Both the Royal Statistical Society and the Institute of Actuaries are interested in the collection and analysis of data and the use of the results for forecasting possible future trends. This paper deals with future traffic estimates of the number of passengers likely to use new underground railway facilities and the likely effect on the existing underground railway networks and other methods of transport, both public and private. It does not deal with the future planning of main line railway suburban services; nor does it deal with the civil engineering and operational problems of construction, although, of course, the capital cost of construction for a new tube and the capital cost of rolling stock have to be taken into account in considering the financial prospect of any new schemes.