Transactions on the Built Environment vol 41, © 1999 WIT Press, www.witpress.com, ISSN 1743-3509 A comparison of short distance transport modes M.E. Bouwman Center for Energy and Environmental Studies IVEM University ofGroningen Nijenborgh 4 9747 AG Groningen The Netherlands Email: [email protected] Abstract This paper presents a comparison of seven transport modes in both urban and rural settings, based on four characteristics of transport modes: space use, energy use, costs and travel time. The characteristics are calculated with a computer model and based on these results the modes can be ranked. This paper shows - based on preliminary results - that the ranking order of the various transport modes based on the score on the four variables is not very sensitive to the spatial setting, although differences between spatial settings exist for the characteristics of the modes. By extending the analysis to the year 2020, slight differences occur in the ranking order of the transport modes, but no differences are found between the spatial settings. 1 Introduction Within environmental sciences, energy use and related emissions are important research topics. For transportation, combustion of fossil fuel results in the generating of e.g. CO], H?O, NO%, SOx, etc. The emission of these substances may give rise to environmental problems. Transportation has a big share in several of these emissions (Jepma [1]). In 1995, it emitted 61% of all CO in the Netherlands, 62% of the NO.,, 40% of particles and 22% of all SO:, and it had a share of 18% in energy use and CO: emissions (RIVM [2]). As transport accounts for a major share in the overall energy use and emissions, transport is a highly interesting subject for environmental research. In this paper, energy use of transport is used as an indicator of the environmental impact of transport caused by energy use and emissions. Transactions on the Built Environment vol 41, © 1999 WIT Press, www.witpress.com, ISSN 1743-3509 416 Urban Transport and the Environment for the 21st Century There is a wide variety of options for energy conservation in transport. One of the energy saving options is to switch to modes that have a relatively low energy consumption. This paper focuses on the assessment of transport modes with a minimised environmental impact per travelled kilometre. The first question arising is how to determine what mode has the smallest environmental impact, or in other words, how to rank the available transport modes according to an increasing environmental impact per travelled kilometre. Besides, it is interesting to determine whether such a ranking order changes under varying circumstances. This paper discusses whether the transport mode with the smallest environmental impact can be identified, and the sensitivity of the environmental ranking order for specific variables, such as the spatial setting. Section 2 discusses which characteristics of transport modes are relevant in determining the environmental ranking of the modes. Section 3 shows in more detail the differences between the various spatial settings, and why this subdivision is worth looking at in more detail. Section 4 discusses the method used and section 5 presents some results. 2 Transport modes For inner-city transport, a variety of transport modes is available. In general, the variety of transport modes is bigger in larger cities than in smaller ones, as public transport systems are more profitable in bigger cities. From an environmental point of view, it can be interesting to investigate whether energy savings are possible by changes in the modal split. From a variety of recent research reports (e.g. Steg [12]), one may conclude that changing the current modal split is not easy. So, before trying to influence the modal split, it is important to see which modes are environmentally preferable, and whether these modes are favourable in all situations. Next to that, it is important to see how these favourable modes score on other elements that influence travel mode choice, such as speed and costs. To discern environmentally friendly modes, two variables are introduced. The energy use of a transport mode represents much of the total environmental impact, as most of the harmful emissions are directly associated with energy use. Next to that the space use is used in the analysis. Space is also a scarce good, especially in cities. Moreover, space has a high value in densely populated areas. The space use in this analysis is used as an indicator of some of the other environmental problems associated with transport, such as noise and stench. Speed is an important transport mode characteristic. It appears that individuals have a relatively fixed time budget that they can spend on transport (e.g. Schafer [13], Hupkes [14], and Zahavi [15]). This budget comprises about one hour to one hour and a half a day. By increasing the travel speed, the individual mobility can be expanded without exceeding the travel time budget. For costs, a similar reasoning is valid. Households spend on average about 15 percent of their budget on transportation (CBS [9]). Especially for individuals with low incomes, cheaper modes might imply an expansion of their opportunities. Transactions on the Built Environment vol 41, © 1999 WIT Press, www.witpress.com, ISSN 1743-3509 Urban Transport and the Environment for the 21st Century 417 In mode choice, other variables play a role too, such as reliability, comfort and habits. These characteristics are less easy to quantify than costs and speed of modes. Therefore, costs and speed are used as indicators of the personal preferences, based on the idea that cheaper and faster modes can contribute to a higher personal mobility, which seems to be an overall goal of many individuals. Based on these considerations, an analysis will be performed on the possibility of ranking various modes, based on four variables. Two variables, space use and energy use, represent the environmental score of the modes. On a societal level, it is preferable to minimise these issues. Two other variables, costs and speed of modes, represent important characteristics of modes for an individual. In the analysis, all modes will have different scores on each of these four variables. By comparing these scores, modes can be distinguished. 3 Spatial settings The described important variables of transport vary largely among various spatial settings. Not only do patterns of mobility vary with various spatial settings; the characteristics of transport modes may also change in different circumstances. Large cities are often associated with environmentally attractive mobility patterns. This results from the fact that in a city -compared to a rural structure- more activities are possible in a smaller area, implying shorter travel distances. Greater access to public transport also makes it a better alternative compared to travelling by passenger car. This expectation is largely confirmed when looking at mobility patterns in existing situations with high and low population densities. For example, table 1 shows the modal split (km/day/person) in a very strongly urbanised (more than 2500 dwellings per square kilometre) and a rural (less than 500 dwellings per square kilometre) situation in the Netherlands in 1996. Table 1. Modal split in the Netherlands, 1996 (km/day/;lerson) Very strongly urbanised Rural Passenger car - Driver 12.15 km 37.8% 18.20 km 51.6 % Passenger car - Passenger 7.79 km 24.2% 9.66 km 27.4 % Public Transport 7.42 km 23.1% 2.90 km 8.2% Moped 0.18 km 0.6% 0.28 km 0.8% Bicycle 2.92 km 9.1% 2.66 km 7.5% Walk 1.17km 3.6 % 0.66 km 1.9 % Other 0.56 km 1.7% 0.92 km 26% Total 32.18 km 100 % 35.29 km 100 % Source: (CBS [7]) The total distance in kilometres differs about ten per cent among the two situations. Table 1 does not list the statistical data on three other situations between the two presented extremes. These intermediate situations show total distances of 34.11 km, 33.43 km, and 35.02 km respectively. This indicates that travel distances indeed vary among spatial settings, although the difference Transactions on the Built Environment vol 41, © 1999 WIT Press, www.witpress.com, ISSN 1743-3509 418 Urban Transport and the Environment for the 21st Century between very strongly urbanised settings and all other settings is bigger than the difference between two other settings. Table 1 shows a clear difference in the modal split of the two situations. In rural areas about 75 per cent of all kilometres are travelled by passenger car compared to about 60 per cent in compact cities. The difference of 15 per cent seems to be travelled on foot or with public transport in the compact city, which seems to correspond with the expectations indicated earlier. The observed mobility differences cannot be attributed fully to the differences in population density. Income is also a contributing factor for the observed differences in the modal split. The use of public transport in a compact city may be higher due to a greater access to this mode of transport. The share of public transport might also be lower in rural areas, because people who can afford to own a car prefer to live in rural areas. This second argument should correspond with clear income differences in the various situations, as it is known that car ownership levels are strongly correlated with income levels (see for example Korver [3]; CBS [10]). Table 2 gives information about different characteristics of households in various spatial settings, as well as their access to private