Chapter 2
Transportation System Extent and Condition

Introduction

Luggage carousel at Ronald Reagan Washington National Airport in Washington, DC.

The U.S. transportation system makes possible a high level of personal mobility and freight activity for the nation’s 281 million residents and nearly 7 million business establishments. In 1999, over 230 million motor vehicles, transit vehicles, railroad cars, and boats were available for use on the over 4 million miles of highways, railroads, and waterways that connect all parts of the United States, the fourth largest country in the world in land area. The transportation system also includes about 213,000 aircraft and over 19,000 public and private airports (an average of about 6 per county), and over 400,000 miles of oil and gas transmission lines. This extensive transportation network supported about 4.6 trillion passenger-miles of travel in 1999 and 3.8 trillion ton-miles of commercial freight shipments in 1999.

In general, the nation’s transportation infrastructure has changed very little in recent years, while the number of vehicles has grown, in some cases dramatically. Road lane-miles, for instance, have grown by about 3 percent between 1980 and 1999, while cars and light trucks have increased by 40 percent. In air transportation, the number of aircraft operated by air carriers has increased by more than 30 percent since 1990, while the number of certificated airports (those serving scheduled air carrier operations with aircraft seating more than 30 passengers) has shrunk. The heavy use of the nation’s infrastructure raises the specter of deterioration. Data show, however, the nation’s roads, bridges, and airport runways, in general, improved in the 1990s.

As the level of traffic continues to climb and the amount of infrastructure remains the same, improved management of the system is one method being used to keep traffic flowing. The increasing use of information technology is important not only in commercial aviation, railroading, and waterborne commerce, but also in highway transportation, transit, general aviation, and boating. Information technology enhances the capability to monitor, analyze, and control infrastructure and vehicles, and offers real-time information to system users. These technologies have a great deal of potential to help people and businesses use the transportation system more efficiently.

Transportation System Extent

The widespread availability of a large variety of transportation options brings a high level of mobility to most of the nation’s residents and businesses. Table 1, table 2, table 3, table 4, table 5 and table 6 provide a snapshot of the key elements of the U.S. transportation system.

To put the system into perspective, the system’s 4 million miles of roads would circle the globe more than 157 times, its rail lines 7 times, and its oil and gas pipelines 56 times. The average distance traveled by each car and light truck annually (about 12,000 miles) equals a journey nearly halfway around the world, or added together, about one-tenth the distance to the nearest star outside our solar system.

The capacity of the air and transit systems in the United States is also phenomenal. There are more than enough seats on airplanes operated by U.S. air carriers to seat the entire population of Delaware (population 780,000). And the number of cars in the New York City subway system alone is more than large enough for the entire population of Baton Rouge, Louisiana (population about 200,000), to have a seat at the same time.

Restructuring and Consolidation of Transportation Industries

Aviation

The aviation industry has grown dramatically and changed since the Airline Deregulation Act of 1978. It has experienced consolidation, while at the same time, new-entrant, low-fare competitors have emerged. Some older, established airlines, such as Eastern, National, and Pan American, have disappeared, while others, such as Southwest Airlines, a former intrastate carrier, have become major airlines. As a result, the number of major airlines has changed relatively little since 1980, even though airlines have come and gone.

Deregulation created major opportunities for smaller airlines, known as nationals and regionals. Before deregulation, these smaller airlines tended to operate on the fringes of the service areas of the large commercial air carriers. The typical smaller airline was a fixed-base operator that provided scheduled air service to small communities using small aircraft that seated fewer than 30 passengers.

After deregulation, national and regional airlines became increasingly important sources for connecting traffic to major carriers. These connections led to the next significant trend to evolve from deregulation—the development of “code-sharing” agreements between the major and nonmajor air carriers. Code-sharing is a common industry practice in which one airline offers services in its own name for a particular city-pair, but some, or all, of the transportation is provided by another carrier. More recently, the larger air carriers began purchasing their smaller partners. The close relationship between the regional, national, and major air carriers continues to shape the industry today.

In 1999, the national and large regional carriers enplaned 84 million people, up from 51 million in 1980. The share of passengers enplaned by majors has increased over this period, however, going from 81 percent to 85 percent.

