Gifford Adaptability Urban Transportation Policy

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TECHNOLOGICAL FORECASTING AND SOCIAL CHANGE 45, 11 l-l 17 (1994)

ISSUES PAPER

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Adaptability and Flexibility in UrbanTransportation Policy and Planning

JONATHAN L. GIFFORD

ABSTRACT

The poor representation of uncertainty in the urban transportation planning process can lead to excessivelylarge and permanent facilities. Such inflexible facilities and systems may condition and severely constrain options

available to future generations for organizing the production, consumption, and distribution of goods andservices. The relationship between facility size and permanence and flexibility has received too little recognitionin practice and too little attention in research. This paper calls for increased research to provide policy makersand practitioners with a greater understanding of the consequences of the present approach and the advantagesand disadvantages of more flexible approaches.

IntroductionIn his history of city building since the early Middle Ages, Josef Konvitz [11 observes

that [bluilding too much too well has produced cities with many prematurely obsoletestructures and districts that conform to patterns which have been superseded by technolog-ical change. Especially in the twentieth century, he argues, city builders have focused

on the city as an object of design. In earlier times, the city was a byproduct of socialand economic activity, relying on vernacular architecture and transient structures anddistricts that could be modified as social, economic, environmental, and technologicalconditions evolved [2].

Konvitzs argument poses a challenge for the planning of cities and their infrastructuresystems. Most city planning focuses closely on the city as an object of design, and itsorigins in the City Beautiful and other nineteenth-century reform movements are partof the canon taught to every planning student. Infrastructure planners from the civilengineering tradition focus on planning over horizons that derive more from the longevity

Dr. GIFFORD is an assistant professor in the Department of Public and International Affairs and a researchfellow in The Institute of Public Policy at George Mason University, He received his Ph.D. in transportationengineering with minors in city and regional planning and economics from the University of California, Berkeley.The current article draws on his book Flexible Urban 7iunsporation Systems, currently in progress.

Address reprint requests to Professor Jonathan L. Gifford, Department of Public and International Affairs,George Mason University, Fairfax, VA 22030.

0 1994 Elsevier Science Inc. OO40-1625/94/$7.00


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of engineering materials than from a facilitys functional service life, the assumptionbeing that facilities will be useful for as long as they last. It is a grave matter if infrastructureplanners are engaged in the design of facilities that will be poorly suited to future condi-tions and may impoverish future generations with the cost of maintaining them.

Central to this challenge is the issue of uncertainty. How much uncertainty is thereabout future conditions? If uncertainty is great, the rational policy is to avoid irreversibledecisions, maintain flexibility, and collect good intelligence. If uncertainty is modest, therational policy is to design to achieve long-run economies of scale [3].

The scope of this challenge encompasses the whole range of urban infrastructuresystems-sewer, water, transportation-and services-schools, police, fire prevention. Itsthorough investigation should entail extensive empirical studies in a variety of functionalplanning areas to understand the trade-offs between long-term operating efficiencies andshort-run flexibility. The goal of this paper is much more modest: to consider Konvitzs

ideas in the context of urban transportation planning, and to identify research areas thatcan inform policy and public debate.

The paper examines the representation of uncertainty in urban transportation plan-ning and the relationship between uncertainty representation and facility size and longev-ity. Comments follow on the possible impact of these conditions on the adaptability andflexibility of urban transportation systems in the face of unpredictable social, environmen-tal, economic, and technological conditions, and avenues for future research.

The Extent of UncertaintyUncertainty is pervasive in the urban transportation planning problem domain. The

present and historical distribution of demand, for example, while observable in the field,is not well documented in most urban areas. The high cost of data collection leads plannersto rely on heavily massaged and derived data sources, which themselves introduce uncer-tainty into the planning and decision making process. Future conditions are uncertainbecause they are inherently random [4]. The future distribution of transportation demandwith respect to location, time of day, purpose, mode, and vehicle size and weight arehighly uncertain. Uncertainty also resides in the future location and characteristics oftransportation facilities and services. The delivery of transportation facilities and servicesdepends on a complex and fragmented set of institutions, each facing its own uncertaintiesand exigencies about the availability of funds, the willingness of elected officials to supportparticular facilities, and the publics willingness to allow construction to proceed. Thus,

planned facilities may never be built, or may be built to radically modified designs andcharacteristics of service.

