The U.S. transportation system is a vast enterprise. Transportation-related goods and services account for about one tenth of the nation's gross domestic product, and the economy relies heavily on the low-cost, highly flexible movement of goods and services. Most Americans enjoy a level of personal mobility that offers them a wide range of choices about where to live, work, shop, obtain health care, and vacation.

Yet, not all the costs of mobility are paid directly by the individuals and businesses who are the beneficiaries. Transportation has a significant impact on environmental quality in a wide variety of ways, notably in terms of air quality, land use and development, habitats and open space, and energy use.

Particularly notable is the high dependence of most American communities on the automobile as the principal means of transportation. Urban growth has often been characterized by new housing developments encroaching farther into agricultural and environmentally sensitive lands, an increasing dependence on automobiles, and the isolation of central cities and older communities. Many states have been struggling to reverse these trends.

TRENDS

Transportation Infrastructure

The nation's transportation network -- its system of roads, bridges, rail, airports, and ports -- continues to expand and improve, except for a few exceptions. Highlights of the trends over the last two decades (1980-1998, unless otherwise noted) are presented below.

Road Mileage and Conditions. Public road mileage increased by 2.5 percent, bringing the total to nearly 4 million miles, while lane-miles grew by 3.4 percent to total 8.2 million miles as many roads expanded from two to four lanes or more. Paved roadways now constitute about 61 percent of all highway mileage, up from only 30 percent four decades ago (Figure 10.1), and pavement surface conditions have improved, reversing the downward trend in physical condition that was evident in the 1970s and early 1980s. In 1987, 76 percent of urban highway miles and 84 percent of rural highway miles were in fair or better condition (i.e., will not require improvement in the near future).

Bridge Conditions. The condition of U.S. bridges has improved noticeably since 1990. In 1997, 70 percent of the nation's 582,751 bridges were in good condition, up from 58 percent in 1990. Seventeen (17) percent of the bridges in 1997 were structurally deficient while 13 percent were functionally deficient.

Freight Rail. Class I freight railroads account for 71 percent of the industry's 171,285 miles operated. Since 1980, Class I railroads increased their traffic by 47 percent, while their network (miles owned) declined by 38 percent due to sale of track to smaller railroads or abandonment. As a result, traffic density on existing track has increased, requiring railroads to double, triple or quadruple their tracks in high density corridors.

Passenger Rail. Between 1984 and 1996, the number of stations served by Amtrak increased from 510 to 542 while those served by rail transit increased from 1,822 to 2,587. The number of stations for both types of passenger rail has declined since then

Airports. Airway system mileage increased from 341,000 miles in 1980 to 394,000 in 1995 (no estimates are available for years since then). In 1997, the United States had 18,345 airports,a 20 percent increase compared with 1980. The addition of 3,200 general aviation airports accounts for much of the increase. The condition of runway surfaces improved overall, especially at airports not regularly served by commercial carriers. Runways in good condition rose form 61 percent in 1986 to 72 percent in 1997.

Ports and Waterways. In 1997, over 2 billion tons of foreign and domestic waterborne commerce was handled by 3,726 marine terminals. These terminals are about equally divided between deep-draft (ocean and Great Lakes) and shallow-draft (inland waterways) facilities. Most inland facilities (86 percent) are used for transporting bulk commodities, while coastal facilities transport both bulk commodities (41 percent) and general cargo (38 percent). In the near future, many coastal facilities may need to deepen channels and berth depth and expand/improve terminal and transportation infrastructure to accommodate the next generation of container ships and their increased cargo.

Oil and Gas Pipelines. Although comprehensive data are not available, it appears that oil and gas pipeline mileage remained stable in the 1990s. In 1997, oil and gas transportation pipelines extended over an estimated 500,000 miles.

Transportation Vehicles

The number of vehicles used in transportation -- cars, trucks, buses, railcars, aircraft, boats, and ships -- also continue to increase. Some trends are as follows.

