Household travel surveys (HTS) have been conducted for more than 40 years all over the world but their potential for analysing travel behaviour over time and for different regions has not been fully utilised. Two main reasons exist for this limited use of the existing data. First, amalgamating data over time and across study areas is burdensome, and second, it is not clear whether meaningful results can be achieved because of differences in the survey characteristics. This paper develops a method for ex-post harmonising, mixed-method, cross-sectional HTS. The harmonisation includes the areas of survey coverage, survey definitions and survey methods. The spatial harmonisation based on the density of residents and the temporal harmonisation based on the definition of comparable survey periods are introduced as further harmonisation steps. The harmonisation method is developed and successfully validated based
on HTS from five European capital cities: Berlin, Copenhagen, London, Paris, and Vienna. Key travel estimates match well between the cities and the developments over time are smooth, except for walking. All analyses including walking trips require special care. The result of the data harmonisation is a pooled database that has an enormous potential for analysing travel behaviour based on historical HTS.