Chapter One - System Extent and Condition
Chapter One - System Extent and Condition
The U.S. transportation system makes possible a high level of personal mobility and freight activity for the nations 268 million residents and nearly 7 million business establishments. In 1997, they had at their disposal over 230 million motor vehicles, transit vehicles, boats, planes, and railroad cars that circulated over 4 million miles of highways, railroads, and waterways connecting all parts of the United States, the fourth largest nation in land area. The transportation system also includes over 500,000 miles of oil and gas transmission pipelines (enough pipeline to circle the earth nearly 20 times), 18,000 public and private airports (an average of about 6 per county), and transit systems offering half the urban population access to a transit route within one-quarter mile of their home. In addition to traditional infrastructure components, advanced communications and information technologies are emerging as integral parts of transportation systems. These technologies help people and businesses use transportation more efficiently by providing the capability to monitor, analyze, and control infrastructure and vehicles, and by providing real-time information to system users.
In 1997, passenger-miles of travel in the United States totaled approximately 4.4 trillion. Americans averaged 39 miles of local travel per day in 1995, roughly the straight-line distance between Baltimore and Washington, DC. If summed up for the entire year, the local and long-distance travel-miles of the typical American would extend more than halfway around the world. As for freight, preliminary estimates by the Bureau of Transportation Statistics (BTS) show that domestic commodity shipments in 1997 produced 3.9 trillion ton-miles of activity, 10 percent more than in 1993. (The estimate is based on the Commodity Flow Survey conducted in both years by BTS and the Census Bureau, plus additional data on underrepresented movements).
This chapter discusses the physical extent and condition of the nations transportation system, updating information in previous editions of the Transportation Statistics Annual Report (TSAR). Table 1-1 provides a snapshot of the key elements of the transportation system by mode. Where information is available, the chapter reports on the operating condition of transportation vehicles and the infrastructure they use. The topics in this chapter are presented by mode, except for a discussion of intelligent transportation system (ITS) components, because ITS is multimodal in nature. This years report profiles in more detail the extent and condition of the rail transportation system (prior editions of the TSAR focused on domestic water transportation, urban transit, and commercial aviation). The rail profile includes discussion of the status of high-speed rail projects in the United States and use of information technology by railroads to improve safety. Trends in passenger travel, freight movement, and transportation system performance are discussed in chapter 2.
In the United States, public roadsan extensive network that ranges from unpaved farm roads to 16-lane freewayscarry over 90 percent of all passenger trips and over half the freight tonnage. The number of miles of public roads has increased year by year, but by small amounts in relation to the overall size of the system (See figure 1-1). Between 1987 and 1997, about 55,000 miles of public roads were added to the system, increasing total miles to 3.94 millionless than a 2.0 percent increase over 10 years. The size of the highway system in urban areas grew more, by about 15 percent since 1987, although much of the growth was due to changes in classification rather than construction of new mileage (USDOT FHWA 1997, table HM-20; USDOT FHWA Annual editions, table HM-20). The growth in urban mileage is due primarily to expanding urban boundaries and additional areas being defined as urban, and not to highway construction. Even though public road mileage is relatively static, the number of lane-miles of highways has risen as roads are expanded from two lanes to four or more. There were nearly 61,000 new lane-miles added in 1997 alone, bringing the total to around 8.24 million (USDOT FHWA 1998a, table HM-60).
Paved roadways constituted about 61 percent of all highway mileage in 1997, up from 56 percent in 1987. Nearly all of the public roads in urban areas are paved. However, about half the miles of rural public roads are unpaved, accounting for 98 percent of total unpaved public road milesmuch the same ratio as in 1987 (USDOT FHWA Annual editions, table HM-51). The quality of roads is more difficult to evaluate than their extent. Furthermore, long-term trends in the condition of the nations roads are particularly hard to assess because the Federal Highway Administration (FHWA) has been in the process of changing to a different assessment methodology. In 1993, FHWA began using a road quality measure called the International Roughness Index (IRI) to evaluate part of the highway system: the so-called higher functional-class roadways, consisting of urban and rural Interstates, freeways, expressways and other principal arterials, and rural principal and minor arterials. The IRI shows moderate improvement in pavement conditions on these highways in both urban and rural areas between 1994 and 1997. The percentage of these roadways in fair or better condition increased, although in 1997 conditions on urban roadways classified as other principal arterials decreased slightly.
