Spatial aggregation bias in trip distribution probabilities: The case of the opportunity model

In estimating trip distribution probabilities by the opportunity model, the conventional method regards a region as a set of “point zones”, and hence inevitably yields a spatial aggregation bias. First, we show that the conventional method overestimates an intra-zone trip distribution probability and underestimates an inter-zone trip distribution probability. Second, it is presented that the inter-zone relative spatial aggregation bias depends only on an origin area, and that the spatial aggregation bias is independent of the spatial aggregation in the intermediate area. Finally we obtain the minimum number of zones required to ensure that a given level of bias is not exceeded.