Cities and Their Vital Systems Infrastructure Past, Present, and Future (1988) / Chapter Skim
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8 Dynamics and Replacement of U.S. Transport Infrastructures
8 Dynamics and Replacement of U.S. Transport Infrastructures
Pages 175-221
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From page 175... ...
As the examples will show, both the growth and senescence of transport infrastructures evolve as regular processes, which are describable by S-shaped logistic curves. Not all growth and senescence phenomena can be described by simple logistic functions, however.
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From page 176... ...
Analysis of the historical development of these two systems will include a quantitative description of performance improvement, the general evolution of a particular infrastructure, and the replacement of old technologies and infrastructures by new ones in terms of their relative market shares. The term performance is used as a multidimensional concept (i.e.
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From page 177... ...
177 The logistic function has been fitted to the actual data, and it indicates that the inflection point in the growth of air carrier operations occurred about 10 years ago (around 1977~. Thus, after a period of rapid exponential growth, less than one doubling is left until the estimated saturation level is achieved after the year 2000.
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From page 178... ...
Transformed in this way, the data appear to be on a straight line, which is the estimated logistic function.] Perhaps the most interesting result is that it took about 30 years for world air transport to reach the inflection point (about half of the estimated saturation levelly and that within two decades the saturation level will be reached.
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From page 179... ...
The analogy between air transport systems and electrical grids or road systems is very close: large aircraft correspond to high-voltage transmission lines or primary roads. Figure 8-3 shows the improvement over time of one important performance indicator for commercial passenger aircraft: carrying capacity and speed (often called productivity)
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From page 180... ...
Another interesting feature of Figure 8-3 is that the productivity of all passenger aircraft is confined to a rather narrow band between the performance feasibility curve and a "parallel" logistic curve with a lag of about nine years. This logistic curve represents the growth of world air transport from Figure 8-2.
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From page 181... ...
Thus, at saturation, structural change will occur, leading to a new growth pulse (probably S-shaped) and in turn to new productivity requirements and therefore to supersonic or hypersonic transport.
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From page 182... ...
in 1906, and the last is the American Wright Turbo Compound, rated at 3,400 hp in 1950. These engines represent an improvement in power of almost two orders of magnitude over 44 years and about 90 percent of the estimated saturation level for piston engines (about 3,800 hp.)
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From page 183... ...
The time constant for the development of passenger aircraft is therefore about 30 years. Thirty years after the standard industry design emerged during the 1930s, the B-747, the first wide-body jet to enter service, became one of the most significant improvements in commercial transport, and its productivity represents half of the estimated industry saturation level that may be approached toward the end of this century.
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From page 184... ...
The working hypothesis in this case is that the two trends indicate two different phases of the dissemination of motor vehicles in the United States. The first characterizes the substitution of motor vehicles for horse-drawn road vehicles, and the second the actual growth of road transport after animal-drawn vehicles essentially disappeared from American roads (see Nakicenovic, 19861.
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From page 185... ...
Although estimates of nonfarm horses and mules are not very accurate and are unevenly spaced in time, Figure 8-6 indicates that the automobile replaced horse- and mule-drawn road vehicles during a relatively short period and that the substitution process proceeded along a logistic path.3
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From page 186... ...
Because the growth of road transport in general and the substitution of automobiles for horse-drawn carriages and wagons overlap in time, together they produce two growth trends in the automobile fleet with an inflection point in the 1930s marking the structural change in the composition of the road vehicle fleets. The growth of all road vehicles results in one single logistic trend, however.
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From page 187... ...
. This figure shows that the growth of surfaced roads paralleled that of all road vehicle fleets while the total mileage of all roads remained almost unchanged.
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From page 188... ...
The dashed logistic function represents the growth in the number of all road vehicles from Figure 8-7. Thus, surfaced roads, as an important infrastructure for road transport, appear to be in the saturation phase today; the automobile fleet, on the other hand, is still growing and should reach its saturation phase in about 50 years.
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From page 189... ...
The dashed line shows the growth in the number of all road vehicles, from Figure 8-7.