An older index, the Present Serviceability Rating (PSR), continues to be used to assess conditions for other highway functional classes (rural major collectors, urban minor arterials, and urban collectors) and to provide historical data for all classes prior to 1993. In 1997, 561,000 miles of highway were reported in these categories, whereas the number of miles assessed by the IRI was 316,000. The overall condition of urban minor arterials (as measured using the PSR) worsened a bit from 1994 to 1997 (see table 1-2), and the condition of urban collectors improved very little. The percentage of rural major collectors in fair or better condition improved from 71.5 percent in 1994 to 79.9 percent in 1997. However, the reported number of miles of rural major collector dropped 10.4 percent between 1994 and 1997, making it unclear whether conditions actually improved (USDOT FHWA Annual editions, tables HM-63 and HM-64; USDOT BTS 1998, table 1-38).
The condition of U.S. bridges has improved noticeably since 1990 (see table 1-3). Of the 583,000 bridges in operation in 1997, about 30 percent were either structurally deficient or functionally obsolete compared with over 41 percent in 1990. In general, bridges on roads in higher functional classes, such as Interstates and other principal arterials, are more likely to be structurally sound than are those on lower functional classes, such as collectors and local roads. Except for bridges on local roads, a higher percentage of rural bridges are structurally and functionally sound compared with their urban counterparts (USDOT FHWA 1998b).
The nations highway vehicle fleet consisted of about 2 1/2 million vehicles in 1997, nearly 28 million more vehicles than a decade earlier. The composition of vehicles in the fleet changed as more people bought pickup or other light trucks, sport utility vehicles (SUVs), and vans (see figure 1-2). These vehicles share of the fleet increased from 22 percent in 1987 to 33 percent in 1997, when there were over 70 million registered light trucks, SUVs, and vans. The number of registered automobiles fell from its historic high of 135 million in 1989, but the nearly 130 million automobiles in use in 1997 still accounted for about 61 percent of the highway vehicle fleet (USDOT FHWA 1997).
The total number of larger single-unit trucks (large trucks on a single frame with at least 2 axles and 6 tires), combination trucks (power unitstrucks or truck tractorsand one or more trailing units), and buses increased over the decade. Registrations of 2-axle single-unit trucks with 6 tires or more grew from 4.2 million in 1987 to 5.3 million in 1997, and combination truck registrations increased from 1.5 million to 1.8 million. Bus registrations grew from 602,000 to 698,000 during this period.
Motorcycle registrations declined, dropping from 4.9 million to 3.8 million over the same decade--a 22 percent decrease (USDOT FHWA 1997).
According to the 1995 Nationwide Personal Transportation Survey, nearly 92 percent of all households in the United States owned at least one vehicle in that year, with an average of about 1.8 vehicles per household. Households without at least one vehicle fell from about 11.5 million (15 percent of all households) in 1977 to about 8 million (8 percent of households) in 1995. Nearly one-fifth of low-income households (those earning less than $25,000 per year) had no vehicle in 1995 (ORNL 1999, 7, 9, 28, 29).
The cars and trucks driven in the United States are older now, on average, than a decade or so ago. The median age of an automobile in 1997 was 8.1 years, compared with 6.9 years in 1987 and 5.6 years in 1977. Median truck age increased to 7.8 years in 1997, compared with 7.6 in 1987 and 5.7 in 19771 (Polk 1999; USDOT BTS 1998, table 1-37). Although it is the only national indicator available, age is not necessarily a good indicator of vehicle condition, as the median age of vehicles is affected by many factors, including changes in vehicle quality, vehicle costs, and overall economic conditions.
In 1997, there were nine Class I freight railroads (railroads with operating revenues of $256.4 million or more) in the United States. These railroads accounted for 71 percent of the industrys 171,285 miles operated, 89 percent of its approximately 201,000 employees, and 91 percent of its $35.3 billion in freight revenue. There were 34 regional railroads (those with operating revenues between $40 million and $256.4 million and/or operating at least 350 miles of road). The regional railroads operated 21,466 miles, had about 11,000 employees, and earned $1.6 billion in freight revenue. There were 507 local railroads (falling below the regional railroad threshold, and including switching and terminal railroads) operating over 28,149 miles of road. They had slightly under 12,000 employees and earned $1.4 billion in freight revenue (AAR 1998, 3).
