The aim of this series of maps is to present the spread of motorways in Europe through the twentieth century. The key indicator for the economic potential of the infrastructure is the length of the motorways in operation, given in km. Motorways are roads for motorised traffic only. This type of road is further characterised by the existence of a barrier to separate lanes for traffic in opposite directions and a limited amount of access points. The name for this type of road varies from country to country. In Germany it is called Autobahn, in Italy Autostrada, in Spain Autopistas or Autovias (the first are generally toll roads, the latter are not). In France motorways are called Autoroutes, in the Netherlands and the Flemish speaking parts of Belgium they are known as Autosnelweg, as Interstate Highways in the USA, and so on. In general, there is consensus that these terms cover the same type of road, although one could discuss whether the first Autostrade in Italy – also known as Raccordi- were motorways under the definition just given, since they did not had a separation of the lanes for opposite traffic. The data charted in these maps has been taken from the TIE-Database and a variety of transnational sources, most importantly from the World Road Statistics, published by the International Road Federation. The scale of these maps, which have been produced using a geographic information system (GIS), varies, so direct comparisons between maps are only possible by taking account of the scaling key in the legend. It should be noted that motorways in the Soviet Union / Russia have not been graphed due to due to missing data.