Rail

The freight railroad industry has consolidated greatly over the past 25 years. Today, there are only 8 Class I (major) railroads in the United States, down from 73 in 1975. Between 1975 and 1999, the Class I railroads increased their traffic (measured in ton-miles) by 90 percent, while their network (miles of road owned) declined by about 50 percent and the number of employees declined by about 60 percent. During this same period, Class I railroad industry labor productivity, measured by revenue ton-miles per employee, soared (figure 1). In 1975, Class I railroads owned approximately 192,000 miles of road (route-miles). By 1999, Class I companies owned about 99,000 miles of rail line. Many of the lines have been sold to new, aggressive regional and short-line railroads (Class II and III), especially since the Staggers Act of 1980 that encouraged sales to small railroads rather than abandonment. Today, these railroads operate a total of 50,000 miles of road [2].

Water

During the 1990s, the shipping industry underwent major consolidation in an effort to improve its efficiency and productivity. Some of the important mergers were P&O Container and Nedlloyd, Neptune Orient and APL Ltd., and Sealand and Maersk. Liner carriers¹ are currently using vessel-sharing arrangements with other carriers to improve productivity. As a result, individual companies have less need to provide direct services to multiple ports. Carriers can move cargo through a limited number of hub ports and use other modes, such as train, air, truck, or vessel feeder services, to connect the hub with the cargo’s ultimate destination or origin. In the United States, the ports of Long Beach and Los Angeles in California are the largest container hub ports in North America.

The U.S. Congress deregulated the shipping industry in 1988 when it passed the Ocean Shipping Reform Act (OSRA). OSRA allows shippers and ocean carriers to enter, for the first time, into confidential service contracts that must be filed only with the Federal Maritime Commission. Previously, a system of conferences (voluntary associations of ocean carriers) set rates. Under earlier Acts, the carriers had to share rate information with all other shippers, who could then demand similar rates from ocean carriers. Now rates may be negotiated on a case-by-case, one-to-one basis between shippers and carriers. OSRA strengthens provisions that prohibit unfair foreign shipping practices and provides greater protection against discriminatory actions. The Act could also lead to another round of consolidation in the industry.

Consolidation in the cruise line industry, through acquisitions and mergers, has provided the top companies with more financial strength and marketing muscle to promote their ships and control costs, contributing to the stability of the industry in the late 1990s. For instance, in 1998, the top four North American cruise lines controlled 82 percent of the North American cruise capacity, up from 61 percent in 1995. In fact, these companies controlled an even larger share of the market because their newer vessels tend to sail at higher percentages of capacitythan those of smaller lines [3].

¹ A cargo-carrying ship operated between specified ports on a regular basis for an advertised price, versus a chartered ship that operates for single deliveries to a variety of ports.

Motor Carriers

The motor carrier industry comprises truck and bus companies. In the mid-1970s, the motor carrier industry was regulated by the Interstate Commerce Commission (ICC), which controlled routes of service and rates through its rate bureaus. Startup companies were required to prove that their plan to provide new service was in the public’s best interest. Only a limited number of truck and bus companies were authorized to provide service—18,000 truck companies in 1975 compared with nearly 500,000 companies in operation today [6]. Responding to concerns about the economic inefficiency of the trucking industry, ICC loosened the entry standards in the late 1970s. The Motor Carrier Act of 1980 further eased barriers to entry. In the early 1980s, the use of private carriers (“in-house” trucking fleets) declined as companies chose to take advantage of lower rates and improved service by for-hire carriers. Of the nearly 500,000 trucking companies providing service today, most have 6 or fewer trucks (table 1). About 3,200 carriers have more than 100 trucks [5].

Bus companies, too, were given authority to set rates and determine routes as a result of deregulation in 1982. Economic deregulation spurred strategic reorganization of the bus industry, creating conditions for improved services. In certain cases, however, deregulation resulted in diminished services.

Greyhound and Trailways merged in 1987 to provide a larger network of intercity bus service. This strategic agreement resulted in improved intercity service and better scheduling and fare information. In addition, new, smaller regional carriers have started providing service to specialized niche markets. These carriers not only serve geographic markets, but also sectors of the population, such as senior citizens, metropolitan commuters, vacation travelers, or luxury travelers. About 4,000 private motorcoach companies now operate in the United States and Canada, offering charters, tours, regular route service, and other bus services [1].

Following deregulation and with increasing competition from airlines and automobiles, bus companies eliminated many unprofitable routes and stops, particularly in rural areas. In 1982, more than 11,000 locations were served nationwide, down from 16,000 in the early 1970s [4]. Today, the number of locations served has fallen to just about 5,000, with much of the curtailed service in rural areas. The Transportation Equity Act for the 21st Century provides support for the intercity bus needs of rural residents.

