Social costs of transport are basically equal to the sum of all costs of mobility and may be separated into internal costs, external costs and government expenditures (though there is some overlap in this categorisation). Internal costs are private expenditures on transport, apart from transport taxes. All costs that households and firms make for transport could be included, e.g. costs of depreciation and maintenance of vehicles, ships and aeroplanes, costs of insurance, fuel costs, costs of train tickets and freight prices.