The results of a research project focused on route choice simulation, both comparing the performances of route choice set generation methods and estimating different route choice models, on the basis of real data collected within the metropolitan area of Napoli, Italy are described. In more detail, the context can be classified as urban, but with a significant numberof motorway connections between the downtown and the suburbs. The networkhas been implemented on the basis of a TeleAtlas network database. Network characteristics have been also compared with data already available, therefore providing reliability on directly measured link characteristics. Data are being collected through a computer-aided interview process, based on interactive maps and on an automatic procedure for data collections and storage. With reference to route choice set generation methods, the most widely adopted procedures follow a deterministic approach, i.e. they defineexogenously a route choice set on the basis of reasonable heuristic rules. Their reliability is normally measured through some indicators based on the calculation of the percentage of the observed paths classifiable as reproduced by the generated paths, according to a certain threshold: the most relevant are the percentage coverage and the consistency index indicators. Such indicators do not take into account how many additional links and paths not belonging to the set of observed paths are generated to reach a satisfactory coverage. Since this kind of bias can lead to significant errors in traffic assignment and model estimation, the same coverage indicators above defined have been considered in this paper also with reference tothe set of generated paths towards the set of observed paths, i.e. checking directly whether a generated path is significantly different (e.g. longer) with respect to the observed paths it is trying to reproduce. Moreover, the two types of indicators have also been combined together in order toprovide aggregate performance measures. The main result is that exploringa significant part of the network (i.e. generating not much overlapped paths) normally leads to a higher coverage, but a higher number of links notbelonging to any observed path are introduced at the same time. Therefore, the quality of a route choice set generation method should be measured on the basis of its robustness with respect both to coverage and bias: fromthis standpoint, the best results have been provided by the randomizationmethod, which is also the less computational effort demanding. Analogous analyses have also been carried out with reference to a disaggregation by origin-destination pair. With reference to the route choice model estimation, different aspects have been investigated and addressed: (a) the influence of choice set generation on route choice estimation, i.e. which choiceset generation methods offer higher reliability and stability in model estimation; (b) whether MNL models with path-size and commonality factor terms provide for a better goodness of fit with respect to more complex modelstructures; (c) whether a positive sign for the path-size coefficient is obtained also in this dataset, providing evidence for the presence of a diversion effect behaviour. Secondly, in order to take into account the previously mentioned bias in the route generation phase, a different specification of the likelihood function to be minimized is proposed for the route choice estimation context. Consistently, theoretical aspects are discussedand the corresponding estimation results compared with those provided by the standard likelihood function. For the covering abstract see ITRD E137145.
Abstract