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15 Longevity of Infrastructure GREGG MARLAND AND ALVIN M. WEINBERG The infrastructure of our society is largely determined by the set of capital-intensive and generally long-lived structures and devices that allow us to get what we want, get rid of what we do not want, communicate with each other, and hold the fabric of society together. This set includes the structures and devices that mediate the production and flow of the primary elements of the economy (energy, food, water, waste, materials, and finished goods) and those primarily involved in socialization (edu- cation, religion, communication, corrections, and governance). Focusing on the structures and devices of the first type, we are concerned with power plants, transmission facilities, dams, roads, bridges, and the major civil engineering works of man. Our interest here is with the longevity of these structures their mor- tality. Infrastructure is capital intensive; yet items of infrastructure may last much longer than the time required to pay for them. If these structures approach immortality, then they exist as part of the inheritance of each generation, and each generation needs only to maintain its inheritance and to add infrastructure capital as the systems grow. If, on the other hand, the major capital items of infrastructure are relatively short lived, then each generation has both a greater obligation to supply its own infra- structure capital and a greater opportunity to affect the character of its own infrastructure. This chapter poses three ostensibly similar questions about the longevity of infrastructure: How long does it last? How long could it last? How long 312
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LONGEVITY OF INFRASTRUCTURE 313 should it last? These questions are in fact distinctly different and are by nature historical, technical, and ethical, respectively. THE IMMORTALITY OF INFRASTRUCTURE These questions all raise an initial question about when and why struc- tures are judged to be no longer serviceable. Why are structures replaced, and what determines their lifetime? The following considerations are lim- iting: · Devices wear out. · Operation and maintenance become too expensive- often because parts become difficult to replace or because operations are too labor in- tensive and labor costs escalate. · Competing systems and technologies become available arid are cheaper, less polluting, more attractive aesthetically, or of a scale (usually larger) better suited to achieving the system's purpose. The following section presents a brief, anecdotal view of the history and longevity of several types of structures (power plants, dams, bridges, and roads) and then returns to ruminate over the last two questions: How long could they last, and how long should they last? Electric Power Plants Analysis of the longevity of energy-producing devices raises a moral issue: what responsibility do those who build polluting and possibly dangerous electric power plants owe to future generations? It could be argued that, insofar as these devices are inexpensive to operate, the generation that paid for their construction was compensating later gen- erations for any such burden with the gift of relatively cheap electric- ity provided the later generation does not have to rebuild the power- producing devices. Ire an article in Energy Policy, this argument was presented, based on an analysis of the costs and longevity of systems for producing inex- haustible power from dams, fission and fusion reactors, and solar devices. The burden of the argument was as follows: If plants last very much longer than their design life, and if their maintenance costs do not grow excessively, then the product of such plants will eventually become remarkably cheap. If the plants produce electricity from one of the inex- haustibles-solar, fission breeders, or fusion then the cost of electricity can be expected to become very low, perhaps around 1¢/kWh.... Ordinary economics discounts the future at a rate that reflects our uncertainty
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.314 GREGG MARLAI\D AND ALVIN M. WEINBERG 25 _ 20 `~\ o - 10 be 15 5 "Gil - an< MW /' 4 ~\ \ 1 - 5 10 15 20 25 Age of Units (years) 500 400 300 100 30 35 40 - - o ID 200 N O$ FIGURE 15-1 Age of the total U.S. thermal electricity generating capacity (coal, oil, gas, nuclear). SOURCE: Electrical World (1985~. Reprinted with permission. about the future, as well as the realities of today's money markets. Should we discover that these gadgets last "forever," economic doctrine would still forbid our investing in them rather than in more immediate gadgets whose lifetime, and pay-off, is much shorter. Large "immortal" energy systems might acquire much the same status as roads and bridges part of society's infrastructure, for which society is prepared to pay more than strict economic accounting would dictate. Thus a political decision, one dictated by the broad concern for the future, may be the only way to switch to the low cost "immortal" energy system. (Weinberg, 1985, pp. 58-59) Electricity from long-lived plants will be cheap only if fuel costs in these plants are low. This is the case for solar-based devices-solar cells, dams, wind turbines for which the primary energy, sunlight, is "free." To a lesser extent this is true also for nuclear energy sources fusion and breeder reactors for which the fuel cycle costs are expected to be low and practically independent of the supply of uranium. Even nonbreeder reactors have fuel cycle costs that are below the fuel cost of fossil plants. The actual lifetime of these low-fuel-cost devices can hardly be based on experience since nuclear reactors, fusion reactors, and solar plants are either nonexistent or have yet to reach the scheduled end of their lives. The oldest large power-producing reactors, located at Calder Hall in the United Kingdom, are still in operation. Although these graphite reactors are 30 years old, their operating licenses recently have been renewed. Figure 15-1 and Table 15-1 summarize the age distribution of large electrical generating plants in the United States. As of 1982 about 73 percent of all electrical capacity was in plants that were less than 20 years old; only 9 percent was in plants more than 30 years old. Some 24 percent