These freight railroads maintain their tracks, rights-of-way, and fleets of railcars and locomotives. Over the years, through mergers and rationalization of their physical plants, many little-used lines were abandoned or sold to smaller railroads. Since 1980, the Class I railroads increased their traffic (measured in ton-miles) by 47 percent, while their network (miles of road owned) declined by 38 percent (AAR 1998, 6, 44). Traffic density increased as traffic was concentrated over a smaller network. Because of this increased density, some railroads expanded capacity in their highest density corridors by double-tracking, such as was done by CSX in Ohio in the last few years. In some cases, railroads have even tripled or quadrupled their track on stretches of rail line where traffic is very heavy.
As for passenger rail, the National Railroad Passenger Corporation, more widely known as Amtrak, has operated a national passenger system since May 1971. Amtrak was created by the Rail Passenger Service Act of 1971 . . . to operate a national rail passenger system which ties together existing and emergent regional rail passenger service and other intermodal passenger service. During fiscal year (FY) 1998 (October 1, 1997 to September 30, 1998), Amtrak operated more than 250 intercity trains per day along a 22,000 route-mile railroad network in 44 states with service to more than 500 communities. In FY 1998, Amtrak carried 21.1 million intercity passengers, generating a total of 5.3 billion passenger-miles (up from FY 1996 and FY1997, but still below other years in the 1990s) and 54 million commuters carried under contract with transit authorities (NRPC 1998, 4750). Amtrak also relies on an extensive feeder bus network to carry rail passengers to and from off-line locations.
Over the past several years, Amtrak has ordered and taken delivery of about 200 bi-level Superliners (designed to replace aging Heritage equipment) and 50 Viewliners servicing the Midwest and the East Coast). The Viewliners are the first single-level sleeping cars manufactured in the United States in 40 years. Amtrak also replaced their aging F-40 locomotives with 150 nearly new locomotives.
High-speed passenger rail service continues to build momentum, albeit slowly. Box 1-1 discusses its status in the United States.
Air transportation is the fastest growing transportation mode. Domestic passenger-miles of air travel more than doubled since 1980, while ton-miles of freight carried by air increased threefold2. Airway system mileage increased from 341,000 miles in 1980 to 394,000 in 1995; no estimates are available for 1996 and 1997. In 1997, the United States had 18,345 airports of all sizes and descriptions, about 20 percent more than in 1980. The increase over the period is explained by the addition of over 3,200 general aviation airports, which totaled 17,685 in 1997. Certificated airports (those serving scheduled air carrier operations with aircraft seating more than 30 passengers), on the other hand, de-creased from 730 in 1980 to 660 in 19973. This decline probably reflects the influence of the hub-and-spoke systems used by most major airlines since airline deregulation in the late 1970s (USDOT BTS 1998, table 1-2).
Airport runway quality improved from 1986 to 1997. The percentage of public-use airports with paved runways increased slightly, as did the percentage with lighted runways (USDOT BTS 1998, table 1-2). Runway pavement quality also improved at the subset of airports listed in the Federal Aviation Administrations National Plan of Integrated Airport Systems (NPIAS). The NPIASs classification of airports includes those with commercial service, all reliever airports, and selected general aviation airports. Runways in poor to fair condition dropped from 39 percent in 1986 to 28 percent in 1997, while those in good condition rose from 61 percent to 72 percent. Airport runway conditions at commercial service airports, a subset of the NPIAS, have remained nearly static, though, with 79 percent in good condition in 1997. The remaining 21 percent of commercial airport runways were classified as poor or fair (USDOT BTS 1998, table 1-36). Still, overall commercial airport runways remain in better condition than NPIAS airports.
The number of aircraft operated by certificated air carriers increased from 7,320 in 1992 to 7,616 in 19974. (USDOT FAA 1999b). Totals for the entire certificated fleet are not available for years prior to 1992, though growth is evident for the portion of the fleet for which pre-1992 data are available.