Sources
1. American Bus Association, Industry Profile: Motorcoach Industry Facts, available at http://www.buses.org, as of July 26, 2000.
2. Association of American Railroads, Railroad Facts (Washington, DC: 2000).
3. Mathiesen, Oivind (ed.), Cruise Industry News 1998 Annual (New York, NY: Cruise Industry News, 1998).
4. U.S. General Accounting Office, Surface Transportation: Availability of Intercity Bus Service Continues To Decline, GAO/RECD-92-126 (Washington, DC: 1992).
5. U.S. Department of Transportation, Federal Motor Carrier Safety Administration, Motor Carrier Management System Report LS50B901 (Washington, DC: March 2000).
6. ____. personal communication, Aug. 1, 2000.

Information Technology Use

From the telegraph used by railroads in the 19th century to radio and radar used in ships and planes at the beginning of the 20th century, information technology (IT) has enhanced the capabilities of our transportation systems. In recent years, these technologies have been integrated into all modes of transportation. Highway and transit applications of IT now are joining the other modes as new technology allows drivers to “navigate” roads.

Intelligent transportation systems (ITS) comprise a broad range of technologies, including those in the IT category, and help improve the efficiency, effectiveness, and safety of transportation. Travelers can obtain information and guidance from electronic surveillance, communications channels, and traffic analysis. ITS also boosts the capability to monitor, route, control, and manage information to facilitate travel.

The variety of technologies and approaches across the ITS spectrum, however, complicates the tracking of deployment. The U.S. Department of Transportation, Federal Highway Administration’s ITS Joint Program Office conducted two surveys, in 1997 and 1999, to gauge urban implementation in 75 metropolitan areas in the United States [2]. The surveys collected data on deployment for nine ITS infrastructure components for highways, transit, and highway-rail grade crossings within the boundaries of metropolitan planning organizations (MPOs).

A single ITS component may utilize several technologies or approaches. For instance, electronic toll collection (ETC) technologies automatically collect payments through the application of in-vehicle, roadside, and communications technologies. Over 43 percent of the metropolitan areas surveyed had toll collection lanes with ETC capacity, up from 36 percent in 1997 [2].

Multiple ETC technology deployment highlights the growing importance of integrating ITS.Beyond measuring fixed ITS assets like vehicles, the ITS Joint Program Office also studies the integration among agencies operating the infrastructure. Federal officials define ITS integration as the transfer of information between three types of organizations: state departments of transportation, local governments, and transit agencies.

Traffic signal control and electronic toll collection are two of the top three highway ITS technologies currently being deployed (figure 1). These technologies directly benefit travelers by smoothing out trips on toll roads and signaled arterial roads. Highway-rail grade crossings have one of the lowest rates of deployment penetration, but a major federal initiative is providing funds to address this area (see the section on high-speed rail corridors elsewhere in this chapter).

The Global Positioning System (GPS) is being used in all transportation modes (even walking), although to what overall extent is uncertain. Thirty percent of the surveyed metropolitan areas showed some deployment of automatic vehicle location devices in fixed-route transit vehicles [2]. GPS is not only used for commercial aviation, but it is also used for 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 [1]. In 1996, the U.S. Coast Guard brought its Maritime Differential GPS (DGPS) 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. The U.S. Department of Transportation is now implementing Nationwide DGPS to bring the same positioning accuracy to all parts of the continental United States and Alaska.

Railroads are developing positive train control (PTC) systems that will use nationwide DGPS to provide precise positioning information. PTC can prevent overspeed accidents and collisions between trains and between trains and maintenance-of-way crews. PTC can also improve the efficiency of railroad operations by reducing train over-the-road delays and increasing running time reliability, track capacity, and asset utilization. [3].

Sources
1.U.S. Department of Transportation, Federal Aviation Administration, General Aviation and Air Taxi Survey, 1996, available at http://api.hq.faa.gov/ga96/gatoc.htm, as of Dec. 5, 2000, table 7.2.
2. U.S. Department of Transportation, Federal Highway Administration, ITS Joint Program Office, Tracking the Deployment of the Integrated Metropolitan Transportation Systems Infrastructure in the USA: FY 1999 Results, May 2000, available at http://www.itsdocs.fhwa.dot.gov, as of Feb. 8, 2001.
3. _____. “What Is Positive Train Control?” available at http://www.volpe.dot.gov, as of Dec. 4, 2000.