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316 GREGG MARLAND AI\D ALVIN M. WEINBERG of this older capacity was hydroelectric, whereas only 10 percent of the total capacity (and even less of the total generated energy) was hydro- electric. Modern electrical generating plants have usually been designed to last 30 to 40 years. This lifetime was determined not so much because the power plant wore out after that time as because the efficiency of newer power plants exceeded the efficiency of the older ones. The newer plants therefore used less fossil fuel per kilowatt-hour (kWh) and thus were cheaper to operate than the older plants. Two developments have changed our outlook on how long a power plant should be able to operate. First, fuel cost in a nuclear power plant is less important than in a fossil fuel plant; improvements in efficiency are therefore less telling in the nuclear case than in the fossil case, es- pecially if the improved efficiency requires higher capital cost. Second, the thermodynamic efficiencies of fossil power plants have tended to plateau at about 35 percent; reaching higher levels places heavy demands on the materials of construction. Thus, the original incentive to retire an old fossil plant lower thermodynamic efficiency than its newer replace- ment is no longer compelling. The electric utility industry and its suppliers have devoted much atten- tion recently to the extension of the life of existing power plants, both fossil and nuclear. In a full-page advertisement in the February 5, 1986, WallStreetJournalentitled "Life Begins at 30," the General Electric Company announced a new service dedicated to the renovation of old power plants. The economics appear to favor renovation over new con- struction by a wide margin. General Electric claims that to renovate a fossil plant costs an average of only $250/kW; on the other hand, to construct a new plant might cost almost 10 times as much. Our impression is that few completely new full-scale power plants will be built in the United States during the next 20 years or so. Instead, old fossil and nuclear plants will be renovated, thus avoiding the building of many megawatts of new central station capacity. A related issue is the siting of new fossil or nuclear power plants. In the United States there are now more than 50 nuclear power plant sites and more than 400 fossil plant sites with capacities of 400 megawatts (MOO) or more. Given the difficulty of finding new sites that are acceptable to the public, we would expect these sites, if not the devices and structures on them, to be used for a very long time. This is particularly true of the nuclear sites; yet because it is doubtful that any new nuclear plants will be built during the next 20 years, the issue may not be put to a test before the turn of the century. The geography of our electricity producing system has largely been set by the location of the existing sites.
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LONGEVITY OF INFRASTRUCTURE 317 Burwell and Lane (1980) pointed out that the existing nuclear sites, on which' are located plants capable of producing about 110 gigawatts (GW) of nuclear power, could eventually accommodate at least 340 GW of nuclear capacity. Such multiple-reactor sites are the rule outside the United States. Thus, France's 66 reactors occupy 21 sites, or about 3 reactors per site, whereas in the United States, 129 operating and planned reactors will occupy 76 sites, or 1.7 reactors per site. Although the evidence is less clear for fossil power plants, it seems likely that new, large fossil power generators will be added to existing sites rather than being built on new sites. Dams The longevity of dams has been highly variable. Many dams have lived long, useful lives, but other dams have led quite short lives and suffered dramatic terminations. Many dams have experienced drastic repairs, re- buildings, and replacements. By and large, however, dam building has progressed tremendously, and major advances have often been triggered by major failures. Changes in size and structure of dams reflect im- provements in theory, materials, construction methods and equipment, and computational capability. It is striking that dams have also seen dra- matic changes in function. The earliest dams were built for irrigation; dam building for water supply, flood control, transportation, and water power followed in sequence. By the 1 89Os the generation of electricity had begun to attain worldwide importance, and dams were used to produce hydro- electric power. Today's multipurpose dams also include soil conservation and recreation among their purposes. Although the oldest known earth dam was built nearly 5,000 years ago, real understanding of earth dam theory was not complete until around 1940 (Smith, 1972~. Before about 1870, dam building was largely an empirical process, and the failures were numerous. The useful life of a dam varies widely. The Teton Dam in Idaho was a 91-meter (m)-high modern structure completed in 1975. It failed during the initial filling. By contrast, two irrigation dams built in the second and third centuries A.D. at Merida in western Spain are still in service (Smith, 19721. Both dams at Merida are nearly 20 m high and have had a series of repairs over the centuries. The 2-kilometer (km)-long dam of the Lake of Homs, Syria, was built by the Romans about 284 A.D. and kept in use nearly 1,700 years. A bigger dam was built on top of it in 1934. Of eight dams built to supply water to Constantinople around the sixth century A.D., four are still in operation. Norman Smith observed in his book, A History of Dams, "While there is nothing to suggest that any of them
