Accessibility Evaluation: There?s More to It Than Just Summing Up Travel Cost Reductions
B Zondag, G de Jong, M de Bok, Significance,NL; K Geurs, Netherlands Environmental Assessment Agency, NL; M Pieters, Stratelligence, NL
This paper presents an application of TIGRIS XL (a LUTI model), in which the logsum approach has been applied to calculate the accessibility impacts (of several land-use and transport strategies) and express these impacts in monetary terms.
Conventional methods to measure accessibility in cost-benefit analysis are not capable of measuring all accessibility benefits of integrated land-use/transport strategies. Conventional methods are here defined by the frequently applied rule-of-half project appraisal method in combination with changes in travel times (or congestion time). Such an approach is incapable of calculating all the accessibility effects of land-use policies, as it does not value changes in the land-use pattern. The land-use effects are only indirectly valued as they affect travel production or times/costs, which seems to be an implausible approximation for these benefits as it does not address in a direct way changes in the travel opportunities at the locations. It should be noted that current practice is also not fully measuring the impacts of transport policies as land-use effects resulting from such policy are not valued.
This paper first presents an approach to calculate the accessibility effects of integrated land-use and transport strategies. In a second step, these accessibility effects are converted into monetary costs or benefits. The method has been applied within a large-scale policy study to evaluate the accessibility effects of several integrated land-use and transport strategies in the Netherlands.
In the first step the changes in accessibility are calculated by the TIGRIS XL model; an integrated land use and transport model that has been developed for the Transport Research Centre in the Netherlands. The land-use model uses discrete time steps of one year to generate population segmentation and employment figures by zone. The land use model incorporates four components: a demography module, a land-use and real estate market module, a housing market module and a labour market module. Every five years a dynamic integration is made with the National Model System (NMS), the transport model for the Netherlands.
The NMS is a discrete choice type of transport model based on micro-economic utility theory. With such a model it is possible to generate a logsum value for each tour, an aggregate value expressing the utility from alternative modes and characteristics of the destination locations. This logsum represents the accessibility impacts of changes in land-use patterns, which is an important advantage of the logsum method compared to conventional project appraisal using travel speeds or costs in combination with the rule-of-half method. A second advantage of the presented framework is that the use of a land-use and transport interaction model makes it possible to extend ?traditional? accessibility indicators by including changes in land-use as a result of the strategy.
The logsum change, defined as the difference between the expected utility of a variant and the reference case, represents the change in the consumer surplus. To value the change in consumer surplus (?utility?), the ?standard? set of values of time used in project appraisal can be used (e.g. from stated preference studies). An alternative valuation method is to use the set of values of time that is implied by the utility coefficients of the NMS itself, which might be preferred for reasons of consistency. However in this study we have used the standard set to make the findings of the logsum approach more comparable with those of the conventional method (that uses the same set of values of time).
In the application of TIGRIS XL for the ?spatial impressions? project for the Netherlands Environmental Assessment Agency (MNP) the accessibility impacts of several land-use and transport strategies have been calculated and expressed in monetary terms. These include a retreat variant, which basically means no growth in the Western part of the Netherlands, and an urban concentration variant with a concentrated development in and around existing urban centres. Furthermore several transport strategies have been tested in combination with the urban concentration variant, such as an infrastructure construction program, a congestion charging strategy or a combination of both. For all strategies the impacts have been calculated by applying the rule-of-half method as well as the logsum method. Preliminary conclusions are that:
? Land-use policies do have a substantial impact on accessibility measures and should not be ignored in the evaluation;
? The rule-of-half method is not capable of addressing these effects of land-use policies on accessibility; the application illustrates that the rule-of-half method can result in effects with the wrong sign.
Association for European Transport