A Case Study of Planning

The facts, figures, and inferences in chapter 7 regarding municipal behavior toward transit-oriented housing opportunities illustrate many points. Still, there is much that even a careful statistical analysis might miss or misunderstand. For that reason, we also explored what we could learn by talking to real planners about these issues. The case of San Diego is interesting and useful for several reasons. First, the San Diego Trolley is the oldest of the current generation of light rail projects in the United States. Unlike many newer systems, the age of San Diego’s rail transit (the South Line opened in 1981) allows time for land use planning to respond to the fixed investment. Second, the San Diego system is no stranger to modern transit-based planning ideas. The San Diego City Council approved a land-use plan for their stations that includes many of the ideas promoted by transit-oriented development (TOD) advocates (City of San Diego, 1992). Third, the light rail transit (LRT) authority in San Diego County, the Metropolitan Transit Development Board (MTDB), is often regarded as one of the more successful municipal LRT agencies. The initial parts of the MTDB rail transit system were constructed strictly with state and local funds, using readily available, relatively low-cost technology (Demoro and Harder, 1989, p. 6). Portions of San Diego’s system have high fare-box recovery rates, including the South Line, which in its early years recovered as much as 90 percent of operating costs at the fare box (Gómez-Ibáñez, 1985). All of these factors make San Diego potentially a “best-case” example of TOD implementation. When generalizing from this case study, it is important to remember that the transit station area development process in San Diego is likely better developed than in many other urban areas in the United States. The results from San Diego County can illustrate general issues that, if they have not already been encountered, might soon become important in other urban areas with rail transit systems. Also, given San Diego County’s longer history of both LRT and TOD when compared with most other regions, any barriers identified in San Diego County might be even more important elsewhere.

Transit-Oriented Planning

There has been a boom in American rail transit construction in the past two decades. That new investment has prompted the question of what planners can do to support rail transit. One popular answer has been transit-oriented development (TOD), increasingly described as a comprehensive strategy for rail-based land-use planning throughout an urban area. This is most clearly illustrated by Bernick and Cervero’s (1997) description of how such projects can link together to create “transit metropolises” where rail is a viable transportation option for many of the region’s residents. In addition, TOD provides an opportunity to examine the regulatory issues discussed in chapter 6, both because it is an explicit attempt to use urban design as transportation policy and because the intergovernmental issues are especially stark in relation to these developments. Having discussed how travelers behave in the first part of this book, we now ask what we know about how cities behave. Stated in general form, the question is rather broad. It concerns the process by which cities and other land-use authorities decide where to put streets, how to structure the local hierarchy of streets, when to develop more or less densely, how to position employment centers relative to residential areas, and so on. Still, the feasibility of land-use plans with transportation goals depends critically on how such authorities behave. Any discussion of the effectiveness of these strategies must address both how communities plan for transportation and how travelers respond to those plans. The primary transportation goal of TOD generally, as currently practiced, is to coordinate land-use policies to support rail transit. In particular, focusing both residential and commercial development near rail transit stations is aimed at increasing rail ridership (e.g., Bernick, 1990; Bernick and Hall, 1990; Calthorpe, 1993; Cervero, 1993; Bernick and Cervero, 1997). Some evidence suggests that residents near rail transit stations are two to five times more likely to commute by rail when compared with persons living elsewhere in the same urban area (Pushkarev and Zupan, 1977; Bernick and Carroll, 1991; Cervero, 1994d).

Studies of Urban Form and Travel

Does the built environment affect how often and how far people drive or walk or when they will take the bus or the train? If so, how? A lively, expanding literature continues to investigate the potential for causal links between urban design and travel behavior, yet there remain many gaps and considerable disagreement. Our purpose here is mainly to identify what past research has to say on these questions. We also try to explain why these studies reach different conclusions and how and where this work might be usefully improved. The first, and perhaps best-known, group of studies on this topic investigates how travel behavior and travel investment affect land use. There is also a long if more recent practice of viewing these links from the opposite direction; that is, how does land use influence urban travel? We consider this second question in more detail following a brief review of the first. Though not our focus, most questions about land-use/transportation links over the past century concern the influence of transportation infrastructure on development patterns. Analysts ask how highways and mass transit contribute to decentralization trends, how they affect the local balance of jobs and housing, or how they affect the pattern of commercial investment (see, e.g., the reviews in Gómez-Ibáñez, 1985b; Giuliano, 1989, 1991, 1995a, 1995b; Cervero and Landis, 1995). The basic idea is this: People choose their homes and locate their businesses based in part on their proximity to work, other potential destinations, and the markets for their products and labor generally (see, e.g., Von Thunen, 1826; Weber, 1928; Losch, 1954; Alonso, 1964; Muth, 1969; Mills, 1972; Solow, 1973; Fujita, 1989; Anas, Arnott, and Small, 1997). That is, the cost of transporting people and things over space depends on the distances and resources required. Once these costs are fixed, perhaps by the establishment of a central downtown or transshipment point, the price of land at each location is determined by demand. This in turn is determined, again in part, by how much money one has left after accounting for the transportation costs associated with that location.