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318 GREGG MARLAND AND ALVII!,r M. WEINBERG survived in the original form, there is no doubt that some of the ancient dams still standing on the Kur (Persia) are Archaemenian in origin" (Smith, 1972, p. 56), and they date to the fifth and sixth centuries B.C. Kebar Dam (Persia) was built by the Mongols around 1300 and is still intact at 26 m height despite being badly silted. Tenth-century Moslem dams still meet irrigation needs around Valencia, Spain. The Alicante Dam on Rio Monegre in Spain was completed in 1594 and, at 41 m, stood as the world's tallest dam for almost 300 years. These dams highlight the trial-and-error successes; a rational approach to dam building did not appear until the middle of the nineteenth century. Along with the successes were many failures, the consequences of which have increased with the size of the dams. The first serious dam disaster of modern times was in 1802 when the Puentes Dam in Spain failed and cost 608 lives. A new structure was erected at the same site. Among the oldest dams still in use in the United States is the 4.5-m Espada Dam built on the San Antonio River in the mid-eighteenth century. During this same era, many small dams served and were eliminated, either purposely or through neglect. The Jones Falls Dam in New York was the highest (19 m) in North America when completed in 1832, and it remains in sound condition today (Smith, 19721. Many early dams established sites that were either rebuilt or enlarged but that remained as dam sites. The Ponte Alto Dam in Italy was 4.9 m high when first completed in 1613. With periodic heightening, it had reached 37.8 m by 1883 when another dam was built a short distance downstream to support the lowest 25.3 m of the upstream dam. A dam at Whinhill in England was completed in 1746, failed in 1815, was rebuilt in 1821, and failed again in 1835. Rebuilt a second time, it is still func . . tlonlng. "The first half of the nineteenth century was essentially a period when dams were built in markedly increased numbers but with little improvement in design and still no proper understanding of their structural behavior" (Smith, 1972, p. 1911. The first seriously designed dam was the Furens Dam, completed in 1866, at Saint-Etienne, France. At about this same time, two major dam failures focused attention on dam design, theory, and engineering. The 35.7-m-tall Habra Dam in Algeria was completed in 1870 but failed completely in 1881 when water rose 4 m above the intended maximum; in 1895 the 14-year-old, 15-m- high Bouzey Dam in France failed with a loss of 150 lives. The failure of what were thought to have been rationally designed dams led ultimately to a significantly improved understanding of dam principles. The first all-concrete dam, the 52-m San Mateo Dam near San Fran- cisco, was completed in 1889. With improvements in the design and
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LONGEVITY OF INFRASTRUCTURE 319 construction of dams, the 1920s were the last decade with an appreciable number of dam failures. By the 1930s, major modern dams were being built, but improvements in all aspects have continued to the present. For example, rock mechanics is an area of recent advances in knowledge. Improvements in engineering have brought significant increases in effi- ciency and reliability in existing hydroelectric plants. There have been two major U.S. dam failures in the last 20 years. In addition to the 1975 Teton Dam failure, the Walter Bouldin Dam in Alabama experienced a 90-m-wide breach in 1975 (the 50-m-high earthfill dam had been completed in 19571. Although the failure caused no loss of life, there was extensive flooding, and the 225-MW powerhouse was destroyed. The dam was reconstructed. Major modern dams can have extensive service periods, although they require much more maintenance than did the simpler structures of previous centuries. The Hoover Dam and the Bonneville Dam celebrated their fiftieth anniversaries in 1986 and 1987, respectively. The Grand Coulee Dam remains the marvel it was when completed in 1942. A current list of U.S. electrical generating plants contains at least six small dams that were first put into service before the turn of the century One consequence of the increasing number of dams is the exhaustion of the best sites. Improved understanding of basic principles now permits the construction of safe dams in less attractive sites. An interesting question is whether- and how major dams or dam sites might be abandoned. History offers many examples of dams rebuilt on a given site and a few examples of sites abandoned after failures. With larger dams and more intensive land use, the abandonment of good sites seems more unlikely. Smith (1972) describes several specific instances in which dams that were in- adequate by current standards were essentially replaced by being drowned by new impoundments built downstream from the existing structures. A Tennessee Valley Authority (TVA) dam, the Great Falls Dam on Caney Fork River in Tennessee, was recently considered for retirement. This is a 28-m dam with a 31,860-kW generating capacity and an 8.5- km2 reservoir with 193 km of shoreline. The primary use of the reservoir is for recreation. The dam was completed in 1916, received major mod- ifications in 1925, and was acquired by TVA in 1939. A 1983 TVA evaluation noted four significant deficiencies: dam instability, insufficient spillway capacity, leakage (which totals as much as 5.5-m3/second under and around the dam'; and deterioration and inadequacy of the power generation facilities.The TVA evaluation said in part, "based on current design criteria, the dam is not safe against overturning or sliding" (TVA, Hydropower Planning Section, 1983, p. 121. Dam removal was rejected as an option because of silt release and public disapproval (especially
