Source: adapted from Muller, P.O. (1995) "Transportation and Urban Form: Stages in the Spatial Evolution of the American Metropolis". In Hanson, S. (ed.) The Geography of Urban Transportation, 2nd Edition, New York: Guilford, p. 29.

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. For instance, in 1938 General Motors and Standard oil bought the Pacific Electric Railway of Los Angeles, dismantled it and replaced tramways with buses. 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.