Due to the increased number of population, every day from the periphery to the centre and backwards, big passenger flows are being formed. The necessity of efficient public transport in the direction of the largest passenger flows, transport and environmental problems of the city have imposed the start of the construction of the metropolitan in Sofia. Following the ratified by the Council of Ministers of Bulgaria a Technical and economic report on the metro and the approved General City Plan, the General scheme for the development of the lines should consist of three diameters with extensions in the periphery, with total length of 65 km, 63 metro stations, and 1,2 million daily passenger capacity at the final stage of implementation.

 General scheme for the development of the metro lines according to the General Master Plan of Sofia 

The first diameter “ Obelya RD – Lyulin RD – Centre – Mladost RD – Druzhba RD –Sofia Airport” will be 29 km long and will consist of 23 metro stations.
The second diameter “Lozenets RD – Centre - Ilientsi quarter” will be 17 km long and will consist of 17 metro stations. The third diameter “Knyazhevo quarter– Centre- Poduyane RD - V. Levski RD” will be 19 km long and will consist of 23 metro stations.
The diameters intersect into a triangle in the city, thus each section of the metro route could be reached within one single change of the line.
Main technical characteristics of the metropolitan, according to the Technical- economic report are: average distance between the stations-1100 m, operational speed of the rolling stock -90 km/h, maximum carriage capacity - 50 thousand passengers per hour in one direction, minimum permissible interval between the trains- 90 sec., 1435 mm rail gauge, power supply of the rolling stock with a nominal DC voltage of 825 volts through a contact rail.

Table 1 Main parameters of the Metro in Sofia and the general scheme for the development of its lines, according to the Technical-economic report:

   Metro construction started with the busiest first metro diameter, where the biggest passenger flows are being formed and with prognosticated maximum values of up to 38 thousand people in peak hours.