Lessons for Research and Practice

Transportation problems seem to offer no end of interesting policy wrinkles and technical challenges, but despite the promise of each new technological innovation, financial windfall, and dazzling social science breakthrough, planners have not fared well. Air pollution, fuel, and traffic congestion costs continue to mount to where the benefits of making any headway appear substantial. Yet as more freeway lanes are dedicated to car-poolers and tollways, and new transit systems continue to soak up many billions of dollars, getting people to “improve” their driving behavior remains the ultimate planning brick wall. Increasing evidence suggests that transportation demand management schemes have extremely limited effectiveness, in the sense that only marginal and perhaps even cost-ineffective changes can be expected from most of the tools applied thus far. One view is that the planner’s arsenal of transportation demand management tools has proven largely ineffective in dealing with traffic congestion especially. The somewhat more optimistic account of some planners and architects is that attention has been focused on symptoms rather than the disease itself. As discussed in chapter 1, the vanguard of such urban design schools as the New Urbanism, Neotraditional planning, and transit-oriented development collectively argue that the way we organize space has profound implications not only for traffic patterns but perhaps also for our sense of self and modern civilization as a whole. Prominent urban designers, planners, and political leaders forcefully claim that these development strategies will, among other things, improve traffic conditions, reduce home prices, and generally increase the quality of residential life. Of course, this is just talk. As bold and stirring as these claims may be, they are mainly meant to get us thinking afresh about where and how improvements can be made—not as cold hard facts. Most transportation planners probably recognize that blanket statements of this nature are overly simplistic. Even the architects and planners promoting these ideas are usually careful to emphasize the many ingredients necessary to obtain desired results: the straightening of streets to open the local network, the calming of traffic, the better integration of land uses and densities, and so on.

The Demand for Travel

As described in chapter 1, the new urban designs are part philosophy, part art, part economics, and part social optimism. Still, a key to their popularity is the open embrace of conventional and even conservative standards of neighborhood form, scale, and style. Many new urban designs self-consciously recall small town settings where neighbors walk to get a haircut and stop on the way to chat with neighbors sitting on the front porch watching the kids play. The attraction of these ideas is subjective, personal, yet pervasive. After all, in principle, what is not to like about pretty homes in quiet, friendly, and functional neighborhoods? But will they improve the traffic? Chapter 3 concluded that existing evidence is unsatisfactory in several respects. Among the problems identified in the literature was the common absence of a conceptual framework for hypothesizing how urban form might be expected to influence travel behavior. In particular, only a small share of the studies in this area even attempt to model travel behavior in the conventional manner, that is, as travel demand. In this chapter, we develop a framework for consistently evaluating the net travel impacts of changing land-use patterns, such as many new urban designs propose. The idea is to adapt a simple model of travel demand to measurable urban form elements. This permits us to derive specific conclusions that follow directly from the assumptions of the model as well as specific hypotheses that can be tested only with data on observed behavior. These assumptions are summarized in figure 4.2. The last part of the chapter develops an empirical implementation of the model and these hypotheses, which is applied to data in chapter 5. The theory of demand provides perhaps the most straightforward way to analyze travel behavior, by emphasizing how overall resource constraints force trade-offs among available alternatives, such as travel modes and trip distances, and how the relative attractiveness of those alternatives in turn depends on relative costs, such as trip times. This framework assumes that individuals make choices, either alone or as part of a family or other group, based on their preferences over the goods in question, the relative costs of those goods, and available resources (e.g., Kreps, 1990).

An Empirical Study of Travel Behavior

The empirical strategy described here involves matching travel diary data to land-use characteristics for two different southern California regions. The first data set is from Orange County and nearby parts of suburban Los Angeles, and the other data are from San Diego. Each data set poses somewhat different opportunities and challenges in measuring the factors of interest, so we describe these in turn. The Orange County/Los Angeles travel diary data set includes data for 769 southern California residents. These were obtained from a 1993 survey administered as part of the Panel Study of Southern California Commuters. Because that survey includes each respondent’s street address, we were able to match the travel diary data to land-use variables from the 1990 census and from the Southern California Association of Governments (for the years 1990 and 1994). The travel diary covered a two-day period, and respondents were pre-assigned days, so trip making on all days of the week is represented in the data. Individual respondents were first contacted through their employer, and then for follow-up waves the same persons were contacted at home. The sample is employer based, and consequently the respondents are not a random sample of southern California residents. About half of the respondents worked at the Irvine Business Complex, a large, diversified employment center near the Orange County Airport, and the other half worked elsewhere throughout the Los Angeles metropolitan area. The descriptive statistics shown in table 5.1 illustrate how the survey oversampled Whites, highly educated persons, and persons with high income. This suggests some caution is warranted in interpreting beyond these individuals. Yet restricting attention to an educated, upper-middle-income, largely suburban population still provides interesting information, because many of the new urban designs are intended for low-density, suburban environments with demographics similar to those in this sample. The dependent variable for the model is the number of nonwork automobile trips made by an individual during the two-day travel diary period.

