The Spatial Constraints of Urban Transportation

The amount of urban land allocated to transportation is often correlated with the level of mobility. In the pre-automobile era, about 10% of the urban land was devoted to transportation, which was simply roads for dominantly pedestrian traffic. As the mobility of people and freight increased, a growing share of urban areas was allocated to transport and the infrastructures supporting it. Large variations in the spatial imprint of urban transportation are observed between different cities as well as between different parts of a city, such as between central and peripheral areas. The major components of the spatial imprint of urban transportation are:

·         Pedestrian areas. Refer to the amount of space devoted to walking. This space is often shared with roads as sidewalks may use between 10% and 20% of a road’s right of way. In central areas, pedestrian areas tend to use a greater share of the right of way, and in some instances, whole areas are reserved for pedestrians. However, in a motorized context, most pedestrian areas are for servicing people’s access to transport modes such as parked automobiles.

·         Roads and parking areas. Refer to the amount of space devoted to road transportation, which has two states of activity; moving or parked. In a motorized city, on average 30% of the surface is devoted to roads while another 20% is required for off-street parking. This implies for each car about two off-street, and two on-street parking spaces are available. In North American cities, roads and parking lots account for between 30 and 60% of the total surface.

·         Cycling areas. In a disorganized form, cycling simply shares access to pedestrian and road space. However, many attempts have been made to create spaces specifically for bicycles in urban areas, with reserved lanes and parking facilities. The Netherlands has been particularly proactive over this issue with biking paths and parking areas active component of the urban transport system; 27% of the total amount of commuting is accounted for by cycling.

·         Transit systems. Many transit systems, such as buses and tramways, share road space with automobiles, which often impairs their respective efficiency. Attempts to mitigate congestion have resulted in the creation of road lanes reserved for buses either on a permanent or temporary (during rush hour) basis. Other transport systems such as subways and rail have their own infrastructures and, consequently, their own rights of way.

·         Transport terminals. Refer to the amount of space devoted to terminal facilities such as ports, airports, transit stations, railyards, and distribution centers. Globalization has increased the mobility of people and freight, both in relative and absolute terms, and consequently the amount of urban space required to support those activities. Many major terminals are located in the peripheral areas of cities, which are the only locations where sufficient amounts of land are available.

The spatial importance of each transport mode varies according to a number of factors, density being the most important. Further, each transport mode has unique performance and space consumption characteristics. The most relevant example is the automobile. It requires space to move around (roads), but it also spends 98% of its existence stationary in a parking space. Consequently, a significant amount of urban space must be allocated to accommodate the automobile, especially when it does not move and is thus economically and socially useless. In large urban agglomerations, close to all the available street parking space in areas of average density and above is occupied throughout the day. At an aggregate level, measures reveal a significant spatial imprint of road transportation among developed countries. In the United States, more land is thus used by the automobile than for housing. In Western Europe, roads account for between 15% and 20% of the urban surface, while for developing economies, this figure is about 10% but rising fast due to motorization.