The Representation of UncertaintyThe treatment of uncertainty in the urban transportation planning process has long

been a concern. One account [5] finds its origins in the economic literature of the 1960sconcerned with demand uncertainty for publicly provided goods [6]. In the 1960s and197Os, concern over uncertainty in transportation planning continued in the work of,among others, Manheim [7-91. The World Conference on Transportation Research tookthat topic as its theme in 1977 [lo].

The regional transportation planning process in the U.S. does recognize that uncer-tainties exist, and attempts to account for them at some level. Best practice suggests thedevelopment of regional scenarios, perhaps five or six, that capture at least broadly thelikely range of future conditions (e.g., see [l 11). Scenarios attempt to capture possibleor likely futures with respect to broad, largely exogenous forces such as economic growth,labor force participation rates, and economic structure. For each scenario, a plan isproduced.


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While scenarios capture-at least crudely - uncertainty about largely exogenous fac-tors, much deeper and more pervasive uncertainties are invisible in the planning process.The process is extremely data intensive. It requires, among other things, zonal distribu-tions of population and employment, trip generation rates, land use plans and restrictions,preferences of elected officials, and estimates of community acceptance of particularfacilities.

These data inputs are each uncertain. Elected officials change, often on a very shortcycle, bringing modified or even reversed political interests to bear. Comprehensive plansare revised less often, but often dramatically, thereby changing specified levels of zonalemployment, population, and traffic generation. A communitys preferences and willing-ness to accept the construction or expansion of particular facilities also varies unpredict-ably over time, as does its willingness to provide operating subsidies for public transit.

Moreover, the current and historical data on which future estimates are based arethemselves generally derived from infrequent-sometimes very infrequent-surveys andmeasurements of transportation behavior. Traffic surveys that form the foundation ofthe future estimates are often a decade or more out of date. They are adjusted andmodified to reflect current conditions, to be sure. But these adjustments themselves intro-duce additional error. Also, trip generation rates vary significantly within and amongregions; yet the cost of data collection, and the time required to assemble and synthesizeit, generally preclude the collection of new, accurate data.

Despite concern over the treatment of uncertainty, there is no systematic body ofdata indicating how uncertainty is treated in practice in the field of transportation plan-ning. Some anecdotal evidence is suggestive, however. Federal regulations stipulate fairly

uniform planning procedures as conditions of federal grants, and the traditional regionaltransportation planning approach has been common to most metropolitan transportationplanning activities in the U.S. since the late 1960s (see [12]).

The Impacts of Poor Uncertainty RepresentationGiven the extent of uncertainty in urban transportation planning and its poor repre-

sentation in the decision process, what are the likely impacts on the design of transporta-tion facilities?

Theory clearly shows that ignoring risk about future conditions leads to the specifica-tion of larger projects or facilities [13-161. Pearman summarizes the argument well:[i]n a dynamic decision making environment where knowledge increases over time, [if]

irreversible projects with uncertain streams of returns are compared in terms only oftheir expected values as viewed at the present [i.e., if uncertainty about future conditionsis ignored], there will be a significant tendency for such irreversible decisions to be takenprematurely (ref. [5], p. 432). Furthermore, ignoring demand uncertainty can lead toupward biases of optimal capacity estimates, even in the presence of significant economiesof scale such as are exhibited in the case of water supply [17, 181.

Some analyses of the traditional four-step planning process suggest that the assign-ment step-where zone-to-zone travel is assigned to specific routes-is relatively robustwith respect to errors in the earlier stages of trip generation and distribution due to theaggregative nature of the assignment process, as long as the average trip length remains

constant. That is, even relatively large errors in the estimation of spatial demand distribu-tions essentially net out in the assignment process as long as the average trip distributiondoes not change. According to this argument, uncertainty about future spatial demanddistributions should not undermine confidence in the traditional approach, since evenrather different distributions yield quite similar route assignments [19-221.