The general aviation fleet consisted of over 192,000 active aircraft in 1997, the third consecutive year of increase. A decline in the fleet occurred between 1989 and 1994from 205,000 aircraft to 172,000 aircraft. General aviation aircraft are flown for a variety of purposes. The most popular is personal use (60 percent), followed by business (14 percent), instruction (8 percent), and corporate activities (5 percent), with smaller portions of the fleet used for air tours, sightseeing, air taxi, and other applications. Most active general aviation aircraft (52 percent of those whose ages are known) are 25 years old or less, 40 percent are between 26 and 50 years old, and 8 percent are over 50 years old (USDOT FAA 1999a; USDOT FAA 1998).
U.S. water ports handled approximately 2.3 billion tons of foreign and domestic waterborne commerce in 1997 (USACE 1997). International shipments increased by one-third between 1980 and 1997, while domestic shipmentscoastwise, inland, and on the Great Lakesincreased very little. About 27 percent of the world merchant fleet called at U.S. ports in 1997, representing 44 percent of the worlds dead-weight-tonnage capacity (USDOT BTS MARAD USCG Forth-coming).
The port and waterway system plays an important role in recreation and tourism. Of the 223 large cruise ships in the world fleet, about half (109) call regularly at U.S. ports. In addition, recreational boating is a major activity. Approximately 12.3 million recreational boats were numbered (registered) in the United States in 1997, compared with 10 million in 1987 and 8 million in 1977. Numbered recreational boats increased by 441,000 in 1997, the most growth in a single year since 1988. An unknown number of other boats are not registered (USDOT BTS MARAD USCG Forthcoming).
In the United States, 25,000 miles of commercially navigable waterways serve 41 states, including all states east of the Mississippi River (USACE 1999a). Hundreds of locks facilitate travel along these waterways. The U.S. Army Corps of Engineers owned or operated 276 lock chambers at 230 sites in 1997, with lifts ranging from 5 to 49 feet on the Mississippi River and up to 110 feet at the John Daly Lock on the Columbia River (USACE 1999b, 1999c). In January 1999, 135 of the 276 chambers had exceeded their 50-year design lives. The oldest operating locks in the United States, Kentucky River Locks 1 and 2, were built in 1839 (USACE 1999c).
U.S. ports, or marine terminals, function as intermodal freight connections between water vessels and highway and rail networks. In 1997, the nations marine terminals were nearly equally divided in number among deep-draft (ocean and Great Lake) and shallow-draft (inland waterway) facilities with 1,914 located along the coasts (including Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands) and Great Lakes and 1,812 located along inland waterways (USDOT MARAD 1998). Nearly 90 percent of inland facilities were privately owned in 1997 compared with about two-thirds of coastal facilities.
In 1997, 86 percent of the inland ports were used primarily for the transfer of bulk commodities such as grain, coal, and petroleum; only 14 percent of these ports were general cargo or multipurpose terminals. At coastal terminals, general cargo accounted for 37.5 percent of the berths (including the Great Lakes) and a similar share (41.2 percent) was used for bulk commodities. About 2.8 percent of coastal berths served -passenger vessels, 11.2 percent served barges, 4.2 percent- were used for mooring or other purposes, and 3 percent were inactive (USDOT MARAD 1998).
Over the next few years, coastal ports will be faced with the challenge of handling the next generation of containerships. Each megaship has a capacity of 4,500 20-foot equivalent container units (TEUs) or more, and drafts of 40 to 46 feet when fully loaded. The first of these vessels was delivered in 1996, and containership operators around the world may take delivery of 35 more through 1999. To physically accommodate megaships at U.S. ports, channel and berth depths must be at least 50 feet. However, only 5 of the top 15 U.S. container portsBaltimore, Tacoma, Hampton Roads, Long Beach, and Seattlehave adequate channel depths, and only those on the west coast have adequate berth depths. In addition, ports may need to expand terminal infrastructure, such as cranes, storage yards, and information systems, to facilitate the increased volumes of cargo from these ships. Also, landside modes and facilities connecting with water terminals will face higher volumes of rail and truck traffic. Many ports have initiated expansion projects to accommodate these ships. How effectively U.S. ports handle this next generation of containerships will have implications for the efficiency of the U.S. transportation system and U.S. trade competitiveness (USDOT MARAD 1998, 4951).
