Challenges for Europe and North America
Edited by Karst T. Geurs, Kevin J. Krizek and Aura Reggiani
Chapter 4: Assessment of infrastructure investments using agent-based accessibility
To evaluate transport infrastructure projects, it is common practice in Switzerland and elsewhere to perform a cost–benefit analysis ex ante. To assess the benefits of the investment, guidelines usually propose to predict travel time savings and to monetize them using values of travel time savings (e.g., VSS, 2006; FGSV, 1997). Travel time savings originate due to higher capacities on congested links and higher speeds on better aligned links. To predict the expected reductions, standard transport models usually allow for changes in route and mode choice as the relevant behavioural dimensions of travellers. However, one can hypothesize that travellers also alter departure time, destination or location (starting point) to adapt to new transport infrastructure. Consequently, a model that does not consider departure time and destination or location choice would not include all effects arising from an adapted transport infrastructure, especially in a long-term perspective. A model that neglects relevant degrees of freedom likely produces misleading results in terms of calculated traffic volumes leading to misjudged utility gains. This issue was recently discussed in depth by Metz (2008). The integration of other dimensions of decision-making in order to calculate future traffic flows raises the question whether short-term travel time savings are still an appropriate indicator to judge an infrastructural investment given the long lifetimes of infrastructures. When we assume that travellers change not only their connections but also destination and departure time, we should integrate utility components influenced by such decisions into our models to maintain consistency. Therefore we want to show that it is relevant for evaluation whether we only consider travel time savings or more comprehensive welfare indicators like accessibility. Accordingly, this chapter addresses the following research questions:
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