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320 GREGG MARLAND AND ALVIN M. WEINBERG reservoir property owners) and because the dam area was considered a prime hydroelectric site. Another possibility that was considered (and rejected) was to run the dam to failure because the risks associated with failure were judged to be small. A major dam that was abandoned by TVA was at Hales Bar on the main stream of the Tennessee River. The Hales Bar Dam, which was begun in 1905, completed in 1913, and acquired by TVA in 1939, had an extremely poor foundation. Serious leakage was first noted 11 days after the last concrete was poured, and efforts to control the leakage continued until the decision was made to abandon the dam 50 years later. The dam was abandoned by constructing another major dam (Nickajack) 10.3 km downstream, which brought the reservoir to the initial pool level, and then dismantling the top of the older structure to avoid a hazard to navigation (TVA, Division of Water Control Planning, 1963; TVA, Office of Engineering, 19631. Siltation, another major reason dams lose their usefulness, has brought TVA to abandon powerhouses and sell dams to communities for nominal fees. A case in point was the Davy Crockett Dam in Tennessee: the dam, which was 90 percent silted up, was converted into a wildlife refuge. Lake Meade, Arizona, is estimated to have lost 3 percent of its storage capacity in 14 years and Lake Mangla in northeastern Pakistan more than 11 percent in 20 years as a result of siltation (Smith, 1972~. Although such problems as siltation may shorten the useful life of a dam, TVA engineers seem to believe that at modern dams, such as Norris on the Clinch River in Tennessee, the concrete will last forever. Bridges How long does a bridge last? There seems to be no consensus on the answer to this question. George Latimer, mayor of St. Paul, Minnesota, is reported to have said in August 1984, "Just two weeks ago our 95- year-old historic link across the Mississippi River, the High Bridge, was prematurely closed because it had rusted beyond safety standards" (Na- tional Research Council, 1985, p. 271. Henry J. Hopkins, in his book A Span of Bridges, writes, "It is rare for any metal bridge in western civilization to last more than 150 years" (1970, p. 175), and "by modern standards anyone who built a bridge that lasted 100 years would be judged a complete master" (p. 191. Yet noting that a few Roman arch bridges are still functioning, Hopkins observes, "The magnitude of the Roman achievement can only be assessed by bearing in mind that, statistically
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LONGEVITY OF INFRASTRUCTURE 321 speaking, it is virtually impossible for a bridge to last 2,OOO years" (p. 20). And J. W. Gregory agreed: "The survival of any Roman bridge is very improbable, as a modern masonry bridge, unless carefully main- tained, is estimated to last for only 70-100 years" (Gregory, 1931, p. 711. At the same time, many bridges have had lifetimes measured in days, and some have even failed to survive the removal of the construction supports. The useful lives of bridges have been ended by flood, fire, wind, rust, rot, foundation scour, war, collision, weathering, inadequacies of width or carrying capacity, and changing concepts of aesthetics. Long- lasting bridges are those that have had good form, materials, construction, abutments, and maintenance- and no military damage. Throughout his- tory, sociopolitical factors have militated against the preservation of bridges, one important reason being that efficient maintenance requires a stable central authority. The earliest specimen of a Roman arch still intact in Rome is over a drain in front of the temple of Saturn, built between the sixth and fourth centuries B.C. Other Roman bridges are more than 2,000 years old. The Ponte d'Augusto at Narni, north of Rome, was built around 220 B.C. It had four arches, one with a span of 32.3 m, and stood 33.5 m high and 8.2 m wide. Its gradual disintegration was initiated by war damage, but one arch still survives. In other places an important site has been occupied by a succession of bridges. The first record of a bridge at the site of the London Bndge was in 963, and it referred to a timber bridge. The bridge was reconstructed at least twice before a stone bridge was begun in 1176. As in other civil engineering works, bridge building has progressed through a sequence of building materials and construction methods with a large empirical foundation and gradually emerging science. "In the construction of early bridges, principles of scientific design were un- known. A bridge was built and if it failed the next one was built of heavier material" (Christensen, 1973, p. 1131. The eighteenth-century civil en- gineer Jean Perronet, a pioneer of modern bridge building, employed good science to build many French bridges and during the 1700s mastered the masonry bridge. His Pont de la Concorde was completed in 1791 and still serves Paris. The stone arch has been the world's main bridge type for 2,000 years, and many early nineteenth-century stone arches remain in use in the United States. Materials and methods have limited bridge dimensions; early arch bridges had semicircular arches and hence relatively short spans. By the nineteenth century, spans reached nearly 50 m. The largest stone arch in
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322 GREGG MARLAND AND ALVIN M. WEINBERG existence today is the Ponte Adolphe in Luxemburg, which was completed in 1903 with a span of 85.3 m. In 1758 the longest bridge span was a 120-m timber truss at Schaffhausen, Switzerland. In the United States, covered bridges were designed to protect the bridge deck and structure, particularly joints, from weathering. The life expec- tancy of early covered bridges was much enhanced by the development of paints and other preservatives. The longest timber bridge remaining in this country is a 140-m-long covered bridge built in 1866 on the border between Vermont and New Hampshire. As technological development continued in the United States, however, timber and stone gave way to metal and other materials. The nation's first cast-iron bridge was completed in 1836 in Brownsville, Pennsylvania; the first large bridge built of structural steel was the Eads Bridge in St. Louis, completed in 1874 with three 150-m arches. Concrete was first used in a U. S . bridge in 1871; in 1889 the first U. S. reinforced concrete bridge was built in Golden Gate Park, California, ushering in what the U.S. Department of Transportation (DOT) has called the "great bridge era" in the United States. This period between 1900 and World War II saw rapid growth in the number and size of bridges and in related technical knowledge, of which the most important was the development of rein- forced concrete (DOT, Federal Highway Administration, 19771. The first use of prestressed concrete in a U.S. bridge, the next major technical step forward, was in Philadelphia in 1951. Advances in design capability