(Source)
Core activities are those of the highest order in the urban spatial structure, namely tertiary and quaternary activities involved in management (finance and insurance) and consumption (retailing).
Central activities are concerned by production and distribution with activities such as warehousing, manufacturing, wholesaling and transportation.
Peripheral activities are dominantly residential or servicing local needs.
Central area refers to an agglomeration of core and/or central activities within a specific location.
The emergence of a CBD (Central Business District; the central area of a city) is the result of an historical process, often occurring over several centuries (depending on the age of a city), that has changed the urban form and the location of economic activities. Obviously, each city has its own history, but it is possible to establish a general common process:
- (A) Pre industrial era. For cities that existed before the industrial revolution, the CBD was limited to small section of the city generally nearby the waterfront, the market and/or a site of religious or political importance. These were locations where major transactions took place and thus required financial, insurance, warehousing and wholesale services.
- (B) Industrial revolution. With the industrial revolution came mass production and mass consumption. This permitted the emergence of a distinct retailing and wholesaling part of the CBD while manufacturing located outside the core. Managing these expanding activities also created an increasing need for office space that located nearby traditional places of financial interaction. As the industrial revolution matured, major transportation axis spurred from the central area towards the periphery.
- (C) Contemporary era. After the Second World War, industries massively relocated away from central areas to suburban areas, leaving room to the expansion of administrative and financial activities. The CBD was thus the object of an important accumulation of financial and administrative activities, particularly in the largest cities as several corporations became multinational enterprises. These activities were even more willing to pay higher rents than retailing, thereby pushing some retail activities out of the CBD. New retailing sub-centers emerged in suburban areas because of road accessibility and because of the needs to service these new areas. Warehousing and transportation, no longer core area activities, have also relocated to new peripheral locations. The spatial structure of many cities became increasingly multi-nodal.
- Dispersed urban land development patterns have been dominant in North America over the last 50 years, where land is abundant, transportation costs were low, and where the economy became dominated by service and technology industries. Under such circumstances, it is not surprising to find that there is a strong relationship between urban density and automobile use. For many cities their built up areas have grown at a faster rate than their populations. In addition, commuting became relatively inexpensive compared with land costs, so households had an incentive to buy lower-priced housing at the urban periphery. Similar patterns can be found in many European cities, but this change is occurring at a lower pace and involving a smaller range.
- The decentralization of activities resulted in two opposite effects. First, commuting time has remained relatively stable in duration. Second, commuting increasingly tends to be longer and made by using the automobile rather than by public transit. Most transit and road systems were developed to facilitate suburb-to-city, rather than suburb-to-suburb, commuting. As a result, suburban highways are often as congested as urban highways.
Evolution of Transportation and Urban Form in North America and Europe
Both North American and European cities have been modified by similar technological changes introduced since the industrial revolution. However, a different evolution of urban form has occurred between European cities and their American counterparts, especially from the second half of the 20th century. While European cities leaned on public transit, North American cities relied more on the automobile. This evolution had a direct impact on the urban form with four important periods in the evolution of urban transportation can be identified:
- I - Walking-horsecar era (1800-1890). This era was characterized by the absence of urban mass transportation mode. People had access to locations that could be reached (walked) in less than 45 minutes (4 to 6 km). Urban densities were very high as the available space was strongly constrained by accessibility. All economic activities were concentrated in a central node along with residential areas. Reduced mobility (pedestrian area) accounts for this concentration. The horsecar made its debut in this period, which allowed the development of corridors prevailed in the following period. From the 1850s, railways enabled radial development adjacent to railway stations, especially in Europe and in older American cities (e.g. New York).
- II - Streetcar era (1890-1920). The development of the first forms of urban mass transportation lessened the accessibility constraint and enabled cities to expand along main tramway (streetcar) lines, creating corridors. In tripling the speed of urban transport, electric streetcars (public transit) expanded the spatial structure of cities. This permitted the emergence of a specialized downtown area with commercial and service activities. In Europe, tramway lines tended to expand towards long established adjacent towns, which were swallowed and integrated in the expanding city. This has allowed the development of urban activities beyond city limits. The emergence of commercial development centers along axes became apparent because more and more people, having access to trolleys, decided to relocate outside the city limits. This reinforced social stratification and favored the emergence of neighborhoods differentiated by socioeconomic status. Less fortunate people, limited in their mobility, tended to remain in central areas while the wealthier class relocated in the first suburbs. The first suburban railroads entered in service and specialized industrial districts started to take shape.
- III - Automobile era (1920-1945). Motorized transportation, mainly buses and cars, radially expanded cities, once again lessening the accessibility constraint. Never has a technical innovation had a greater impact on spatial organization than the automobile. Initially, only wealthy classes could afford their own automobiles which were used mainly recreational purposes. The private car is linked with the emergence of the firsts low density suburbs with increased ethnic and economic segregation. This went on par with the decentralization of commercial and industrial activities. It is during this phase that European and North American urban development started to diverge. In order to facilitate the diffusion of the road as a mode of urban transportation in the United States, several oil and car companies bought and dismantled tramway systems. Consequently, the influence of streetcars in the urban development in North America was being removed, while it endured in many European cities.
- IV - The highway era (1945-2000). The post World War Two era saw the large diffusion of the automobile with a growth of individual mobility. Highways favored the extension of full fledged suburbs, especially in North America. This process also took place in Europe, but to a lower extent and involved higher densities along existing transit axis. No new technologies urban transport techniques emerged during this era but improvements of transport infrastructures significantly increased accessibility. Residential and employment decentralization was thus accentuated. Also, several sub-centers emerged to serve suburbs, a process favored by the construction of ring roads around metropolitan areas. The development of new highways which circle urban perimeters have encouraged an agglomeration of commercial, distribution and manufacturing activities around high accessibility clusters in suburban areas.
The 21st century is bringing several issues about the future relationships between transportation and the urban form. In the era of telecommunications a decline in individual mobility and a concentration of activities along transport corridors can be expected, especially in North America. This process will be correlated to higher prices for individual mobility as well as attempts at substituting telecommunications to transport in several sectors of activity, notably tertiary and quaternary sectors. Future urban forms are thus likely to be of higher densities with a concentration around clusters. Yet the impacts of telecommunications on urban mobility and urban form remains to be assessed.
I hope the above section gave you a good overview of the history of urban transportation and form, and how transportation changes the spatial structure of cities.
The last point made was particularly interesting: how the information age could change the urban form. While telecommuting was hyped in the early days of the internet, it has yet to take off en masse, and the industries that have been hurt the most are the information content creation industries (i.e. News Paper, music). I don't know if or how the internet will change our urban form, but it's probably worth investigating further.
Also, while this shows (in historical context) how transportation changes urban form, it doesn't quite explain what drove the change in transportation besides new technologies.
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