While these analyses are reassuring, their limitations are not completely benign, asChang 1221 has acknowledged. First, the aggregative nature of the assignment process -


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that is, the fact that all metropolitan travel shares the same network of facilities-iscontingent upon the density of the network under consideration. The denser the networkbeing considered, the less aggregative the assignment process, and-one expects-themore sensitive it will be to variations in travel distribution. For example, in the degeneratecase of a linear city, where all travel occurs along portions of a single highway, one caneasily imagine that aggregate levels of travel on that highway would be somewhat insensi-tive to minute variations of zone-to-zone travel demand. At the opposite extreme, on anetwork that provided a separate facility for travel between each zone pair-that is, acompletely nonaggregative network-travel on each link would obviously be highly sensi-tive to the demand for travel between its associated zones.

A second limiting assumption is that assignments do not vary much as long as averagetrip lengths remain the same. Again, this has some intuitive appeal as long as averagetrip lengths are large relative to the size of the metropolitan region. As trip lengths decline,however, one would expect the assignment to become increasingly sensitive to variationsin spatial distribution. Consider the extreme case where average trip lengths are muchsmaller than the dimension of a single zone, suggesting that most trips occur within onezone. One can easily imagine sets of travel distributions having such an average trip lengththat would give rise to rather different traffic assignments. Moreover, recent analyses haveconfirmed the continuing decline in average trip lengths in major metropolitan areas[23, 241.

In the context of uncertainty representation and its effect on facility size, the tradi-tional process would appear to provide unbiased guidance only under fairly tightly con-strained conditions, namely, a sparse network of major arterial highways. If a broaderrange of network configurations is brought into consideration, the traditional processwould appear to be subject to the biases for premature project constuction and for facilityoversizing introduced earlier. Failure to consider uncertainty about future conditions canlead to premature deployment and oversizing of facilities. Conditions under which thetraditional process nets out these uncertainties in the assignment process appear to belimited in their applicability.

Implications for Urban Transportation PlanningConsider the implications of poor uncertainty representation for urban transporta-

tion planning. Konvitzs original observation was that cities are too durable. The foregoingdiscussion has introduced a logical connection between durability and uncertainty in thedecision process, drawn from the economic and policy literatures.

This reasoning suggests that, ceteris paribus, if uncertainty were accurately repre-sented in the urban transportation planning process, projects would generally be smallerwith shorter design lives. But how do these general observations apply to urban transporta-tion particularly? Do they imply building disposable highways or, for that matter,disposable cities, and all that implies about resource utilization and sustainability? Ifuncertainty militates against designing and building for the long term, what is the appro-priate role for the transportation planner?

Elected decision makers tend towards relatively short time horizons: the next election,

typically two to four years. Not all operate on such short horizons, of course, but theincentive structure is not designed to focus on the long term. Planning agencies, throughcomprehensive planning among other techniques, attempt to insert a longer-term focusinto the decision process. But comprehensive plans and zoning laws to enforce them mustbe adopted by elected officials, thus subjecting them to the short-term orientation ofelected officials as well. Further diluting concerns for the long term are zoning variance


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requests, which may act as a loophole for developments that are inconsistent with theofficial long-term view. Thus, the urban planner and the urban transportation planner

are mightily pressed to respond to the challenges of the present.Comprehensive plans and transportation plans provide a bulwark for resisting exclu-sive attention to the here and now. Yet these plans rely for their legitimacy on subjectivenorms that may not stand up well over time; that is, they may themselves be of uncertainvalidity. Consider, for example, the separation of land uses, long a cardinal principleof urban planning, now largely debunked. This norm has had enormous influence onthe development of American cities, so that the land use patterns in many cities bear astrong imprint of an obsolete planning norm that constrains their ability to adapt tocontemporary conditions. A current favorite in some circles is jobs-housing balance,whereby housing and commercial land uses are located in close proximity, in direct contra-

vention of the previous norm of separation.While not without merit, such objectives do not incorporate a desire to preserveoptions in the face of uncertain future conditions. On the contrary, they aim for a specificset of solutions that make sense in terms of currently perceived problems and opportuni-ties. They act to reduce uncertainty by foreclosing options. Separation of land uses, forexample, protects a subdivision from incompatible uses on adjacent parcels, therebyproviding security to the homeowner. But the price of that security is a loss in flexibilitythat does not appear in the decision process.

Thus, uncertainty can be mitigated by constraining future options and giving stake-holders property rights over those options. Long-term concerns about flexibility and

adaptability of the city to inherently random future economic, social, environmental,and technological conditions and opportunities receive little recognition in the decisionprocess. All parties operate under an illusion that the future is knowable and controllable,and that the important thing is to protect and advance their own interests. The challengein planning, then, is how to mediate between the short-term exigencies of democraticpluralism and the longer-term, but questionable, norms of planning.

