The MRT was constructed under a concession concept. For the first MRT line, officially known as Chaloem Ratchamongkhon or informally as the "Blue Line", most civil infrastructure were provided by the government sector, Mass Rapid Transit Authority of Thailand (MRTA), and handed over to their concessionaire under a 25-year concession agreement. Bangkok Expressway and Metro Public Company Limited (formerly known as Bangkok Metro Company Limited) is the only private sector company that won a bid in MRTA's concession contract for the blue line. As MRTA's concessionaire, BEM provides M&E equipment, including electrical trains, signalling systems, SCADA, communication, PSD, etc. for the subway project and fully operates the system. To maintain the system, BEM has subcontracted in 10 years to Siemens which was the M&E system supplier since system opening and 7 years maintenance contract to two local maintenance services for north and south line.