Highway Vehicle Fleet. The nation's highway vehicle fleet -- automobiles, buses, and trucks -- consisted of about 216 million vehicles in 1998, nearly double the number of vehicles in 1970. Of special note has been the dramatic growth in the number of sport utility vehicles (SUVs) and other light trucks. This segment of the fleet increased from 14 million vehicles in 1970 to nearly 72 million in 1998 and now accounts for 33 percent of the fleet (Figure 10.2). Still, passenger cars accounted for 61 percent of the total highway fleet, despite a 5 million vehicle decrease in the number of automobiles over the past decade.

Large trucks and buses show a more moderate increase. Registrations of 2-axle single-unit trucks with 6 tires or more grew from 3.7 million in 1970 to 5.4 million in 1998, and combination truck registrations increased from 0.91 million to 1.8 million. Bus registrations grew from 377,562 to 715,540 over the period (Figure 10.3).

Aircraft. The number of air carriers increased from 2,679 in 1970 to 7,616 in 1997. The active general aviation fleet increased from 131, 743 in 1970 to 205,000 in 1989, declined between 1989 and 1994 (to 172, 000 aircraft), and then increased to 192,000 in 1997.

Boats. The number of both commercial and recreational boats continues to increase. In 1997, the U.S.-flag commercial vessel fleet was over 41,400, up from 38,800 in 1980. Approximately 12.3 million recreational boats were registered in the United States in 1997 compared to 7.4 million in 1970. An unknown number of other boats are not registered.

Transportation System Use

Both passenger travel and freight transportation have grown considerably over the past three decades. Growth has been seen most transportation modes.

Highway Travel. Annual travel on the nation's highways reached an estimated 2.63 trillion vehicle-miles in 1998, or about three times the level in 1960. Travel grew about 47 percent during the 1960s, another 38 percent in the 1970s, and another 37 percent in the 1980s. One result of this growth has been greater congestion in the nation's urban areas (Figure 10.4). The most dramatic increase in travel has been by other 2-axle, 4-tire vehicles with an increase of 561 percent since 1970. This rapid increase is due to the popularity of pickup trucks, sport utility vehicles, and minivans.

Personal Travel. According to the National Personal Transportation Survey, Americans averaged 4.3 one-way trips per day and about 14,100 miles per year (or 39 miles per day) in 1995 (the latest year for which data are available), up from 2.9 trips and 9,500 miles (26 miles per day) in 1977. Long-distance travel (trips 100 miles or more from home) increased over this period from 2.5 roundtrips in 1977 to 3.9 in 1995. Several factors account for this increase in travel, including greater labor force participation, income, and vehicle availability, and reduced travel costs.

Other Modes of Passenger Travel. Air travel, in terms of passenger emplanements and passenger-miles flown, more than doubled between 1980 and 1997. Transit ridership remained relatively constant at around 40 billion passenger-miles over the period. (Passenger-miles represents the total distance traveled by all passengers in passenger cars, airplanes, transit, rail and other modes; one passenger traveling one mile generates one passenger-mile). Riders on buses and heavy rail constitute the majority of transit users, but ridership on these modes stagnated over this period, while the number of riders on other transit modes -- especially demand response service, light rail, and ferries -- increased markedly. Ridership on commuter rail increased a moderate amount, while passenger rail travel on Amtrak remained relatively constant.

Freight. All freight modes showed an increase in ton-miles transported between 1970 and 1997. (Ton-miles are defined as the movement of one ton of freight for a distance of one mile. Ton-miles are computed by multiplying the weight in tons of each shipment transported by the distance hauled.) Shipments by domestic air carriers rose from 2.7 billion ton-miles to 13.6 billion tons-miles over the period, while truck shipments grew from 412 billion ton-mile to 1 trillion ton-miles. Rail ton-miles nearly doubled, while ton-miles on domestic waterways increased from 1970 to 1980 and then leveled off. Foreign waterborne commerce quadrupled between 1959 and 1998 (Figure 10.5).

Transportation and the Environment

Some serious environmental issues continue to be associated with transportation.

Emissions

The use of petroleum is responsible for most of the environmental problems, including emissions of carbon dioxide that may contribute to climate change and emissions of criteria air pollutants and air toxics. In 1998, transportation sources running on petroleum emitted 471.5 million metric tons of carbon into the atmosphere; this represented about 32 percent of the total annual U.S. CO2 emissions. Emission control technology installed in motor vehicles has resulted in lower emissions of CO and VOC despite the rapid growth in vehicle activity over the past two decades, and use of lead-free gasoline has nearly eliminated vehicular lead emissions. Transportation is also a contributor to the depletion of the stratospheric ozone layer. Mobile air conditioning systems in many vehicles emit chlorofluorocarbons and other chemicals that are harmful to the ozone layer.

