For the pre-planning of a metro system it is important to have a good knowledge of tile ground conditions. If unforeseen circumstances are discovered later it is often almost impossible to change the placement of stations and the route alignments. The metro system of Helsinki was therefore planned with a great accuracy already at an early stage and with the conditions of the rock, soil, groundwater and foundations of the buildings thoroughly investigated. Special maps showing these conditions were used at the pre-planning work.
The first section of the Helsinki metro system will be inaugurated in 1982. The line will be 13 km long and include 9 stations and will link the city centre of Helsinki with one of its north eastern suburbs. The decision to build a metro system for the half a million inhabitants of the Finnish capital was taken in 1969. But before the detailed planning and construction work could begin, a comprehensive study had to be made to plan and select alternative routes. And it is this important pre-planning stage that is the subject of this paper. In principle the pre-planning stage can be divided into three main sections •See Fig. 1. The first
includes the regional metro system and studies of alternative routes. In the second stage
the various routes of established lines are studied. This is used to help select a route which will provide the best possible transport service for those parts of the city and urban areas that the new line will serve. At the third
and final stage of preplanning, different routes are studied with a view to the technical demands involved. Alternative sites for ticket halls with exits leading to ground level are also studied.
The placement of stations is analyzed as well as the type of stations, which is selected and adjusted according to the possibilities for the placement of ticket halls, the technical prerequisites for construction, line geometry, and so on. Without a doubt it is this third pre-planning stage that is the most important in the job of creating a new metro system. This is why we have chosen to give you a general breakdown of how the planning of several aspects of the new metro system in Helsinki has been carried out.
To be able to plan a regional metro system all general pre-conditions must be identified. This is largely a question of regional planning involving general estimates of the volume of traffic, population development etc. Demands concerning the environment and the technical standards of transportation required must also be made at this stage. When it comes to Helsinki many different alternative routes and branches have been discussed and analyzed. Figure 1 shows the two routes included in the plans for the metro system in Helsinki.
At the preliminary route planning the number of stations and their approximate sites are established. As it is the stations that involve the majority of the building costs in a metro system the distance between each one must be carefully calculated.