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From page 190... ...
By 1835 three Boston railroads were in operation one to Lowell, one to Worcester, and the third to Providence. To some extent the early railway lines were feeder lines for canal and waterway transport systems in much the same way that the early commercial motor vehicles were feeders for railways.
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From page 191... ...
For example, sailing ships, wood fires, and horseback riding have all become favorite leisure time and sporting activities even though they were replaced by new technologies long ago. In this way, railways may be put to new uses perhaps for local passenger and tourist traffic similar to ocean cruises despite their insignificance as a mode of intercity passenger travel.
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From page 192... ...
At the same time the energy sources also changed. The draft animals used in the first tramways were replaced by steam locomotives fired by wood, which remained the principal fuel of railroads until about 1870 (Schurr and Netschert, 19601.
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From page 193... ...
Both growth processes are characterized by a At equal to about 50 years, but the inflection points of the two growth pulses are separated by 56 years the main tracks reached half the saturation level in 1890 whereas surfaced roads reached that point in 1948. Thus, the growth of these two infrastructures is characterized by a time constant of about 50 years, but the decline of railroad infrastructure appears to have been a much slower process.
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From page 194... ...
Thus, it is difficult to compare the total length of the implicit air and waterway routes and the total length of main railroad tracks or surfaced roads. For both air and waterway routes, however, there are abstract measurements that would, in principle, correspond to the length of the grid: the network of certified route carriers or federal airways in air transport and the total length of continental waterways and canals.
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From page 195... ...
In both cases the growth in mileage of the operated infrastructure increased rapidly, but after saturation the decline was far less rapid. Figure 8-13 shows the increase in the length of canals in the United States as a logistic growth pulse with a saturation level of about 4,000 mi after the 1860s.
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From page 196... ...
From this perspective the substitution of the four systems over time appears as a regular process.4 Several invariant features are inherent to this substitution process. At any given time, at least three important transport infrastructures are competing for shares of the total route length of all transport modes.
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From page 197... ...
This result may appear to contradict the earlier observation that the total length of railway tracks and surfaced roads took longer to construct than water and airway routes. In fact, the timetable associated with the substitution dynamics of infrastructure lengths is surprisingly consistent in relation to the duration of growth pulses of the four transport modes during the past 180 years.
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From page 198... ...
The saturation and decline of market shares therefore precede saturation in absolute growth in an increasing market, meaning that the eventual saturation of any competing technology can be anticipated in the substitution dynamics in a growing market. Although the substitution of younger for older modes of transport is a regular process when measured in total mileage of the four transport infrastructures, it is nevertheless only a proxy for the real dynamics of transportation systems, which should be measured in some common performance unit.
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From page 199... ...
To show that this is not a feature unique to the evolution of transportation systems, the next section of this chapter describes a similar regularity in the evolution of energy systems. Furthermore, future developments in transport infrastructures are related to likely changes in the energy system, especially with respect to energy transport and propulsion for prime movers.
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From page 200... ...
I NUC1°ar 1 950 FIGURE 8-16 Primary energy consumption in the United States. menu (by present standards)
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From page 201... ...
Energy Substitution Although for almost two centuries energy consumption did not draw equally from all sources and the use of all energy sources did not increase equally, primary energy consumption (including fuelwood) increased exponentially at an average growth rate of about 3 percent per year.
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From page 202... ...
This was observed in the substitution of canals, railway tracks, surfaced roads, and airways (see Figure 8-14~. During the 1970s crude oil was close to achieving a 50 percent share, but before actually surpassing this mark it began to decline.
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From page 203... ...
The future potential competitors of natural gas, such as nuclear or solar energy, have not yet captured enough market shares to allow definitive estimation of their future penetration rates. The starting point for market penetration of nuclear energy was the 1960s, when nuclear power acquired slightly less than a 1 percent share of primary energy.
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From page 204... ...
Indeed, pipelines are becoming an important freight transport mode, with market shares in total ton-kilometers per year comparable to those of train and truck transport. They are also comparable to railways in total length of the infrastructure or grid: the 200,000 mi of main railroad track in the United States are slightly shorter than the 230,000 mi of crude oil pipelines.