Energy Use

The U.S. transportation system is about 95 percent petroleum dependent, down about two percentage points from a decade ago. In 1998, transportation-driven oil demand together with declining domestic production brought about the highest levels of oil imports ever (48 percent of oil use). Transportation is the only sector of the economy that consumes significantly more petroleum today than it did in 1973, the first year of the oil price shock. Highway vehicles continue to dominate transportation energy use. Light-duty passenger vehicles alone account for over 60 percent of all energy used in transportation.

Average gas mileage for passenger cars has stayed about the same in the 1990s -- about 20-21 miles per gallon. Since 1960, gains are impressive. For passenger cars, fuel efficiency per vehicle has increased from 14.3 miles/gallon in 1960 to 21.4 miles/gallon in 1998 (Figure 10.6). From 1973 to 1998, the average fuel efficiency of new passenger cars entering the fleet increased from 14.2 mpg to 28.5 mpg. Some of the gains in car fuel efficiency were offset by a shift in the composition of private vehicle usage towards light-duty trucks and sport-utility vehicles. (Fuel consumption per vehicle is the ratio of vehicle-miles traveled to total gasoline consumption (in gallons).

Aircraft Noise

In the late 1960s, Congress directed the Federal Aviation Administration to begin regulating aircraft noise, establishing the first federal noise standards for new-design turbojet and transport category jet aircraft. These "Stage 2" aircraft noise standards were subsequently applied to all newly produced planes, including those of older designs.

These steps did not fully solve the problem; by 1974, FAA estimated that 7 million people were still severely affected by aircraft noise. In 1976, FAA required that all subsonic aircraft in operation meet Stage 2 requirements by January 1, 1985. In 1977, FAA implemented more stringent Stage 3 noise standards for new aircraft, and by 1998, there was more than a 4 percent increase over the past year in the number of noise-certified aircraft (Stage 3 fleet mix), thus helping to lessen the noise problem in some communities.

Scrap Tire Disposition

Disposal of scrap tires has been an environmental problem for many decades; the nation annually throws away about 250 million scrap tires, many of which go to landfills, scrap tire stockpiles, or illegal dumps.

The scrap tire problem has changed quited dramatically over the past several years, largely as a result of a significant increase in their use as tire-derived fuel. From 1990 to 1996, the number of tires used as fuel increased nearly five-fold, reaching more than 150 million. Demand for scrap tires in other markets also roughly doubled during this period. These markets include ground rubber applications, such as asphalt products, new tires, bound rubber products, and athletic surfaces; civil engineering applications, such as fill material, road bed material, and aggregate; and other applications such as artificial reefs, playground equipment, and crash barriers.

With the growth of these important new markets for scrap tires, EPA and the Scrap Tire Management Council estimate that the number of scrap tires stockpiled, landfilled, and dumped annually may have fallen by as much as two thirds.

References

U.S. Army Corps of Engineers, 1999 Waterborne Commerce of the United States (USACE, Washington, DC, 2000). (http://www.wrsc.usace.army.mil/ndc/wcsc.htm)

U.S. Department of Transportation, Federal Highway Administration, Highway Statistics 1999 (DOT, FHWA, Washington, DC, 2000). (http://www.fhwa.dot.gov/ohim/ohimstat.htm)

--, Summary of Travel Trends: 1995 Nationwide Personal Transportation Survey (DOT, FHWA, Washington, DC, 1999). (http://www.bts.gov/ntda/npts/)

U.S. Department of Transportation, Bureau of Transportation Statistics, National Transportation Statistics 1999 (DOT, BTS, Washington, DC, 2000). (http://www.bts.gov/btsprod/nts/)

--, Transportation Statistics Annual Report 1999 (DOT, BTS, Washington, DC, 2000). (http://www.bts.gov/programs/transtu/tsar/tsar.html)

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