made it possible to improve the service- ability of bridges. Thus, by 1870 engineers were able to do stress and moment analyses for structural design. Today, the advent of computers has made possible even more refined analyses of more complex structures in less time. Our inheritance of older bridges in the United States includes many that continue to perform in exemplary fashion and many that continue to perform in spite of what we now consider to be inadequacies of one sort or another. The Federal Aid Highway Act of 1970 included a bridge replacement program. Seven years later, the U. S . Department of Trans- portation reported that, although many of the most deficient had been replaced, "There are thousands of bridges on the Federal-Aid system that are posted as having limited capacity of carrying truck traffic" (DOT, Federal Highway Administration, 1977, p. 442~. "Today, the city of Chicago owns, operates, and maintains more movable bridges than any other public agency in the world. Many of those existing structures are more than a half-century old, yet they continue to serve the purpose for which they were built.... That they can be taken for granted testifies to the excellence of the original design and to the never
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LONGEVITY OF INFRASTRUCTURE 323 ending inspection, maintenance, and repair program" (Christensen 1973, p. 1131. Roads Roads and trails on earth date to man's basic need to seek food and water. Long-distance routes were the result of the irregular distribution of important materials, such as flint, amber, tin, and silk. The most precisely determined of the prehistoric long-distance roads were those across west central Europe (for the trade in amber) dating back to 2000 B.C. Some ancient "ridgeways" in England, however, seem to have been in use for 6,000 years. The credit for building the first "made" road is generally given to the Romans, but well-made roads were built long before this time. There were probably stone roads in 3000 B . C. for hauling blocks for the Great Pyramid of Cheops (Gregory, 19311; and the Carthaginians are said to have made a system of stone-paved roads in the fifth century B.C., although no remains have been found. The Roman Empire prepared an entire continental system of well- built roads for administrative purposes; indeed, as Gregory (1931, p. 62) s a-id, "roads made the Roman Empire possible." The Itinerary of Antoine, published during the reign of Diocletian, consists of a list of 372 roads totaling 85,237 km in length. Some Roman roads in England still have paving in place, especially where they have been buried by soil or new roadways. Once routes are established, they tend to be preserved, although the utility of the road itself depends heavily on its maintenance. After the Roman army withdrew from England, maintenance was not continued, bridges collapsed, and roads were lost to use. Similarly, Gregory observed in 1931 that the imperial roads in many parts of China had fallen into decay through lack of repair. He noted, "It is said that in China a road is good for seven years and then bad for 4,000" (Gregory, 1931, p. 1071. Throughout history, good road maintenance has generally been the product of stable central and local authority. An early formal recognition of this truth came in 1555, when the English Parliament passed the first statute to put road maintenance under the control of elected authorities. The permanence of travel routes is nowhere more apparent than in the United States where the history of roads is relatively short. In the United States, we can document relatively easily the passage of a route from Indian trail to pioneer road to country road to modern highway. "In a host of instances our highways and roads follow for many miles the general line of the routes of the buffalo and Indian on high ground" (Gregory, 1931, p. 111. Although new demands and vehicles, new materials, and
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324 GREGG MARLAND AND ALVIN M. WEINBERG new construction and maintenance methods have continually forced changes on our roads, routes and rights-of-way have often been maintained. We notice repeatedly this continuity of basic major routes in spite of changing demands and minor route changes. The coastal highway, now U.S. Route 1, was substantially in place south to Charleston, South Car- olina, by the time of the War of 1 812. As reported by the U.S. Department of Transportation in 1977, There were over 2,350,000 miles of rural roads and city streets at the time of the advent of the automobile. .. . [Wlhat we have been doing for 73 years is highway improvement planning.... Most of the mileage added has been in the expanding suburban areas.... Most of the planning has been directed toward upgrading the early roads on or close to their original locations. Notable exceptions are seen in the Interstate System . . . and in . . . Alaska. (p. 264) As vehicles have evolved, becoming faster and heavier, roads have become obsolete because of inadequate alignment, grade, width, and sight distance. Many roadways have been upgraded and many relocated with the old roadway relinquished to local authorities. Narrow bridges and bridges with low load capacities, sharp curves, and unbanked turns have gradually been eliminated. Much new right-of-way has been required to straighten and widen roads. Insufficient capacity and the choking traffic of strip development have been other causes of obsolescence for long- distance routes. After a trend toward widening existing roads in the United States has come the development of special, high-capacity roads. In fact, the evolution of the nation's roads reflects their changing role in human affairs in addition to the changing technology of roads, road building, and road use. That role has been shaped by numerous influences including the development of bicycles and cars, concerns about mud and dust, conflicts between urban and rural interests, changing perspectives about who should pay for and maintain roads, safety considerations, the availability of im- proved building materials, and the evolution of quantitative engineering principles. Perhaps the most recent factors to play a major role in the evolution of roads have been the social, economic, and environmental aspects of the highway system. Chicago, like most cities, has struggled with the quality and capacity of its roads. The city was platted in 1830 with roads 66 feet wide, but this size has proved inadequate in many instances and there has been considerable restructuring. A citywide plan was developed in 1907 by Daniel Burnham, many parts of which were gradually implemented over the subsequent half century. When Michigan Avenue was widened be- tween 1914 and 1929, 8,700 property settlements were required, although many who received damages were surprised to find themselves rewarded in addition with increased property values. The "backbone of Chicago,"
