Relationships between transport emissions and travel patterns in Britain
Introduction
Increasing numbers of environmental indicators are being monitored by a variety of agencies at the local, regional, national and international level. In transport policy, environmental indicators are becoming more important in the assessment of current local transport policies and programmes and in the development of future policies and programmes. Because of the limited data and resources available for monitoring, it is crucial that the environmental indicators, which are collected and monitored, are representative of environmental impacts, widely available, inexpensive and easy to collect.
This paper explores the relationship between transport emissions and various measures of passenger travel patterns in Britain. It examines the usefulness of various measures of travel patterns as environmental indicators of vehicle emissions and energy use. If certain measures of travel patterns were reasonable proxies for vehicle emissions and energy use, and could be collected relatively easily without complex measurement or calculation, they would be useful for environmental monitoring and the assessment and development of transport policy.
In order to examine the similarities of various measures of travel patterns with vehicle emissions and energy use, the paper uses original data from the 1989/91 National Travel Survey (one of the most recent sets of raw data available for analysis). The method developed in this paper identifies how a range of vehicle operating conditions can be incorporated into calculations of vehicle emissions and energy consumption using data from the National Travel Surveys.
The paper is divided into four main sections. The first section of the paper identifies the main emissions from transport, their impacts and recent trends. The second section discusses the way in which various operating conditions affect transport emissions and energy consumption. The third section identifies how vehicle emissions and energy consumption can be calculated to take these operating conditions into account. In the fourth section of the paper, per capita energy consumption and vehicle emission figures are compared using correlation analysis to examine the extent to which travel patterns follow similar trends. The paper shows that certain measures of travel patterns such as travel distance are reasonable proxies for vehicle energy consumption and emissions of most pollutants. These measures are therefore potentially useful environmental indicators for transport.
Section snippets
Transport emissions—impacts and trends
Transport produces a number of emissions and a range of environmental impacts. Emissions include global pollutants (such as carbon dioxide which contributes to global warming), national or regional pollutants (nitrogen oxides which produces acidification or ‘acid rain’ for example) and local pollutants (such as particulates which contribute to respiratory problems including the increased susceptibility to asthma). Transport's contribution to environmental pollution in urban areas is
The effects of vehicle operating conditions on emissions and energy consumption
Potter reports only a small improvement (5%) in the energy efficiency of new vehicles between 1970 and 1993. This corresponds with analysis of vehicle efficiency by Sorrell (1992), who reports that the average fuel consumption of new cars decreased through the 1970s until the late 1980s and then increased slightly until 1990. This is partly the consequence of trends towards more powerful and heavier cars which have mitigated against some of the fuel and emission reductions brought about by
Calculation of vehicle emissions and energy consumption
This section describes how vehicle emissions and transport energy consumption was calculated from the 1989/91 National Travel Survey (Department of Transport, 1995) to take into account the effect of the various operating conditions identified above. The method is similar to the one used by Anable et al. (1997) in calculating travel emission profiles for rural areas.
Comparing vehicle emissions, energy consumption and travel patterns
Having calculated energy consumption and vehicle emission figures for each journey, aggregated figures of energy consumption and emissions per person were calculated. These aggregate figures were then compared using correlation analysis in order to examine the extent to which they follow similar trends. The energy consumption and vehicle emission were then aggregated again to give average figures per person in each survey area. The figures were compared with various measures of travel patterns
Conclusions
This paper has explored the relationship between transport emissions and the relationship between various measures of travel patterns. It has examined whether the travel patterns within an area can be used to represent trends in vehicle emissions using data from the 1989/91 National Travel Survey. The paper has identified the main emissions from transport, their impacts and recent trends. It has identified the way in which vehicle operating conditions affect emissions and energy consumption and
Acknowledgements
The author wishes to thank David Banister (University College London) and Stephen Potter (Open University) for their constructive and encouraging comments on this paper. The author also wishes to acknowledge the research studentship from the Engineering and Physical Sciences Research Council, which made this study possible.
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