Roads

Road building and widening continue to slowly increase the extent of the public road system and the length of lane-miles open to the public. Since 1980, miles of public road increased only about 1.5 percent, although lane-miles increased twice as much (3.2 percent). Paved roadways constituted about 62 percent of all highway mileage in 1999, up from 54 percent in 1980 and 24 percent in 1950. Nearly all of the public roads in urban areas are paved. However, about half of the miles of rural public roads are unpaved, accounting for 97 percent of total unpaved public road miles—much the same ratio as in 1980 (figure 1) [1].

Source
1. U.S. Department of Transportation, Federal Highway Administration, Highway Statistics (Washington, DC: Annual editions).

U.S. Vehicle Fleet

Between 1989 and 1999, the most noteworthy development in the U.S. vehicle fleet was the rapid growth in the number of registered light-duty trucks, including minivans, pickups, and sport utility vehicles (figure 1). During this period, the number of these vehicles grew from nearly 46 million to over 75 million, an increase of about 64 percent. This category now accounts for 34 percent of the total U.S. fleet, up from 23 percent in 1989. Fueled by the rapid increase in the number of light-duty trucks, the total U.S. fleet grew to nearly 220 million vehicles in 1999, an 11 percent increase over the 198 million vehicles registered in 1989 [1].

In contrast to the rapid growth of light-duty trucks, the number of other types of vehiclesremained relatively steady, while the shares declined in some cases. The number of cars, though still 60 percent of the total fleet at nearly 132 million vehicles in 1999, decreased slightly over the past 10 years, and accounted for nearly 10 percent less of the total fleet in 1999 than in 1989. Over the same period, the number of large trucks and buses increased at roughly the same rate as the total U.S. fleet, while motorcycle registrations declined somewhat [1].

Source
1. U.S. Department of Transportation, Federal Highway Administration, Highway Statistics 1999 (Washington, DC: 2001).

High-Speed Rail Corridors

In recent years, high-speed rail (HSR) service for intercity passengers has experienced renewed interest). HSR technologies allow trains to travel at top speeds of 90 to 300 miles per hour (the highest speeds can be achieved by trains powered by magnetic levitation). Several parts of the country have HSR plans, and a number of rail corridors are under development.

In May 2000, the U.S. Department of Transportation announced grants totaling $5.3 million to five HSR corridors to eliminate hazards at public and private highway-rail grade crossings [1]. Funds can be used to close crossings, install advanced train control or traffic control systems, and upgrade warning devices, among other things. The five initially designated corridors were the Pacific Northwest Corridor, the Chicago Hub Corridor, the Gulf Coast Corridor, Southeast Corridor, and the Empire Corridor. In October 2000, the program was extended (see map).

Sources
1. Slater, Rodney, Secretary of Transportation, U.S. Department of Transportation, “Funding for Grade Crossing Hazard Elimination Programs in Designated High-Speed Rail Corridors,” May 12, 2000.
2. _____. “U.S. Transportation Secretary Slater Designates Two New High-Speed Rail Corridors, press release, Oct. 11, 2000, available at http://www.dot.gov/affairs/fra2000.htm, as of June 2001.

Urban Transit

Urban transit is a complex mix of heavy, light, and commuter rail; buses and demand responsive vehicles; ferries; and other less prevalent types such as inclined planes, trolley buses, and automated guideways. The capacity of this mode, measured by revenue vehicle-miles of service provided, grew by nearly 30 percent between 1991 and 1999 to over 3 billion miles. The U.S. population grew by 8 percent over this same period. The largest transit modes, bus and heavy rail, showed the slowest growth during this period (about 10 percent), while demand responsive transit grew the fastest (125 percent) (figure 1). Among rail modes, both light rail and commuter rail have seen substantial increases in service provided over this period, 77 percent and 23 percent, respectively [1].

The number of urban transit vehicles in rush hour service increased 26 percent between 1991 and 1999, with the number of buses rising 10 percent from 42,900 to 47,100, and rail vehicles moving up 8 percent from 12,900 to 13,900. The largest percentage gain occurred for commuter rail vehicles—17 percent, compared with 3 percent for heavy rail and 12 percent for light rail. Vehicles used in demand-responsive service soared nearly 90 percent from 8,400 in 1991 to 15,900 in 1999 [2].

