Transportation and Urban Planning
Description of a research program at Aalborg University.
By Professor Petter Næss, Aalborg University, Department of Development and Planning.
Revised February 9, 1999
Introduction......
Distances, accessibility and needs......
Status of knowledge regarding the influence of some urban form variables on traveling distances, modal split and energy use.
Density......
Location of residential areas......
Location of workplaces......
Geometrical shape......
Regional development pattern......
Public transport, road system and parking possibilities......
The resources, values and preferences of the travelers......
The lifestyle concept......
Research issues given priority within the program “Transportation and Urban Planning”......
Methodological considerations......
Data sources......
Geographical areas of investigation......
Study of the regional pattern of development......
Study of lifestyle domains and transportation......
Personnel and work schedule......
Reference group......
Cooperation with other research projects......
References......
Transportation and Urban Planning
Description of a research program at Aalborg University.
By Professor Petter Næss, Aalborg University, Department of Development and Planning.
Revised February 9, 1999
Introduction
The theme of the research program “Transportation and Urban Planning” is how physical planning can be used to influence the extent and character of transportation, and thus also energy use for transportation. Combustion of oil, coal and gas causes pollution, which both damages people’s health and the natural environment, and which is probably in the process of bringing the global climate out of balance. Therefore, it is an important goal for environmental protection to limit, and preferably reduce, the energy use in the society. A high extent of transportation also implies a number of other environmental disadvantages, such as traffic accidents, noise and the encroachments of previously unbuilt areas or existing buildings represented by the traffic installations themselves.
By physical planning, we primarily mean planning according to the Danish Act on Planning (Lov om planlægning), particularly preparation of the main structure of the municipality plan with division into country zone and urban zone, and preparation of local plans and regional plans. The program does not aim to evaluate the effectiveness of such planning regarding its actual ability to control land use and building activity. Instead, focus is directed towards the way in which we use land and localize and shape developmental areas, takes part in determining how extensive the transportation will be, with what conveyances it will be made, and how much energy it will require. The program concentrates on transportation of people. This implies that the influence of urban planning factors on freight will not be discussed.
There is a mutual influence between land use and transportation. Changes in land use may cause changes in transportation activity. Such changes may accomplish that it may be considered desirable or necessary to change the transportation system. Land use changes may also influence the transportation system directly, for instance in the form of investments in roads and public transport connections to planned development areas. Changes in the transportation system may, on the other hand, accomplish land use changes, for instance by changing the balance between the attractiveness of different conveyances, or by making it less time consuming to make longer journeys. In addition, changes in the transportation activity may influence land use directly, for instance because reduced travel activity due to considerable increase in fuel prices makes the outskirts less attractive as development areas.
These mutual interactions between land use and transportation is shown schematically in Figure 1. Of the different lines of influence shown in the figure, the program primarily concentrates on one, namely the influence of land use on transportation activity. To some degree, however, the influence of the transportation system on the transport activity will also be investigated.
The geographical distribution and structure of the building stock (the pattern of development), the mutual location of different functions (the location pattern) and the design of the transportation system make important conditions for the extent of transport, the distribution between different conveyances and the energy use for transportation. Yet it cannot be concluded, for instance from the shape and location of a home, how much energy for transportation is actually being used by the inhabitants of this particular building. Very much also depends on the inhabitants’ characteristics, for instance their professional activity, whether there are children in the household, the location of workplaces and relevant schools and shops, and last, but not least, what kind of lifestyle and habits the inhabitants have.
Figure 1 Relations between changes in transportation system, transportation activity and land use. Adapted from Needham (1977:134)
A basic hypothesis within most research on relations between physical/functional urban structure and transportation is that the material structure in an urban area forms a set of incentives, influencing on people’s transportation activity. It is presumed that people will try to reach their daily activities with the least possible inconvenience. The inconvenience may include economical expenses, time use and other sorts of efforts. As a measure for a person’s total inconveniences by doing a journey, transportation economists have introduced the concept of generalized travel costs. The shorter distance to the destination, and the faster, cheaper and more comfortable means of transportation available, the lower are the generalized travel costs for reaching the destination, and the higher is the accessibility. In addition to the accessibility, the journeys to a locality of course also depend on the reasons people have for going there. Here, factors like the number of and the variety of workplaces and service functions, or the number of inhabitants, will influence the number of travels attracted by a certain locality.
