A Cycle of Dependence: Automobiles, Accessibility, and the Evolution of the Transportation and Retail Hierarchies

This paper explores how the automobile has indirectly led to dramatic changes in patterns of accessibility to retail and service activity within metropolitan regions. The automobile instigated a greater articulation of the hierarchy of transportation facilities, as reflected in a greater differentiation between the local and the regional systems. At the same time, the automobile instigated a collapse in the retail hierarchy, by encouraging the growth of community and regional centers at the expense of local shops and the central business district. The result has been a cycle of dependence, in which suburban communities are designed for the automobile, leaving residents little choice but to drive. Access to retail activity is now dependent on the automobile but vulnerable to increasing levels of congestion that are driven by dependence on the automobile. Accessibility has been defined as the "intensity of possibility of interaction" (Hansen 1959). The accessibility of a particular location is determined by the distribution of potential destinations around that location and reflects both the ease with which each destination can be reached and the magnitude, quality, and character of the activity found there. Choice is central to this definition: the greater the number and variety of potential destinations, the greater the choice that residents have and the higher the level of accessibility. Travel cost is also central to this definition: the lower the travel costs, both time and monetary costs, the greater the number of destinations that can be reached within a set fiscal or time constraint and the higher the level of accessibility. The most dramatic change in accessibility in metropolitan regions in this century can be attributed to the automobile, which directly expanded accessibility by reducing the travel time to all destinations and providing residents with unprecedented freedom to choose when and to where they traveled. Less obviously but perhaps more importantly, the automobile indirectly led to dramatic changes in patterns of accessibility to retail and service activity within metropolitan regions by instigating significant changes in the transportation and retailing systems. In general, the articulation of the hierarchy of transportation facilities has increased, with greater differentiation between the local and the regional systems. At the same time, the retailing hierarchy has collapsed, due to the growing importance of medium-sized and specialized centers. As a result, access to regional centers of activity has improved, through the development of urban expressway and freeway systems and the rise of regional shopping centers. On the other hand, access to activity in the local area has declined, because of planning and design practices that separate land uses and emphasize automobile travel, coupled with an increase in the scale of "neighborhood" centers and establishments. These changes have very direct implications for travel, as well as for quality of life. Prior to the wide-spread adoption of the automobile, a suburban resident would walk to local stores to buy the sorts of goods and services she needed on a regular basis. For less frequently purchased goods, she would ride the streetcar to downtown to shop in department stores and specialty shops. Now residents drive to one of the nearby strip malls to do their grocery shopping or pick up a prescription, or drive to one of several regional malls in the area to buy clothes and household goods. Today's typical suburban resident does not have the option of walking to a local store, either because there is no store within walking distance, or the walk is too dangerous and unpleasant. The resident has no reason to shop in the central business district, because the mall is much closer, has convenient parking, and offers all of the same goods and services. Whether the new accessibility patterns are an improvement is to some extent a matter of preference: for those who like to walk, it might be worse; for those who like shopping malls, it is undoubtedly better. The problem is that these accessibility patterns are not sustainable. Because they were designed for automobile useÑsolely designed for automobile use, in most casesÑand are dependent on high-speed travel, not proximity, these patterns generate levels of automobile travel that often exceed the capacity of the transportation system, creating congestion. As congestion increases, accessibility declines, all else equal, since accessibility is partly determined by travel time: if congestion increases, then speeds decrease, and destinations are farther away from the perspective of travel time. The accessibility patterns that have emerged are particularly vulnerable to increasing congestion, because they are dependent on access by automobile, but for the same reason the patterns have led to increasing congestion. In other words, it is a self-destructive cycle of dependence. This paper traces the role of the automobile in instigating these changes, describing first the emergence of the concept of a hierarchy of streets and highways, and then the upheaval in the retail hierarchy. In both cases it is clear that, as a result of these changes, accessibility to commercial areas has become dependent on the automobile. This paper concludes by discussing how this dependence has both increased congestion and left accessibility vulnerable to increasing levels of congestion. The question that remains to be answered is whether this cycle of dependence will continue indefinitely or be broken before accessibility declines significantly. The Transportation Hierarchy Although the basic rectilinear grid found in suburban communities remained generally unchanged until after World War II, the ideals that initiated the change emerged many decades earlier. The Garden City movement at the end of the 19th Century led to a "rediscovery" of the street system as a crucial design element and instigated a movement away from the grid toward a new pattern and scale of streets that would improve safety and increase light, air, and the sense of nature in suburban communities (Wolfe 1987). However, it was the increase in automobile traffic in the 1920s that eventually resulted in the emergence of the curvilinear streets concept and cul-de-sacs structured into a hierarchy of streets scaled according to their use. The hierarchy concept was popularized by Raymond Unwin, Frederick Law Olmsted Jr., and Clarence Perry, among others. It achieved its fullest definition in Clarence Stein and Henry Wright's "landmark" design for Radburn, N.J., in 1928, in which the rectilinear grid "was unequivocally rejected" (Kostof 1991: 80). In their plan, houses were clustered on cul-de-sacs that linked to distributor streets that, in turn, linked to the arterial streets that bounded the development. In addition, pedestrian traffic was almost completely segregated from automobile traffic. A central open space contained "serpentine pedestrian and bicycle paths diving under rusticated over-bridges" (Hall 1988: 127) so that residents could walk from one end of the community to the other without having to cross a single street (Figure 1). The combination of the clustering of housing, the shift away from the grid, and the creation of a "superblock" meant that "not only through traffic, but all traffic, was excluded" from much of the development (Hall 1988: 127). Stein called their plan for Radburn "a town for the motor age" (Kostof 1991: 80): it guaranteed residents the benefits of the automobile but minimized its negative impacts, particularly with respect to pedestrian safety. Concerns over safety due to rapidly increasing automobile traffic soon led to the establishment of formal guidelines and policies on the creation of hierarchies of streets. In 1938, the Federal Housing Administration published two pamphlets, "Planning Profitable Neighborhoods" and "Successful Subdivisions," which defined construc-