An alternative approach would focus on postponing irreversible decisions as longas possible and keeping their scale to a minimum, identifying and preserving options,and collecting good intelligence. This is a markedly different approach to planning,whether urban planning generally or transportation planning particularly.

Does this approach imply disposable highways or disposable cities? It does insofaras it sees each project or facility as serving only transient purposes. On the other hand,it is resource conserving insofar as facilities would use no more of a resource than requiredto serve near-term and relatively certain demand, with the potential of being supersededor replaced later. The replacement would presumably be designed to meet contemporarysocial, economic, environmental, and technological conditions.

Such an approach is at odds with other players in the urban development game whoare generally not willing to invest until government has made an irrevocable commitment,be it to a road for access or a zoning law for controlling adjacent uses. Homeowners,developers, and banks would surely question government flexibility with respect to theprovision of public facilities and services and land use restrictions. Moreover, forces forreform of current problems are pressing for less flexibility, not more, in the form ofadequate public facility ordinances and growth management (see, e.g., [25-281).

Concluding Remarks and Research RecommendationsThe poor representation of uncertainty and its impact on project scale and durability

raise important questions that deserve serious consideration by those who plan and build


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our cities and their transportation systems. Together, these considerations call for moreflexibility in the planning and development of urban transportation infrastructure.

Yet while concerns about flexibility in urban transportation infrastructure may bein order, the unanswered question is how such flexibility might actually be incorporatedinto an ongoing infrastructure planning and development program, or might replace anongoing infrastructure program with something that is much more attuned to flexibility;for it may be the case that more radical change than can be achieved by mere fine-tuningof existing programs is in order.

Consider that urban infrastructure planning in the U.S. and, to a large extent, inthe developed nations of the world, derives from Renaissance and nineteenth centuryassumptions about the existence of an underlying order to the universe, whose revelationthrough scientific observation and study was the task of engineers and planners. As longas the engineer sought to reveal an externally defined order, a divinely inspired orderin many views, then there was no need to question the legitimacy and desirability ofthat order.

But contemporary philosophers, mathematicians, and scientists tell us increasinglythat much of the apparent order we observe in everyday life is in fact merely transitory,the occurrence of fairly predictable behavior between aperiodic structural changes orbifurcations in complex processes whose long-term trajectories are difficult to predict.Herein lies a research challenge to the infrastructure planning community. What sortsof change in planning institutions and processes, whether radical or incremental, areavailable to policy makers, and what are their merits?

It may be the case that while inflexibility imposes social costs, in fact those costsare outweighed by the benefits that flow from the investments. Yet how are we to makethat calculation, especially in light of the fact that the very estimates of costs and benefitsupon which such an assessment would be based are themselves forecasted values thatare highly uncertain and subject to heroic assumptions about the nature of future techno-logical opportunities, environmental constraints, economic conditions, and social prefer-ences? To what extent are systems and facilities developed using voluntary investmentrather than compulsory taxation more or less flexible?

Of course, it is appropriate to attempt to use infrastructure to establish an orderedenvironment in which households and firms can attend to other concerns, if the orderso established is one that facilitates well being. But how is that to be determined, andby whom? That is the central question; through government and collective action, throughprivate, voluntary action, or in what combination of public and private action?

These fundamental questions have received far too little attention in research oninfrastructure policy and planning. Yet they are important, and further, not impossibleto research. Comparative infrastructure planning and management can examine the meritsof various approaches, across national and continental boundaries as well as across vari-ous technologies. Yet with few exceptions, little research has focused on this issue. Varia-tions in the flexibility and adaptability of alternative planning and management ap-proaches may be difficult. But variations, even in the U.S. context, are certainly available:federal provision of service (air traffic control and waterway); federal capital aid to states

and localities (wastewater treatment, transit new starts, and highways); regulated privateutility (pipeline, telecommunications). As society examines the merits of improvementsin existing systems (such as intelligent vehicle highway systems) and the deployment ofnew systems (such as maglev and the information superhighway), such research caninform-and should inform-decisions about the institutional and technical nature ofplanning and development activities.


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Received 29 March 1993; revised 2 August 1993

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