The Federal Transit Administration assesses the condition of transit vehicles using a rating scale from 5.0 to 0.0 (excellent to poor condition).¹ Between 1987 and 1997, the average condition of most types of buses remained about the same, although the condition of vans improved (table 1). Most transit rail vehicles were in better condition than buses, but heavy railcars and powered commuter railcars showed notable deterioration over this period [1].

¹ These ratings come from the Transit Economic Requirements Model, which uses nonlinear deterioration curves developed from transit asset condition and replacement records.

Sources
1. U.S. Department of Transportation, Federal Highway Administration and Federal Transit Administration, 1999 Status of the Nation’s Surface Transportation System: Condition and Performance (Washington, DC: 2000).
2. U.S. Department of Transportation, Federal Transit Administration, National Transit Database, various years.

U.S.-Flag Vessels

More than 41,000 U.S.-flag vessels were available for service in U.S. maritime trade as of December 1999 [1], and 80 percent were in use that year. The segments of the U.S.-flag fleet with the highest percentage of operating vessels were dry bulk vessels, dry cargo barges, and tank barges (table 1). Barges operate primarily on the U.S. inland waterways and carry more than 90 percent of that tonnage [2]. Tankers, on the other hand, provide service primarily on the U.S. coastal waterways (table 2).

Vessel owners have been reflagging their ships to foreign registries in order to reduce operating costs (e.g., higher wages of U.S. crews). In addition, major U.S. vessel owners and operators have, in recent years, merged with or were acquired by foreign companies.

About 42 percent of the U.S. fleet is more than 20 years old (table 3). Over the next few years, many vessels in all segments will need to be replaced or rebuilt, potentially increasing activity for U.S. shipyards. In addition, approximately one-third of the self-propelled U.S. domestic fleet is more than 25 years old. While the high cost of building in U.S. shipyards may limit replacement in some segments, there are encouraging prospects in others, such as the increasing use of articulated tug/barge units as an alternative to tankers.

Sources
1. U.S. Army Corps of Engineers, Navigation Data Center, “The U.S. Waterway System—Transportation Facts,” December 1999.
2. U.S. Department of Transportation, Bureau of Transportation Statistics, Maritime Administration, and U.S. Coast Guard, Maritime Trade and Transportation 99, BTS99-02 (Washington, DC: 1999).

Ports and Cargo-Handling Services

In 1999, world waterborne trade reached 5.23 billion metric tons, the 14th year of consecutive growth [2], spurring global competitiveness among ports worldwide. U.S. ports that engage in foreign trade, and their strategic global partners, evaluate port operations in order to improve productivity. Landside congestion, intermodal connectors, water depth, and direction and concentration of trade can affect productivity.

Landside access to water ports comprises a system of intermodal rail and truck services [5]. Landside congestion, caused by inadequate control of truck traffic into and out of port terminals combined with the lack of adequate on-dock or near-dock rail access, affects the productivity of U.S. ports and the flow of U.S. international trade. Generally, productivity is difficult to measure. Cargo throughput can be used to measure physical productivity, however, it does not take into account the more efficient use of resources gained from capital investment [1].

The U.S. port industry has invested approximately $21 billion since 1946 on improvements in its facilities and infrastructure—about one-third of that total (approximately $6.6 billion) was invested between 1995 and 1999. Types of investment include new construction and modernization/rehabilitation. In 1999, new construction accounted for two-thirds of the total expenditures. Since 1994, the U.S. Pacific regions accounted for more than 50 percent of the annual investments and the majority of this investment was in the South Pacific region [4]. In the 1970s and 1980s, the North Atlantic region ranked highest in the level of total industry investments.

Changes in vessel design impact access to both landside and waterside services. For example, container vessels have increased in size and capacity, which, in turn, drives a need for adequate transshipment hub and feeder ports. Hub ports must have large capacity cranes, deep water, a large amount of backup land, and direct intermodal connections. The top ports in U.S. foreign trade are deep draft (with drafts of at least 40 feet) [3]. The majority of containerships with capacities greater than 5,000 20-foot equivalent units (TEUs) call at ports in the U.S. Pacific region (table 1).

Imports exceed exports in maritime foreign trade, particularly in the container trade. Containers entering the United States are full, but the amount of exported cargo is not enough to fill the containers for a return trip. As a result, empty containers are stacked at port terminals or intermodal transfer facilities in increasing numbers. Moreover, U.S. container trade is increasingly concentrated (see pages 121 to 122for more discussion of container trade). Today, Long Beach and Los Angeles are the top U.S. container ports. The concentration of port activity in the U.S. container trade has increased since 1998, so that the top 10 ports in the trade handle more than 80 percent of total TEUs (table 2).