An Overview of Travel by Design

Start with the trips people make from home to work, and then back home again. Each commute reflects choices of where to live, where to work, when to work, when to go home, how to get from home to work, and what side trips to make along the way. Each decision depends on the opportunities available, with those in turn explained by the characteristics, resources, and values of workers, their families, their employers, other travelers, and of course the built environment of sidewalks, streets, bus routes, and rail lines connecting home to work. Nonwork trips, the great majority of trips in modern times, entail even more finely detailed mosaics of people, places, and the variety of things one obtains, or hopes to obtain, by going somewhere. Travel is the outcome of a grand confluence of human and other factors, many systematic and many others not. It will never be fully understood. But because travel poses numerous challenges, and opportunities, it would be good to understand more. Planning strategies to reduce traffic congestion and improve air quality continue to get prominent attention. Several increasingly influential efforts emphasize the potentially mitigating role of the built environment. For example, a good deal has been made in recent years of the fact that people drive less and walk more in downtown San Francisco than in suburbs anywhere. Part of this observed behavior is no doubt attributable to the kinds of people living there, people who prefer and indeed seek out the many benefits—travel and otherwise—of a diverse, high-density, mixed-use environment. But many observers have also asked, quite reasonably, if it would not make sense to design suburbs and other neighborhoods to be more like downtown San Francisco, or more like whatever it is about those places that leads people to drive less. Perhaps then people in suburbs and elsewhere would drive less and walk more. And perhaps that would lead to improvements in traffic congestion, air quality, and other transportation problems associated with the automobile.

Neighborhood Supply Issues

Chapter 3 reviewed the literature regarding the influence of the built environment on travel behavior, and chapter 4 then described one way the issue might be usefully studied. The empirical work in chapter 5 provided intriguing results while illuminating some complex issues that remain unresolved in the analysis of urban design and travel behavior. Overall, our analysis thus far suggests that the link between the built environment and travel is intimately tied to the how urban form influences the cost of travel, and that the effect of design is complex in ways not adequately appreciated in most policy discussions. Neighborhood design in particular might affect automobile travel, but we still have much to learn about the nature, generality, and policy role of any such link. That said, our analysis so far has been conventional in that it has focused on travel behavior. Yet that is only half of the story. It is also important to understand whether and how alternative land-use strategies might be more broadly implemented. Having sketched out the role of the demand for travel in understanding the impacts of urban form on trip making, we now examine the supply of urban form. Put another way, how do communities shape cities toward transportation ends? As discussed in chapter 3, a major difficulty in empirical work on travel behavior and urban design is that persons might choose residential locations based in part on how they wish to travel. Those who prefer walking are more likely to choose to live in pedestrian-friendly neighborhoods. People who prefer to commute by rail are more likely to live in transit-oriented developments. If so, then simply looking at differences in travel patterns across different neighborhoods does not give insight into how urban design causes persons to travel differently. It is possible that urban design might not lead persons to travel differently at all, at least not in the sense of changing the way they desire to travel. If there are an adequate number of communities providing less auto-dependent environments, then building more might have no influence on travel behavior.

The Trouble with Traffic

What about cars is bad? In turn, what should transportation planners do? In the early years of the automobile era, the transportation planner’s job was to develop street and highway networks. Sometimes the thinking was as simple as drawing lines on a map to connect concentrations of trip origins and trip destinations, and then building highways along the path that most closely corresponded to those lines. Air quality problems were not conclusively linked to automobile travel until the 1950s. Issues such as the displacement of persons from residential neighborhoods and the impact on habitat were secondary concerns at best until the 1960s. The primary, almost exclusive, focus during the first decades of the automobile era was to build a street and highway network that could accommodate a new mode of transportation. This began to change by the late 1960s. Planned highway networks neared completion in many cities. At the same time, the broader social costs of transportation became more apparent. Automobile emissions are a major contributor to urban air pollution. Traffic congestion has been a perpetual problem for several decades in most cities. Neighborhoods severed by highway projects often quickly deteriorated. Scholars and policy analysts now ask whether transportation resources are fairly distributed across different segments of society and how transportation access is linked to labor market success. As all of these issues have moved to the fore, transportation planning has increasingly focused on how to manage the social implications of transportation projects. Modern transportation planning now necessarily focuses as much on managing the social costs of travel as on facilitating travel. Because 87 percent of all trips in the United States in 1990 were by private vehicle (mostly cars and light trucks), the social costs of travel are, first and foremost, the social costs of the automobile. Public concerns regarding air quality, congestion, neighborhood stability, and equity gave rise to new regulatory agencies, technological innovations, and legal frameworks for transportation planning. Yet the demand for cleaner, less congested, more fair transportation systems persists. This is the context for the new urban designs. They seek, in large part, to address the social costs of automobile travel.