In practice, also a number of factors other than the generalized travel cost influence people’s transportation activity. These factors include both personal conditions (like for instance age, sex, income etc.) as well as people’s standards of value, norms, life style and acquaintances. Human action is influenced by both structural limitations and incentives (of which the material urban structure makes up only one of several categories), and by the individuals’ resources, preferences and wishes. It is not the development structure and the location pattern in themselves that generate transportation, but people living and working in specific places, visiting different destinations or transporting goods. The resulting transportation pattern is dependent on people’s resources, needs and wishes, modified through the limitations and the possibilities caused by the structural conditions of the society (see Figure 2).
The importance of the influence from the physical/structural conditions, as compared to the influence from individual characteristics, on the transportation activity, will be further discussed in the section on methodological considerations later in the paper.
Primarily, it is the local/regional transportation that can be influenced on through physical planning. Altogether, journeys shorter than 30 kilometers represent about half of the total amount of transportation in Norway, measured in kilometers (Rideng 1994). A somewhat older Danish study quotes that 70 percent of the passenger transportation in Denmark consist of journeys shorter than 40 kilometers (Larsen et al 1982b). Transportation over long distances, for instance holiday trips or freight between different parts of the country, is not likely to be much influenced through physical planning[1].
Reduced energy use for transportation may be achieved in three basic ways:
- By reducing the movement of people and goods.
- By transfer from energy demanding to more energy efficient means of transportation (for instance from private cars to public transport)
- By making the different means of transportation more energy efficient (through improved vehicle technology, a higher capacity utilization, better traffic flow, a “softer” way of driving etc.).
Land use and settlement planning may particularly contribute to reducing the energy use of transportation in the two first mentioned of these three ways, but also the possibilities of high capacity utilization in the public transport may be influenced on. Furthermore, changes in transportation infrastructure (road building or changes in the supply of public transport) may influence the energy efficiency of the different means of transportation as well as on the distribution of travelers on different conveyances. This research program primarily concentrates on how the development and location pattern influence the extent of transportation and the modal split between different conveyances. The importance of the provision of public transport and the design of the local road and path system will also be discussed.
Figure 2. Transportation activity as a function of urban planning factors, as well as individual characteristics of the travelers.
Distances, accessibility and needs
Theoretically, it can easily be shown that it is possible for the inhabitants of densely populated towns to reach their daily tasks with less transportation that what is necessary in towns with scattered, low density development patterns. In Figure 3, the relation between density and average distance between functions is symbolized by dots within circles of different sizes. All three circles contain the same number of dots. We immediately see that the average distance between the dots is shorter in circle b) than in circle a), where the density of dots is lower. It can also easily be seen that the average distance between the dots is further reduced in circle c), where a larger part of the dots is concentrated towards the center.
Figure 3 Relation between density and average distance between functions, symbolized by dots within circles of different sizes. From Næss (1997).
But as we know, people are not dots. Even if the average distance between different functions like homes, workplaces and service facilities is shorter in dense and concentrated towns, this does not necessarily mean that the transportation actually taking place, is less. With increased accessibility, new needs are generated. The increased accessibility provided by the density and the concentration may therefore be utilized to choose between a broader range of workplaces, shops and dwellings, rather than to reduce the amount of transportation.
The research carried out in this field up to now, however, indicates that even though some of the benefits gained by short distances is “consumed” this way, dense and concentrated towns do contribute to lower energy use for transportation, than towns with a low density, fragmented development pattern. The urban form factors that primarily seem to influence the extent of transportation, the modal split and the energy use for transportation, are density, location of dwellings, location of workplaces, geometrical urban form, regional development pattern and the structure of the transportation system. It is, however, uncertain how great importance each of these factors has in different geographical, social and cultural contexts. For example, it is reasonable to presume that the importance of living or working near the town center will not be the same in a small country town as in a large city. Nor is it sure that the population density will be equally important in large and small towns. Further, there are limitations regarding the extent to which experiences from investigations abroad can be transferred to Danish conditions.
In addition, there is still some uncertainty related to some of the results from the research in this field so far. Among other things, this applies to the transportation energy data in the studies where the energy use is calculated from information about fuel sales within specific geographical areas (see below). It is also desirable to have a closer look into how lifestyle factors affect people’s travel pattern in interplay with urban form and socioeconomic characteristics. Some debaters have hypothesized that the values and attitudes of the inhabitants of different parts of a town, for instance regarding car use, may be different, creating a possible source of error in the research carried out till now.