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LONGEVITY OF INFRASTRUCTURE 325 the Eisenhower Expressway, was envisioned by Burnham but not com- pleted until 1956. Other events also mandated change in the city's streets; for example, the adoption of a sewage system plan in 1855 required raising the grade of many streets to provide the correct slope for the sewer system. Yet the continuity of routes in the face of changing styles, times, and needs, is exemplified by the Dan Ryan Expressway: The Vincennes Trace, carved out by the wheels of the early settlers' wagons, connected the pioneer village of Chicago with Vincennes, Indiana. The "trace" followed earlier trails formed by moccasined feet of Indians. The $300 million Dan Ryan Expressway, opened to traffic in 1962, retraced this ancient thorough- fare with multiple lanes of reinforced concrete. (Christensen, 1973, p. 158) Drawings from Robert Phillips in 1737 (Figure 15-2) show that the durability of road surfaces 250 years ago was not qualitatively different from that of modern roads. Gregory gives some hint of the life expectancy of road surfaces in 1931: waterbound macadam, 3 years; tar macadam, 9 years; asphalt macadam, 12 years. A 1949 national survey of the U.S. interstate system found that the average age of road surfacing was 12 years and that 13 percent of roads in the system were more than 20 years old and "nearing the end of their useful lives" (DOT, Federal Highway Administration, 1977, p. 1651. Griffin (1986, p. 52) writes that U.S. "interstates are designed to last 20 years before major repairs are necessary, but many do not." The quality of the road surface is rated "good" in only 57 percent of the interstate highway system; almost 10 percent is rated "poor." This is because of failure of the initial estimates to anticipate traffic volume, especially of heavy trucks. The damage from heavy traffic volume can be seen in New York City, which patched half a million potholes in 1985 (Bedard, 19861. HOW LONG COULD ELEMENTS OF INFRASTRUCTURE LAST? The foregoing examples show that the lifetimes of power plants, dams, roads, and bridges are distributed over a wide range. The Grand Teton Dam failed immediately when the reservoir was filled; the Alicante Dam remains serviceable after nearly 400 years. The Tacoma Narrows Bridge failed after 4 months; the Brooklyn Bridge still stands after 100 years. In many instances a power plant or a bridge is taken out of service not because it no longer can perform its original function but because a com- peting device can perform the same function less expensively or because the original function is no longer very useful for example, the bridge is too narrow for the increased traffic it must now carry. In the following paragraphs, however, the focus is on the narrower issue of physical ob- solescence or failure: Can we identify in the design and construction of
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326 GREGG MARLAND AND ALVIN Al. WEINBERG PLATE XIV. ~9 I. ~ Ohs no Fact Liz, ~ ~ ~9 '.~/~f. 7~ A day oz`~:f/~.e4 make .. . /69 3. J~z4r~ Me hand ~ Awed ~ 5Z`~ ~ turf Ohs t~ Yew Sty Hi. ~/~4~;f t/wfowr~ Mar a- ~w a. ~ I Mar FIGURE 15-2 The road's progress as predicted by Robert Phillips to the Royal Society, 1737. SOURCE: Gregory ( 1931).
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LONGEVITY OF INFRASTRUCTURE TABLE 2 Failure Frequency of Dams Years of Building 1850-1899 1900-1909 1910-1919 1920- 1929 1930-1957 Percentage of Dams Failing Within 20 Years of Construction 4.0 3.5 2.5 2.0 0.5 SOURCE: Germond (1977). 327 these structures trends that portend longer life for the coming generation of basic structures than for the previous generations? The answer is almost surely yes. A single instance of a Newcomen steam engine lasting for almost 150 years proves the existence theorem: Devices of this class can in principle last a long time. Research ought to reveal why they last a long time, and therefore research should lead to devices that are longer lived. For centuries, both dams and bridges were designed empirically. As designers learned the principles of mechanics and of the strength of ma- terials, the building of bridges and dams gradually became more scientific and catastrophic failures became less frequent (Table 15-21. This trend toward fewer catastrophic failures can be expected to continue as tech- nological innovation continues, bringing improved materials, better mon- itoring of the status of these devices, and improved design for the easy replacement of deteriorated components. Three examples illustrate these points. First, the steel used in the pres- sure vessels of older light-water reactors is sometimes sensitive to radiation embrittlement. The elimination of copper impurities in these steels is expected to increase their resistance to embrittlement. Second, the new St. Petersburg-Ft. Myers suspension bridge will be monitored extensively for stress and temperature by a system of sensors, all feeding information into a central computer. Such elaborate monitoring ought to give early warning and therefore help forestall incipient failures. Third, early pres- surized water reactors in nuclear plants were designed under the assump- tion that the steam generators would last as long as the plant. This has not been the case, and in addition, defective steam generators in these plants are awkward and expensive to replace. Reactor designers now realize that steam generators can be expected to fail and design them to be replaceable. In some sense, the longevity of these devices reflects the prejudices and traditions of their designers. Cathedrals in the Middle Ages were
