The assessment of transport impacts on land use: practical uses in strategic planning

Abstract

This article, focusing upon the UK, examines the relevance to strategic planning of methods to estimate the impacts of transport policy on land use processes. The study applied three differing techniques for forecasting these impacts to a common study area, and assessed planners’ views on each. The methods comprised a Delphi survey, a simple static land use model, and a linked land-use/transport model. It was found that many factors influenced planners’ views on appropriate methods. In general, comprehensive-modelling methods could provide a tool suitable for the needs of planners, but only if the underpinnings of the model were clear.

Introduction

Within the UK at present there is considerable interest among planners in integrating land use and transport planning, primarily to assist in reducing car based travel, and hence obtaining sustainable development patterns. As a result, the examination of land use and transport interaction has focused almost entirely on how land use patterns affect travel demand, and which urban forms are most energy efficient (e.g. Department of the Environment and Department of Transport, 1993, Hall, 1997, Coombe and Simmonds, 1997).

The converse, i.e. how transport in turn affects urban development, has received only cursory interest, and is only briefly mentioned in the UK Government's current (but due to be revised) advice on land use and transport planning, Planning Policy Guidance 13 (Department of Environment and Department of Transport, 1994), or in the recent White Paper (Department of the Environment, Transport and Regions, 1998). Yet there are strong reasons to support the view that these impacts should be studied; from the clear long term link between transport technology and urban form (Hall, 1989, Giannopoulos and Curdes, 1992), through micro level studies regarding complex transport influences on development, to theoretical arguments regarding urban dynamics over time (e.g. Hunt and Simmonds, 1993, Mackett, 1995). It is the methods to assess how transport can influence land-use which are the focus of this paper.

There is no history within the UK planning of consistently examining the impact of transport on land use. Previous research (Still, 1996), has found that these impacts remained external to the mainstream planning practice because:

• there is no requirement in policy to examine such impacts;

• there is a perception that unplanned development impacts resulting from transport can be controlled via the development planning process;

• there is a belief that the circumstances under which development can be directly attributed to transport changes are vague and difficult to predict;

• there is a widespread unfamiliarity with the methods to forecast impacts.

Comparative research in the USA has found that, in contrast to the UK, there is overt recognition of the importance of transport impacts on land use patterns, and hence on patterns of travel demand (Still, 1996). There are legislative requirements to examine these impacts for US urban areas failing to meet air quality regulations. Planners must show (through forecasting) that their transport policies will not worsen air quality through any mechanism, including land use response.

However, in common with the UK, in the USA there is still a debate over the most appropriate method to examine these impacts. This research therefore assesses the relative merits of different methods for the practical examination of transport impacts on land use. A wholly analytical assessment of the range of methods would be difficult to achieve. Instead the criteria for assessment is based upon experience in using a variety of methods to consider a set of common policy tests in a common study area, and practising planners’ own assessments of the methods and the results.

This paper begins by describing three methods selected from the range of possible techniques. An assessment is made of the methods based upon the criteria of (1) the validity of the method, and (2) the plausibility of the resulting forecasts. The remainder of the paper then focuses upon planners’ reactions to the methods and the results. The planners were asked to make an assessment against a similar set of criteria, namely their views on: (1) the relevance of the outputs; (2) the validity of the methods; (3) the plausibility of the forecasts; and (4) the overall importance of the methods to strategic planning practice. Conclusions are drawn from these findings concerning the criteria necessary for a method to satisfy the planners’ requirements.