The U.S.-flag commercial vessel fleet in-creased to 41,419 in 1997, compared with 38,788 in 1980 (USACE NDC 1999; USACE WRSC 1998). Barges accounted for the overwhelming sharenearly 80 percent of the entire fleetboth in terms of number of vessels and cargo capacity. Tugboat and towboats accounted for around 12.5 percent of the fleet, and other self-propelled vessels such as dry cargo ships, cruise ships, tankers, and offshore support vessels accounted for the remainder.
Self-propelled vessels, such as tankers, containerships, and dry bulk carriers, have larger cargo capacity than barges (see table 1-4). Tankers have the most capacity51,000 short tons on average (the largest tankers have a capacity of over 262,000 short tons). The average carry of liquid and dry cargo barges was 1,700 short tons.
Cruise ships, gambling/casino boats, and vessels reported as employed in sightseeing, excursions, and other such activities numbered 1,206 in 1997. These vessels had an average capacity of 298 passengers. There were 5,713 tugboats/ push-boats available to operate or operating during 1997. Of these, about 32 percent had 500 to 1,000 horsepower and were, on average, 26 years old, and 17 percent were under 500 horsepower and averaged 34 years of age5.
The average commercial vessel (including cargo, passenger, and other vessels) in 1997 was about 27 years old. Containerships were, in general, newer than the rest of the fleet, averaging about 16 years, while dry bulk carriers were the oldest, averaging 28 years. Passenger vessels averaged about 21 years old. Ferries in operation in the United States averaged about 23 years old.
BTS and two other Department of Transportation agencies, the Maritime Administration and the U.S. Coast Guard, will issue a comprehensive report on water transportation in late 1999 (see box 1-2).
OIL AND GAS PIPELINES
An extensive system of pipelines is in place for transmission of petroleum, petroleum products, and natural gas throughout the country. The extent of the network and the amount of pipeline activity are unclear due to differences in national estimates and gaps in publicly available data. Table 1-1 shows Eno Foundation estimates for oil pipelines and American Gas Association estimates for natural gas pipelines.6.
In 1997, 556 federally assisted transit agencies provided service in urbanized areas of the United States. About 98,000 vehicles were available for maximum service8 in that year. Of these, over 76,000 vehicles operated in maximum service, carrying nearly 8 billion passenger trips. Federal law requires these transit agencies to report their financial and operational activities to the Federal Transit Administration (FTA). Agencies operating 9 or fewer vehiclesthere were 66 such agencies in 1997are not required to submit detailed data.9 There are other transit operations that may not be required to report data to FTA (e.g., private subscription bus services and some rural operators); these are not included in the discussion that follows.
Over three-quarters of the 76,000 transit vehicles were operated in urbanized areas with a population of 1 million or more, while only about 9 percent operated in areas with a population of less than 200,000. Fixed-route buses, demand responsive service, and heavy rail were the most prevalent transit modes. Bus accounted for 58 percent of passenger trips and 44 percent of passenger-miles. Heavy rail accounted for 30 percent of passenger trips by transit and 30 percent of passenger-miles. Buses and demand responsive vehicles are common in cities of all sizes, but fixed-rail modes are found almost exclusively in large urban areas with a population of more than 1 million.
The total number of vehicles operated in maximum service increased by a modest 12 percent between 1992 and 1997, with most of this increase due to growing numbers of demand responsive vehicles and vehicles used in vanpool service. Buses accounted for over 57 percent of reported transit vehicles operated in maximum service, and demand responsive vehicles accounted for 18 percent. Heavy-, commuter-, and light-rail vehicles accounted for 11, 6, and 1 percent of the reported fleet, respectively. Vehicles used in other modes such as vanpools, trolleys, and ferry boats accounted for approximately 7 percent of the fleet.
Federally assisted public transit agencies in urbanized areas operated and maintained over 10,800 directional route-miles of fixed guideway in 1997, compared with 8,900 in 1992a 21 percent increase in just 5 years. Included in this total is bus exclusive and access-controlled rights-of-way, which increased 60 percentfrom 790 miles to 1,266 milesduring this period (see figure 1-3).
In addition to service provided along fixed guideways maintained by transit agencies, buses provided service over 154,489 directional route-miles of public highway in 1997. Directional route-miles of bus service on mixed right-of-way public highways shows little or no real growth over this period.