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328 GREGG MARLAND AND ALVI1!l M. WEINBERG expected to be eternal. Because of this tradition, great care and expense went into their construction: many such cathedrals are now 500 or more years old, although most have been rebuilt and require extensive main- tenance. By contrast, roads in the United States have usually been perceived as having a short lifetime; in general, they have been built to last 20 years, whereas the autobahns in Germany are still serviceable 50 years after Hitler began their construction as military arteries. Of course, Hitler per- ceived his Third Reich as lasting 1,000 years. Albert Speer in his memoirs writes that in anticipation of such "immortality," he experimented with various concretes to determine their resistance to the elements. Power plants traditionally have been expected to last 25 to 30 years, largely because history has shown them to become noncompetitive by then, and their design was geared to this perception. Today that perception has changed, in part because the plants have reached a thermodynamic ceiling. As a result, some Russian reactors now are reported to be designed for 70-year lifetimes. The issue in some sense is always one of economics: the projected lifetime of a device can generally be lengthened if enough money is put into its construction. But if the perception of obsolescence is strong, then the amount that is worth spending in the first place is limited. A power plant, for example, must pay for itself over its lifetime. As that lifetime decreases, the amount we can afford to pay at the outset is lessened, and such penury by and large reduces the lifetime of the plant. One would expect that research and development in materials, moni- toring, and design ought to lead to devices that deteriorate slowly without requiring unreasonable additional capital investment. Indeed, R&D aimed at lengthening the life of infrastructure could be an important step toward improving our country's vital systems. HOW LONG SHOULD INFRASTRUCTURE LAST? As long as an element of infrastructure fulfills its function satisfactorily, economic forces will encourage its survival rather than its replacement. Once the structure or device has been amortized, it becomes a "free" good bequeathed by a prior generation to its successors. At that time the capital carrying cost of the old device falls to zero. Unless the maintenance and operating costs of the old device become so high that they exceed the combined fixed and operating cost of its replacement, it is less expensive to keep the old system than to replace it. Obviously, devices designed to be "immortal" are more expensive than throwaway devices. How much more expense is warranted to make a
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LONGEVITY OF INFRASTRUCTURE 329 device immortal can hardly be estimated in general. It can only be hoped that the cost of immortalization will continue to fall as our technology improves. A powerful argument against immortalizing infrastructures lies in our uncertainty about the future. Despite our most confident predictions we can never know how much a city will grow in the next 50 years. Thus, a magnificent bridge, built for immortality in 1880, may prove inadequate 100 years later, not because the bridge has deteriorated but because it has become a bottleneck to growing traffic. Arguments such as this underlie the recent trend toward smaller units in power plants. Because growth in a plant's electric load is so hard to predict (and the predictions of the 1970s have almost without exception been far too high), many utilities have responded by forswearing large (1,000 MOO), long-lived power plants for much smaller (~200 MW) plants. This stratagem sacrifices economy of scale to gain the reduced risk of guessing wrong on load growth. By choosing smaller plants, the utility maintains a flexibility it forgoes when it builds mammoth facilities that may require more than 10 years to build. Is there any evidence for what is perceived to be a growing reluctance to build new infrastructure in very large units and instead to emphasize smaller, decentralized elements, simply because the smaller elements al- low greater flexibility? We can only see such a trend clearly in the case of power plants. On the other hand, we cannot ignore the many trends in our social ethos that glorify decentralization and the idea that "small is beautiful." Should these trends continue to acquire political status, we might expect future infrastructure to be built on a smaller scale, to be more flexible, and possibly less longed lived. The connection between immortality and size is not clear. Many utilities install relatively small gas turbines that tend to have intrinsically short lifetimes. And in a rough way (approximate surface-to-volume ratio), a large bridge might be ex- pected to last longer than a small one. We cannot claim, however, to understand the relation between longevity and capacity. Nevertheless, there are powerful incentives to continue along the tra- ditional line of large, centralized, long-lived infrastructure. Many elements of infrastructure, especially power plants, emit pollutants. The treatment of pollutants is cheaper on a large scale than on a small one. Economics thus would favor the centralization of systems that deal with pollutants, including waste disposal facilities. A second incentive toward centralization of facilities is to be found in the current reluctance to accept any device that the public finds environ- mentally threatening, whether it is a dam, power plant, transmission line, or waste disposal facility. The situation is perhaps most clear-cut for power
