Aggregation of gravity models for journeys to work

This paper deals with the use of gravity models to examine journeys to work. The purpose of the paper is to study very simple examples demonstrating that gravity models may be subject to serious misspecification in aggregate systems. As an outcome of the theoretical analysis, the paper has several implications to empirical work. It suggests a variety of modifications, experiments, and testing regimes that can be carried out to examine the performance of gravity models for journeys to work.