Density planning and public transport
In lower density cities, many destinations demand a long distance journey, as a result it costs a large amount of energy and reduces urban efficiency, especially in car dominated cities. Generally if urban densities are low, but the corridors are high, they still can build a good transit system, such as most European cities. However if low densities are the main characteristics of cities, they are likely to be based around cars, as people need to achieve their destination in their reasonable time. In attention, public transport in low density cities may be inactive, because the use of it also needs to be justified by the population. If there are no enough people live in these cities, the timely services of public transport cannot be competitive, as the denser the places served, the more viable they become (Newman and Kenworthy, 2006).
Density is a useful tool to city planners to consider about the transit building, as the resulting Transit Oriented Development (TOD) are the affordable housing strategy for residents to save their income. In the US, Ewing, Bartholomew, Winkelman, Walters and Chen (2007) demonstrate that about 60 percent of new growth to compact patterns can reduce CO2 emissions by 85 percent metric tons annually by 2030. Some critics argue that there is no connection between TOD and density planning. While density planning would be a more available way to improve TOD, as through the density planning it can reduce car use per capita among its residents by saving approximately 20 percent of their income (Cervero, 2008).
Raising density is the priority in many low density cities, aiming to reduce the automobiles use to decline the concentrations of GHG. It is appears that growing inner city is an appropriate method to raise city density. There is a problem that it is difficult to define inner city. According to the research of Newman and Kenworthy (1999) “The inner city is the area mostly developed before automobiles-dependent town planning”. It is opposite to suburbs. In the US, these areas often represent the old areas, such as the City of New York. In terms of the relationship of automobiles and population, in order to reduce car use it is reasonable to have job densities similar in population density roughly. It is found that there is a comparison between US inner cities and European inner cities. In Europe, the two are more or less equal, while in the US, the job density is lower than population density significantly in 24 percent (Clark, 1982). This evidence reflects that more people are willing to take employments in the suburbs, and it is the reason why the car use cannot be reduced. The increase of job density can drive the transfer of population density essentially. Currently, increasing number of low density cities plan to raise their inner densities to drive population in inner areas. For example, in Sydney, its inner areas grew 15 percent, the middle suburbs grew 12 percent and outer suburbs grew 7 percent from 2001 to 2011 (Newman and Kenworthy, 2011). This is also the reason why increasing number of young people want to live in urban areas. With this evidence, whether the job density or population density, they have been greatly improved in urban areas. The study of Newman and Kenworthy (1999) shows that with the increase of the urban density (persons/ha), the per capita private passenger transport energy use can decline (figure 1). As the journey distance of residents would be influenced by the density planning. The data shows that the length of journey to work is closely link to the density of a city. For instance, the low density cities in US average 15.0 kilometers; the medium density cities in Europe average 10.0 kilometers; and the high density cities of Asia average 7.9 kilometers (Newman and Kenworthy, 1999). There is an issue to be discussed how to replace automobile under density planning. As a discussed in the transport patterns, density planning should be paid more attention, because it can impact the distance to work and income of residents.
Cervero, R. 2008. Effects of TOD on Housing, Parking and Travel, TCRP Report No.128, Federal Transit Administration, Washington, DC.
Clark, C. 1982. Regional and urban location. University of Queensland Press, St Lucia, Brisbane, Australia.
Ewing, R. H., Bartholomew, K., Winkelman, S., Walters, J. and Chen, D. 2007. Growing Cooler: The Evidence on Urban Development and Climate Change, Urban Land Institute, Washington, DC.
Newman, P. and Kenworthy, J. 1999. Sustainability and Cities: Overcoming Automobile Dependence, Island Press, Washington, DC.
Newman, P. and Kenworthy, J. R. 2006. ‘Urban design and automobile dependence: How much development will make urban centers viable’, Opolis 2(1): 35-52.
Newman, P. and Kenworthy, J. 2011. ‘Peak car use: Understanding the demise of automobile dependence’, World Transport Policy and Practice 17(2): 32-42.
Figure 1. Newman, P. and Kenworthy, J. 1999. Sustainability and Cities: Overcoming Automobile Dependence, Island Press, Washington, DC.