Heavy-, light-, and commuter-rail services also expanded directional route mileage, increasing by 8.9, 17.0, and 20.0 percent, respectively. The increase in light rail is due, in large part, to the opening of new service in Denver (10.6 route-miles) and St. Louis (34 route-miles) in 1994 and new service in Dallas, which began in 1996 (23 route-miles) and expanded by an additional 17.8 route-miles in 1996/97. Ferryboat, trolley bus, and other transit modes also increased route mileage during this period.
There were approximately 5,000 other transit agencies in existence in 1997. About 4,000 of these were federally assisted with 1,000 serving rural areas (Section 18 operators) and 3,500 providing service to people with special needs (Section 16 operators) (APTA 1999).
The average age of transit vehicles overall was stable between 1992 and 1997, largely because buses, the most numerous vehicle type, showed little change. The average age of buses in 1997 was 8.1 years, compared with 8.3 in 1992. Demand responsive vehicles averaged 3.4 years, the same as in 1992 although the average increased to 3.7 in 1993/94. The average age of light-rail vehicles was 15.9 years in 1997, compared with 17.1 years in 1992. Commuter rail and heavy rail, on average, have the oldest vehicles, and during this period show the most increase in average age. The average age of commuter-rail vehicles rose by 2.1 years to 20.6, and heavy rail increased from 17.8 to 21.1 years.
INFORMATION TECHNOLOGY USE IN TRANSPORTATION
Railroading, aviation, and marine navigation have actively used information technologies (IT) to enhance the capabilities of the transportation system, as evidenced by the rapid diffusion of transportation applications for such innovations as the telegraph in the 19th century, and radio and radar in the first half of the 20th century. (Box 1-3 discusses innovative applications for IT in the railroad industry.) Advances in telecommunications and computer hardware and software allow all modes of transportation access to IT applications, including highways and transit, which previously used information and communications technologies less intensively than other modes.
Intelligent transportation systems (ITS), which comprise a broad range of technologies, help to improve the efficiency and effectiveness of transportation. Electronic surveillance, communications, and traffic analysis and control technologies provide information and guidance to transportation system users and help transportation agencies monitor, route, control, and disseminate information.
ITS for highway and transit is in the early stages of implementation. Particular goals include improving safety, reducing travel time, and easing delay and congestion. Tracking of deployment is complicated by the variety of technologies and approaches that could be classified as ITS. However, implementation is expanding, especially in larger urban areas troubled by traffic congestion. A federal survey of ITS in 78 of the largest cities in the United States was conducted between the summer of 1997 and the summer of 1998. Data were collected on deployment of nine components of ITS infrastructure for highways, transit, and highway-rail grade crossings within the boundaries of the metropolitan planning organizations (MPOs) for these large metropolitan areas (see figure 1-4). Several technologies or approaches could be utilized in a single component.
Global Positioning Systems (GPS) are in use in numerous transportation modes (even walking), although to what extent is uncertain. For the MPOs surveyed above, 23 percent showed some deployment of automatic vehicle location devices in fixed-route or light-rail transit vehicles. In 1996, the U.S. Coast Guard brought its Differential GPS online. Reference stations located every 200 miles along the coast and major rivers allow ships with the proper GPS receiving equipment to identify their positions within 5 to 10 meters, compared with 100 meters for other positioning systems. This is an important navigational aid, as some channels are less than 100 meters wide.
GPS is used for both commercial and general aviation. About 70 percent of corporate and over half of business-use aircraft have GPS devices, compared with about 40 percent of personal-use aircraft (USDOT FAA Forthcoming, table 7.2).
Information about the extent of the nations transportation infrastructure and vehicle fleet is fairly complete for most modes. However, publicly available data for gas and liquid pipelines differ among sources, and accurate, national-level estimates of the pipeline inventory are not available on an annual basis. Transit vehicle information from public agencies that do not report to FTA is limited, yet these agencies purchase or support sizable amounts of transit services. Few national data are available about the number of small, rural transit providers and organizations that provide transit as a secondary service (e.g., shuttle and dial-a-ride services provided by hotels, airports, universities, and others). Also, as ITS evolves and its implementation becomes more extensive, it will become important to have a comprehensive inventory of this technology across the nation.
Information about the condition of transportation vehicles and infrastructure is spotty and uncertain. Condition data for highways, bridges, and airport runways have a long history, but for other infrastructure as well as for vehicles, vessels, and aircraft, age is one of the few indicators available, and few age data exist. Also, as the quality and expected lifetime of these transportation elements often change, and because other factors affect new vehicle sales, age alone is an inadequate measure.