Sources
1. Robinson, Dolly, Measures of Port Productivity and Container Terminal Design, Cargo Systems, April 1999.
2. United Nations Conference on Trade and Development, Review of Maritime Transport 2000, Report by the UNCTAD Secretariat (New York, NY: United Nations, 2000).
3. U.S. Department of Transportation, The Maritime Transportation System: A Report to Congress (Washington, DC: 1999).
4. U.S. Department of Transportation, Office of Intermodalism, The Impacts of Changes in Ship Design on Transportation Infrastructure and Operations (Washington, DC: February 1998).
5. U.S. Department of Transportation, Maritime Administration, U.S. Port Development Expenditure Report (Washington, DC: December 2000).

Airport Runways

In general, U.S. airport runway pavement is in good condition. When it is deteriorated, runway pavement can cause damage to aircraft turbines, propellers, and landing gear, and may result in runway closure. To prevent major problems, runway pavement requires regular maintenance to seal cracks and repair damage as well as a major overhaul every 15 to 20 years [1]. The U.S. Department of Transportation, Federal Aviation Administration (FAA), inspects runways at public-use airports and classifies runway condition as good (all cracks and joints sealed), fair (mild surface cracking, unsealed joints, and slab edge spalling), or poor (large open cracks, surface and edge spalling, vegetation growing through cracks and joints).

Airport runway quality improved from 1986 to 1999 (table 1). At the over 3,000 airports listed in the FAA’s National Plan of Integrated Airport Systems (NPIAS), runways in fair or poor condition dropped from 39 percent in 1986 to 28 percent in 1999. Those in good condition rose from 61 percent to 72 percent. At commercial service airports, a subset of the NPIAS, only 2 percent of runways were in poor condition in 1999, but the percentage in poor or fair condition—22 percent—has remained the same since 1986. Overall, however, commercial airport runways remain in better condition than other NPIAS airports.

Source
1. U.S. Department of Transportation, Federal Aviation Administration, National Plan of Integrated Airport Systems (1998-2002) (Washington, DC: 1999).

Highway Conditions

Overall, in 1999, 44 percent of the nation's roads were classified as being in good or very good condition and 17 percent as mediocre or poor; the rest were classified as fair (table 1). The generally poorer condition of urban roads, as compared with rural roads, can be attributed to the higher levels of traffic they carry. Since 1993, the condition of all roadways shows only modest improvement with rural areas outpacing urban areas [1].

In 1999, about 30 percent of urban Interstates were in poor or mediocre condition, as measured using Interstate standards (which are higher than standards for other types of roads). By contrast, only 16 percent of rural Interstate miles were classified as poor or mediocre. Despite continued growth in vehicle travel, some improvement can be seen in the condition of urban Interstates since 1993, when more than 40 percent were classified as poor or mediocre (figure 1).

Source
1. U.S. Department of Transportation, Federal Highway Administration, Highway Statistics (Washington, DC: Annual issues).

Bridge Conditions

The condition of bridges nationwide has improved markedly since 1990. Of the nearly 600,000 roadway bridges in 1999, about 29 percent were found to be structurally deficient or functionally obsolete, compared with 42 percent in 1990. About 15 percent of all bridges were structurally deficient and 14 percent functionally obsolete in 1999 [1]. Structurally deficient bridges are those that are restricted to light vehicles, require immediate rehabilitation to remain open, or are closed. Functionally obsolete bridges are those with deck geometry (e.g., lane width), load carrying capacity, clearance, or approach roadway alignment that no longer meet the criteria for the system of which the bridge is a part. Overall in the 1990s, there was a greater reduction in the number and share of structurally deficient bridges than those deemed to be functionally obsolete (figure 1).

Overall, bridges in rural areas suffer more from structural deficiencies than functional obsolescence, whereas the reverse is true in urban areas (see map and table 1). Nearly one-quarter of bridges in rural areas that support local roads were structurally deficient and one-fifth of urban Interstate bridges were functionally obsolete in 1999. Nevertheless, a large number of both structurally deficient and functionally obsolete bridges support local roads in rural areas [1].

Source
1. U.S. Department of Transportation, Federal Highway Administration, Office of Engineering, Bridge Division, National Bridge Inventory database, available at http://www.fhwa.dot.gov/bridge/britab.htm, as of Oct. 27, 2000.