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From page 205... ...
By 1878 both crude oil and natural gas held more than a 1 percent share of primary energy consumption, but at that time most of the natural gas was consumed in the vicinity of the oil fields. The natural gas pipeline network began to expand rapidly during the 1890s, or about 20 years after the oil pipelines began to expand.
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From page 206... ...
The growth pulse started when oil achieved a 1 percent share of primary energy, inflection occurred when oil became the second largest energy source (by passing fuelwood) , and saturation of pipeline length was synchronous with the saturation of market shares.
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From page 207... ...
Considering the poor quality of the historical data on the growth of transport infrastructures, it is remarkable that four network or grid transport systems-railway tracks, surfaced roads, and oil and natural gas pipelines-cluster even more densely between 54 and 59 years. The time constants for canals and performance improvements in aircraft transport are shorter, about 30 years.
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From page 208... ...
Thus, growth processes that follow the simplest possible pattern a single S-shaped path can be difficult to measure even when they are almost complete because the saturation levels are a priori unknown and have to be estimated from the data. Technological substitution processes are inherently more complex because market shares of all important (competing)
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From page 209... ...
The evolution of these energy transport infrastructures, then, parallels changes in the energy system, but at the same time their growth patterns are no different from those of other transport infrastructures. A general conclusion is that technological changes, such as the substitution of road vehicles or locomotives, last a few decades; changes in the transport system and evolution of infrastructures, on the other hand, are longer processes with time constants of between three and seven decades.
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From page 210... ...
APPENDIX Estimation Methods for the Logistic Growth Function This analysis of the development of transport infrastructures and systems was based on the hypothesis that technological growth and substitution processes can be described by the logistic function. In the simplest case the logistic growth function describes the technological life cycle from the early development phase through the rapid growth and expansion phase to the eventual saturation phase.
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From page 211... ...
~ ~ = cat + (2, This is a convenient form for showing the logistic growth process on semilogarithmic paper because the historical data indicate a linear secular trend (assuming that K can be estimated from the data or that it is a priori known)
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From page 212... ...
Fisher and Pry used the two-parameter logistic function to describe a large number of technological substitution processes. They assumed that once substitution of the new for the old had progressed as far as a few percent, it would proceed to completion along a logistic substitution curve fats At ~ = at + ~ (3)
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From page 214... ...
The current saturating technology is then left with the residual market share and is forced to follow a nonlogistic path that curves from growth to decline and connects its period of logistic growth to its subsequent period of logistic decline. After the current saturating technology has reached a logistic rate of decline, the next oldest technology enters its saturation phase, and the process is repeated until all technologies but the most recent are in decline.
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From page 216... ...
is now the estimated fractional market shares of technology i. Because such a logistic function does not capture the saturation phases and represents only growing or declining logistic trends, n Ifi(t)
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From page 217... ...
Thus, initially, there are n- 1 technologies denoted by indices i ~ j that follow logistic substitution paths, and one technology, j, that reflects the residual of the market that is, the complement of the sum of other technologies and 1. Based on the point in time, tj, at which technology j is defined as a residual, application of the linear transform of the logistic function to the market shares of technology j, defined above, produces a nonlinear function that can be written in the form of equation (59.
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From page 218... ...
Figure 8-20 is a flowchart of the algorithm that describes the logistic substitution process. A more detailed description of this procedure and the software package for the generalized logistic substitution model is given in Nakicenovic (1979, 1984~.
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From page 219... ...
Thus, the presence of some linear trends in Figure 8-14 indicates where the fractional substitution of transport infrastructures follows a logistic curve. In dealing with more than two competing technologies, the Fisher-Pry model must be generalized because in such cases logistic substitution cannot be preserved in all phases of the substitution process.
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From page 220... ...
(as the ratio of the market share taken by a given energy source over the sum of the market shares of all other competing energy sources)
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From page 221... ...
1946. A Reappraisal of the Forest Situation, Potential Requirements for Timber Products in the United States.
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