American Public Transit Association (APTA). 1999. Available at www.apta.com/stats/index.htm.
Association of American Railroads (AAR). 1998. Railroad Facts. Washington, DC.
National Railroad Passenger Corp. (NRPC). 1998. Amtrak Annual Report. Washington, DC.
Oak Ridge National Laboratory (ORNL). 1999. Summary of Travel Trends: 1995 Nationwide Personal Transportation Survey. Oak Ridge, TN.
Penn Well Publishing Co. 1998. Oil & Gas Journal 96:35. Tulsa, OK.
R.L. Polk Co. 1999. Personal communication.
U.S. Army Corps of Engineers (USACE). 1997. Waterborne Commerce of the United States, Calendar Year 1996; Part 5--National Summaries. New Orleans, LA: U.S. Army Engineer District.
____. 1999a. Internet website. Available at www.wrsc.usace.army.mil/ndoooc/fcdidu3.htm.
____. 1999b. 1997 Lock Characteristics Data-base. Available at www.wrsc.usace.army.mil/ndc/datalck.htm.
____. 1999c. Lock Fact Sheet. Available at www.wrsc.usace.army.mil/ndc/fcdidu3.htm.
U.S. Army Corps of Engineers (USACE), Navigation Data Center (NDC), Waterborne Commerce Statistics Center. 1999. Vessel Characteristics Data Base. New Orleans, LA.
U.S. Army Corps of Engineers (USACE), Water Resources Support Center (WRSC). 1998. Waterborne Transportation Lines of the United States, Calendar Year 1996: Volume 1--National Summaries. Fort Belvoir, VA.
U.S. Department of Transportation (USDOT), Bureau of Transportation Statistics (BTS). National Transportation Statistics 1998. Available at www.bts.gov.
U.S. Department of Transportation (USDOT), Bureau of Transportation Statistics BTS), Maritime Administration (MARAD), U.S. Coast Guard (USCG). Forthcoming. Maritime Trade & Transportation 1999. Washington, DC.
U.S. Department of Transportation (USDOT), Federal Aviation Administration (FAA). 1998. FAA Statistical Handbook of Aviation 1996. Washington, DC.
____. 1999a. General Aviation and Air Taxi Survey 1997. Washington, DC.
____. 1999b. Personal communication.
U.S. Department of Transportation (USDOT), Federal Highway Administration (FHWA). 1997. Highway Statistics Summary to 1995. Washington, DC.
____. 1998a. Highway Statistics. Washington, DC.
____. 1998b. National Bridge Inventory Database.
____. Annual editions. Highway Statistics. Washington, DC.
U.S. Department of Transportation (USDOT), Federal Transit Administration (FTA). 1999. 1997 National Transit Summaries and Trends. Washington, DC.
U.S. Department of Transportation (USDOT), Maritime Administration (MARAD). 1999. A Report to Congress on the Status of the Public Ports of the United States 19961997. Washington, DC.
3 The number of certificated airports differs from that for airports serving large certificated carriers shown in table 1-1.
5 Average capacity calculation excludes two vessels for which passenger capacity data were not available; average cargo capacity calculation excludes 52 vessels for which cargo capacity data were not available.
6 Two federal agencies estimate oil and natural gas pipeline mileage: the Federal Energy Regulatory Commission (FERC) and the Office of Pipeline Safety (OPS) in the U.S. Department of Transportations Research and Special Projects Administration. Their mileage estimates differ, largely due to jurisdictional differences. FERC collects data for pipelines involved in interstate commerce or those with continuous flow, including gathering lines. Operators with an annual revenue of less than $350,000 are excluded. OPS, on the other hand, collects data for all pipelines except gathering lines of 6 inches or less in diameter, pipelines owned by companies with fewer than 30 miles of pipe nationwide, and gas lines less than 1 mile in length. These criteria are illustrative and are not complete. Additional criteria determine whether a pipeline is under FERC and/or OPS jurisdiction.
8Vehicles operated in maximum service is defined as the number of vehicles used during the peak day, week, and season of the year, excluding atypical days and one-time special events. Vehicles available for maximum service refers to the total number of vehicles held by a transit agency, except emergency contingency vehicles and those awaiting sale.