Congress, Congressional Research Service, "Wetlands Issues," Aug. 7, 2001.
3. U.S. Department of the Interior, Fish and Wildlife Service, Status and Trends of Wetlands in the Conterminous United States: 1986 to 1997 (Washington, DC: December 2000).
4. U.S. Department of Transportation, Federal Highway Administration, Highway Statistics 2000 (Washington, DC: 2001), table HM-14.
5. U.S. Environmental Protection Agency, Office of Water, "What are Wetlands? Status and Trends," available at http://www.epa.gov/owow/wetlands/vital/status.html, as of March 2002.
Indicators are quantitative data that can be used to assess the magnitude of problems, help set priorities, develop performance measures and track progress toward goals, or educate stakeholders. To assess problems and measure progress, trend data are needed. The full range of environmental effects of the transportation system is extensive but few good indicators are available.
Figure 1 is a conceptual diagram of the environmental effects of transportation from a lifecycle perspective. Phases (or stages) of transportation include fuel production, vehicle manufacturing, fixed infrastructure development, travel (or vehicle use), maintenance, and disposal. Activities occurring during the phases result in environmental outcomes (e.g., pollution releases and changes in wetlands acreage). Outcomes can, in turn, affect the environment and human health, creating impacts that are usually negative (e.g., cancers, birth defects, asthma, stunted tree growth, and fish kills). Impacts, which can be chronic or acute, are highly dependent on two variables: concentration and exposure.
Activity, outcome, or impact data can be the source for indicators. However, outcome indicators are most commonly used for transportation. Activities are only indirectly related to environmental consequences. Increases in passenger car vehicle-miles traveled may or may not result in increased pollutant releases. Similarly, the volume of oil transported by marine vessels is not indicative of harm caused by oil spills at sea. Most available impact data do not directly identify sources, such as transportation. For instance, the U.S. Environmental Protection Agency (EPA) reports annually on changes in the nation's air quality. These data come from monitoring stations that measure concentrations of pollutants in the atmosphere. The sources of the pollutants may be factories, powerplants, dry cleaning facilities, printing shops, storage tanks, and so on, as well as vehicles.
Readily available data for outcome indicators are not comprehensive, especially for all modes and lifecycle phases. National trend data for outcomes are estimated, modeled, or collected only for some pollutants.
The most often used transportation environmental indicator comprises six criteria air pollutants regulated under the Clean Air Act (see Introduction). The data are estimated annually by EPA and show the relative outcome contribution of these pollutants by mode (except pipelines) during the travel phase. With the emergence of the global climate change issue, an additional indicator is available. EPA and the Energy Information Administration, U.S. Department of Energy, now annually estimate the amount of six greenhouse gases emitted by the transportation sector.