Another important question arising is whether a modest extent of local transportation will result in extended transportation in other places, as long as the total purchasing power does not change. Is it so – given a certain level of income – that “the sum of vices is constant”, and that households managing on a small everyday transportation consumption, create even heavier environmental strain through for instance week-end trips to a cottage or long-distance holiday trips by plane? In the professional debate, some parties have claimed that people living in high-density, inner-city areas, to a larger extent than their low-density counterparts, will seek out of town in the weekends, for instance to cottages etc., in order to compensate the lack of access to a private garden. In addition to this “hypothesis of compensation” others, including the Swedish mobility researcher Bertil Vilhelmson (1990), have launched a “hypothesis of opportunity” implying that the time and money people save due to shorter distances to daily destinations, probably will be utilized by increasing the length of their leisure journeys. Thus, it will be interesting to examine to which degree the effect of living close to the daily destinations is neutralized by longer, more energy demanding leisure journeys among those who have a short distance to the most regularly visited functions.
As mentioned earlier, our basic hypothesis is that travel is influenced by both spatial/structural conditions and by the actors’ individual resources, values and preferences. Consequently, the research design must take into consideration structural conditions as well as individual characteristics of the actors. It is, however, not sufficient to discover how traveling patterns vary between residential areas differing in location and physical structure as well as in their composition of lifestyle groups. If the results of the project are to be useful within physical planning, we have to clarify whether any differences in the traveling patterns of the examined residential areas are caused by their physical and locational characteristics, by the socioeconomic and lifestyle characteristics of their inhabitants, or by both. If the differences in transportation turn out to be mainly a result of differences in socioeconomic status, values and attitudes, the results of the project can only to a small degree be used to give recommendations about principles for an energy-conscious urban planning, as it is beyond the reach of physical planning to change people’s socioeconomic resources, values and attitudes. If, on the other hand, clear differences are found between the traveling patterns of residents living in different urban situations, also when controlling for variation in socioeconomic status and other lifestyle factors, the results may have important implications for a physical planning aiming to confine car traffic and energy use for transportation. Consequently, we must try to identify the separate influence of each potential explanatory factor.
Status of knowledge regarding the influence of some urban form variables on traveling distances, modal split and energy use.
Below, we will give a short overview of what we have reason to believe today about how the traveling distances, the modal split and the energy use for transportation are influenced by a number of urban planning factors. In a later section, we will discuss some central concepts and theories that may be used when investigating how individual lifestyle factors influence travel.
Density
As we have already seen from the example with dots within circles of different sizes, a high population density implies shorter average distances between dwellings, workplaces and service functions. The average mutual distance between the dwellings is also reduced when the overall density of the town increases, contributing to shorter traveling distances for visiting relatives and friends within the town.
A high density also facilitates more frequent departures and shorter distances to public transport stops. In dense urban areas, there are also usually narrower streets and more shortage on parking places than in less dense areas. Consequently, high density contributes to shorter traveling distances as well as a more extensive use of public and non-motorized means of transport. Both contribute to reduction of the energy use for transportation.
By population density, we here refer to the density of inhabitants within the urban settlement, and not for instance within the administrative territory of the municipality, which may include both urban settlements and large unbuilt or sparsely populated areas.
Investigations in Nordic towns show a clear relationship between density and energy use per capita for transportation. (Næss 1993, 1995a, b; Næss, Sandberg og Røe 1996). This also holds true when controlling for other factors influencing on the energy use, for instance income, car ownership and commuting to and from exurban areas. Keeping constant such factors, the energy use per capita is about 25 percent higher in the least dense than in the densest of the examined cities. These results point in the same direction as Newman and Kenworthy’s (1989a, b) much referred examination of urban structure and energy use for transportation in 32 cities at a worldwide scale. The last mentioned examination however, did only to a small degree control for the influence from socioeconomic factors, although the cities varied strongly in their social, economic, cultural and political conditions[2]. A clear connection between density and transportation pattern has also been found in a recent investigation of different towns within the Paris region (Fouchier 1998). Distinct from this, a comparison of transportation pattern in different “functional urban regions” in Great Britain shows little or no connection between density and transportation (Gorden 1997). It is, however, not clear how the density of these regions was measured in Gordon’s examination, for instance whether continuous, unbuilt areas were also included in the basis of calculation.
In the above mentioned examination of Nordic towns, the energy use was measured by registering the retail sale of gasoline and auto diesel within the boundaries of the urban area of each town, combined with information about the fuel and electricity consumption of the local public transport. As mentioned above, certain sources of error are associated with using data for fuel retail sale within the boundaries of the densely populated area as an indicator of the inhabitants’ consumption of fuel for local transportation[3].