Under the metro expansion scheme, lines 3 and 4 will add 37 kilometres and 24 kilometres respectively to the existing network. According to the tender specifications, about 24 kilometres of line 3 and 22 of 32 stations will be located underground. Line 4 requires the construction of 19 kilometres of underground track and 21 of the 22 stations will be underground. Bidders on the project are required to submit their own financing proposals.
Tehran’s existing metro network comprises two lines. Line 1 links a 34-kilometre stretch between Mirdamad in the north and the mausoleum of Imam Khomeini in the far south of the capital, while line 2 connects the eastern and western parts of Tehran over a distance of 20 kilometres. Works on line 1 and 2 were carried out by local firms, with technical support from Chinese companies.