© Association for European Transport and contributors 2009 1 USING TRANSPORT MODELS IN SPATIAL PLANNING: ISSUES FROM A REVIEW OF THE LONDON LAND-USE/TRANSPORT INTERACTION (LUTI) MODEL Alan Wenban-Smith Urban & Regional Policy Tom van Vuren Mott Macdonald 1. INTRODUCTION 1.1 Context Major transport investments are generally made in order to achieve wider economic, social or environmental purposes 1 . A problem this sets for transport modelling is that a worthwhile transport investment will necessarily change the pattern of economic and social activity that the transport system serves, and therefore the pattern of transport demand, generally leading to more travel. The conversion of improved accessibility into other forms of benefit thus means that traffic forecasts made by ‘pure’ transport models decline in accuracy over time. While such models may have land-use inputs, in the form of independently predicted patterns of physical development (usually policy-driven), this is not the same as accommodating the changes in patterns of activity that result from the transport changes themselves. An authoritative investigation of the link between transport and the economy in the UK found that “.. in general, the value of direct transport benefits must decline if indirect economic benefits are to grow”. 2 However, since in a perfect market the value of the ultimate economic benefit arising from changed patterns of location is equal to the value of the initial time savings, regardless of long and tortuous the processes in between, this problem has not until recently received the attention it perhaps deserves. In recent years there has been an increasing interest in indirect and longer- term economic and social effects arising from imperfect markets – notably the economic benefits of urban agglomeration and the increasing social concerns about urban decline. The ‘new economic geography’ 3 offers perspectives on how transport improvements interact with the social and economic processes concerned by changing the pattern of locational choices. Because of this, it is becoming increasingly untenable for major infrastructure projects to rely on modelling approaches that ignore these interactions, or rely on initial transport benefits as the main means of testing value for money. Where the justification of a project depends on strategic effects beyond the transport system and in the longer term, the broader approach offered by LUTI modelling is now seen as a way forward. However, the processes involved are complex and techniques are still developing. In this paper we explore the implications for planning systems as well as modelling techniques. 1.2 London LUTI model (LonLUTI) and Thames Gateway Bridge (TGB) Transport for London (TfL) commissioned David Simmonds Consultancy (DSC) to develop a London LUTI model (LonLUTI) to provide the top strategic level of transport analysis supporting London’s spatial planning work 4 . The