Data were averaged over 2010-2015. The DfT produced a lookup for LHAs (Local Highway Authorities) to FUAs. Some LHAs might only partially overlap with the FUA, in which case a fraction of their traffic volume is accounted for in the FUA total. This fraction is assumed to be proportional to the spatial overlap, an assumption which of course induces great uncertainty in the results. In two of the FUAs in the United Kingdom, traffic volume data could not be computed because boundary mismatch caused an uncertainty on the traffic volumes which was greater than +/-30%. This is observed in the vast majority of cities (61 out of 68) where data is provided by gender.