The development of the TIGRIS XL model: a bottom-up approach to transport, land-use and the economy

The project appraisal method in the Netherlands distinguishes direct effects, indirect distribution effects and indirect generative effects. In general transport models are available for calculating the benefits of transport projects to travellers as part of the direct effects. The TIGRIS XL model, a Land-Use and Transport Interaction model, adds indirect distribution effects for the housing and labour market, by modelling changes in the spatial distribution of jobs and residents. This paper describes the current TIGRIS XL model and how it can be applied in the evaluation of transport projects. It also discusses ideas on how to extend the TIGRIS XL model to address indirect generative effects as well. The current TIGRIS XL model, its integration with the National Model System (standard tool for the Dutch government to analyze the effects on passenger transport) and basic design principles are the starting point of such an exploration. These design principles include: • an emphasis on detail, both spatial as well as in socio-economic segments, to account for differences in the availability of choice alternatives and in choice behaviour, and to provide impacts by region and socio-economic group; • the requirement that the relationships used rest on an empirical foundation. In this paper a post-processing module is proposed, which transforms changes in travel times and land-use into agglomeration effects. The so-called agglomeration effects combine several of the generative effects; like scale advantages, increasing variety of products, labour market matches and knowledge spill-over. The effects on productivity of changes in the agglomeration indicator can be estimated on existing data sources as is demonstrated in the UK (Graham 2005). Paper prepared for the conference on “Economics impacts of changing accessibility”, 27-28 October, Edinburgh