STATISTICAL BACKGROUND FOR THE PLANNING OF EXTENSIONS TO EXISTING UNDERGROUND RAILWAY NETWORKS by F. J. LLOYD (A paper discussed at a joint meeting of the Royal Statistical Society, General Applications Section and the Students' Society on 18 November 1966) 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 engin- eering 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. Underground railways involve a large capital cost and once they are built they are difficult and expensive to alter. Even a relatively simple additional station on an existing underground line is likely to cost at least £1 million in capital costs. But the capacity of an under- ground to move very large numbers of people in cities is unrivalled. With modern station layout and advanced automatic signalling devices it is possible to plan to run on a single track up to 40 trains of eight coaches each in any one hour. Such a service would have the capacity to carry up to 30,000 or more passengers in one hour pro- vided the potential passengers presented themselves evenly. In practice, however, passengers do not so regulate their travel require- ments and one feature of peak hour operation in London is the very heavy surges of passengers both on to and off the Underground at certain stations. While planning is related to passengers per hour, it is essential not to overlook the higher loadings in the critical quarter of 115 116 F. J. LLOYD an hour at the top of the peak. However, an underground railway has a great overload capacity, so that it can deal with short-time surges of traffic even if the loadings of individual trains or cars should be unevenly distributed. At the other end of the scale, the bus has a low capital cost, is extremely flexible as regards routeing and stopping, but has a much lower carrying capacity. For example, if it were possible to reserve a special lane for buses with stops every quarter-mile and no over- taking, the planned capacity of that lane would be no higher than about 100 buses per hour which, with a full load of 80 persons per bus, would amount to 8,000 passengers per hour. If laybys were introduced for stops and buses permitted to overtake each other and the stops widened to a mile apart the planned potential capacity might be increased to 150 buses per hour and 12,000 passengers per hour, per lane. Without reserved lanes the capacity would be less. For comparison a lane used only by private cars could accommodate 1,000 to 1,500 cars per hour. Car commuters to London average 1½ persons per car including the driver, so that private cars moving into or out of London in the peaks move about 2,000 people only per lane. From time to time various other technical methods for public transport in urban areas are proposed. There are difficulties in constructing overhead monorails or suspended railways in fully built- up cities because of the destruction of property and amenities. Difficulties of interchanging from one form of transport to another are magnified in an established city with existing surface and under- ground transport. For new cities or for transport over difficult terrain there may well be applications. At the present time a feasibil- ity study is being undertaken in Manchester of a possible monorail link between the city centre and an outlying suburb. There are other ideas, apart from monorails, but they are not discussed in this paper. In practice to obtain high rates of passenger movement within a city requires expert planning and operation under rigid control within a space used solely for that purpose. These conditions can be achieved by an underground railway; they are very difficult to achieve on the roads. In cities with recently developed underground railway systems, and in the early days of underground construction in London, the railways have played an important part in attracting new traffic and opening up the development of virgin land. For example, Stockholm is a city surrounded by lakes and inlets of the sea and there was no PLANNING UNDERGROUND RAILWAY EXTENSIONS 117 available land near to the city centre for housing development. By building an underground railway under various water barriers, it became possible to link newly built suburbs to the city centre. Similarly in London, the early extensions of the Northern Line from Golders Green to Hendon Central and Edgware in 1923-24 in the north, and from Clapham Common to Morden in 1926 in the south, had a major impact on suburban developments. The capital to finance these two London projects was raised by a redeemable debenture guaranteed by H.M. Government under the powers of the Trades Facilities Act 1921-22. The interest payments on this capital were borne by the Common Fund of the Underground group of companies which included the London General Omnibus Company. The importance of the financial contribution of the bus company was underlined by Mr Frank Pick, vice-chairman of the London Passenger Transport Board, who once said, 'It requires certainly two, and possibly three, road miles to support one rail service mile'. He was referring to the conditions of the 1930s and for various reasons the same is not true today. One reason why underground railways are so expensive to finance is that the heavy capital investment is used near to capacity to carry the intensely peaked commuter traffic only twice a day, only five days a week. The split of the density of such underground passenger traffic in London by hours of the day is given in Table 1, taken from the London Traffic Survey, Vol. 1, Table 6-9. Table 1 Weekday journeys inside the survey area by residents of the survey area by periods of arrival Percentage of Journeys by Underground by Period of Arrival Terminating in Terminating in Survey Area Central Area Early morning off peak 7.6 7.9 Morning peak (2 hours) 301 49.7 Midday off peak (7 hours) 191 20.7 Evening peak (2 hours) 31.6 160 Evening off peak 11 6 5.7 Total (24 hours) 1000 1000 The survey area covers 941 square miles with its boundary 15-20 miles from Charing Cross and includes most of the underground system; the central area covers about ten square miles. 118 F. J. LLOYD It is seen that very broadly during one-sixth of the hours of operation over a week two-thirds of the passengers are carried mainly in one direction only. Before condemning these figures as unproductive, remember that the life of London depends on its underground services. Apart from providing direct commuter facilities for dormitory areas, the London Underground has the function of distributing commuters from main line stations to their offices or other work places in the central area. As a result of future changes in population and employment patterns, it is expected that the number of outer suburban commuters, mainly using the suburban railways, will increase and additional underground facilities will be required to distribute these passengers in the central area. A further reason for creating new underground railway facilities in central London is the need to relieve overcrowding on existing underground lines. Not only can the points of congestion be eased and the passengers given reasonable travelling conditions, but other parts of the existing underground network can be brought into more pro- ductive use. For example, the Victoria Line when in operation will ease the present intense loadings between Victoria and Charing Cross on the District Line in the morning and evening peaks. A further very necessary relief will be given on the Piccadilly Line immediately north of Kings Cross. In both examples it has been estimated that the easement will amount to 20 to 25% of the present crush loading conditions. Yet another reason is the need to provide relief to traffic-con- gested streets. The 20th century has seen the fantastic growth in private transport brought about by the motor car. It is clear from North American experience that one of the problems of the present is to learn how to live in cities with the private car. Recent American experience shows a realization that the private car alone cannot move everyone into and out of cities, and there has been a resurgence of 'rapid transit' (or underground railways in London terms). Great cities clearly need an underground railway network with 'park-and- ride' facilities which will tempt the motorist to leave his car at his local station or at a convenient station nearer the centre, and to continue his journey by underground railway. In considering underground railway planning in London it must be remembered that while the origins of the underground system might be regarded as a series of historical accidents rather than the PLANNING UNDERGROUND RAILWAY EXTENSIONS 119 result of an overall plan, it would be truer to say that there were plans but there were too many and they were not co-ordinated.