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330 GREGG MARLAND AND ALVIN M. WEINBERG plants; no one wants a new power plant in their "back yard. " This suggests that new power plants, if they are to be built at all, are likely to be built on existing sites. Thus, even if the power-producing devices themselves are mortal, the sites are probably immortal. What is true of power plants is probably true of transmission lines and waste disposal facilities: their sites, once chosen, are likely to remain in operation long after the original devices have crumbled and decayed. It may be that the siting of new infrastructure, insofar as it requires new sites, will prove to be the most serious impediment to the renewal of our vital systems. Certainly the electric power industry's experience in the siting of transmission lines and of coal- and nuclear-fired generating plants gives us little assurance that the creation of future infrastructure will be easy and without political ferment. Perhaps this characteristic, more than any other, will argue for maintaining the existing infrastructure, or at least the existing sites, rather than arousing the passions of those who would be inconvenienced by, or who might even believe themselves to be susceptible to harm as a result of, new infrastructure. GENERAL OBSERVATIONS The challenge in the field of infrastructure is one of anticipation and optimization. If today a bridge is judged to be inadequate for whatever reason, this does not necessarily demean its functioning to date, nor does it justify construction of a bridge whose capacity will not be required until 50 years hence. On the other hand, if it appears that a bridge at this location will be a permanent part of our infrastructure, can we design it so that its physical structure and life expectancy are optimized for an evolving role, perhaps for incremental changes or periodic replacement? A further part of the challenge is that as items of infrastructure increase in size and complexity, the consequences of failure or misjudgment be- come greater. It is this sort of recognition that has led to the construction of electric power grids in such a way that service can be maintained despite the failure of part of the system and to highway repaving methods that permit one lane to remain open to traffic while the adjacent lane is re- surfaced. But how much flexibility is it possible to incorporate into our infra- structure? It has been pointed out that one of the dangers of long-term climate change (for example, as a consequence of increasing concentra- tions of atmospheric carbon dioxide) is that our infrastructure "grows up" dependent on the current physical environment. Hazardous waste presents a particular challenge. We are caught between our immediate, pressing need to do something with waste and the pos
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LONGEVITY OF INFRASTRUCTURE 331 sibility that in the future we will discover better ways for dealing with it. Certainly, for nuclear waste, it is necessary to design a system that has virtual immortality. As was pointed out for all the systems discussed in this chapter, designing for immortality implies both a well-engineered structure and a stable central authority to care for it. It is this kind of concern that has led one of us to contemplate something approaching a religious order that would harbor the long-term commitment to stewardship of waste sites. We can assert that one of the real problems in dealing with hazardous waste now is that we have done so poorly in the past, both in original engineering and in stewardship. CONCLUSIONS From this brief review of several elements of physical infrastructure, one is left with the impression that some elements last much longer than their expected design life whereas others do not. The energy-generating system, although it is aging, seems likely, by and large, to last longer than was expected. On the other hand, there is little evidence that roads, even modern ones, will last much longer than their design lifetimes- that is, unless they undergo costly repairs. Modern dams and bridges probably will last considerably longer, on average, than their design lives. What does seem clear is that even if the elements of infrastructure are themselves not "immortal," the sites that they now occupy probably are. This trend has been accentuated in recent years as popular opposition to new large and intrusive structures and processes has grown. This trend further suggests that the geographic backbone of our society is probably well established and is unlikely to change. REFERENCES Bedard, R. 1986. Car and Driver, August 1986, p. 56. Burwell, C. C., and J. A. Lane. 1980. Nuclear Site Planning to 2025. ORAU/IEA-80- 5(M). Oak Ridge, Tenn.: Oak Ridge Associated Universities, Institute for Energy Anal- ysis. May. Christensen, D., ed. 1973. Chicago: A History. Department of Public Works, City of Chicago. Chicago: Rand McNally and Co. Electrical World. 1985. How old are U.S. utility powerplants? (June): 103. Germond, J. P. 1977. Insuring dam risks. Water Power & Dam Construction. (June):36. Gregory, J. W. 1931. The Story of the Road. London: Alexander Maclehose Co. Griffin, L. 1986. The state of the interstates. Car and Driver, August 1986, p. 52. Hopkins, H. J. 1970. A Span of Bridges: An Illustrated History. New York: Praeger Publishers. Hudson, C.R. 1983. Age and Capacity Profile of Electric Generation Plants in the United States. ORNL/TM-8510. Oak Ridge, Tenn.: Oak Ridge National Laboratory. National Research Council. 1985. Technological Alternatives for Urban Infrastructure.
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332 GREGG MARLAND AND ALVIN M. WEINBERG Building Research Board, J. P. Eberhard and A. B. Bernstein, eds. Washington, D.C. National Research Council. Smith, N. 1972. A History of Dams. Secaucus, N.J.: The Citadel Press. Tennessee Valley Authority, Division of Water Control Planning. 1963. The Nickajack Project. TVA Report 44-100. Norris, Tenn. Tennessee Valley Authority, Hydropower Planning Section. 1983. Project Rehabilitation Feasibility Report, Great Falls Project. TVA Report WR28-1-13-101. Norris, Tenn. Tennessee Valley Authority, Office of Engineering. 1963. The Hales Bar Problem A Summary Report. TVA Report 44-4. Norris, Tenn. U.S. Department of Transportation, Federal Highway Administration. 1977. America's Highways 1776-1976: A History of the Federal-Aid Program. Washington, D.C.: U.S. Government Printing Office. Weinberg, A. M. 1985. "Immortal" energy systems and intergenerational justice. Energy Policy 13(1):51-59.
Representative terms from entire chapter: