The Mass Rapid Transit Authority of Thailand (MRTA) has given in-principle approval for the development of a new monorail line, the Brown Line. The 21.6 km line will cover 22 stations connecting Kae Rai, Ngam Wong Wan Road, Kase–Navamin Road, and Lam Salee. The line will be developed as a feeder linking the Pink Line in Kae Rai, the Purple Line on Rattanathibet Road, the Red Line at Bang Khen prison, and the Green Line at Kasetsart University. The MRTA is planning to utilise the existing pillars in the centre of Kaset–Navamin Road built by the Expressway Authority of Thailand. The estimated investment for the project is 45 billion baht. The final plan is expected to be submitted to the Ministry of Transport by September 2013. Design work is expected to be completed by 2016, and bids are scheduled to be invited in 2017. Construction will take at least three years. Operations are expected to be launched in mid-2021. In an update on the Purple Line, the MRTA has stated that construction work is 75 per cent complete and that commercial operation is expected to start in 2016. The line is divided into two sections: the 23 km Bang Yai–Bang Sue section covering 16 elevated stations (estimated investment 60.18 billion baht) and the 20 km Tao Poon–Rat Burana section covering 16 underground stations (estimated investment 73.78 billion baht). Currently, discussions are under way between Bangkok Metro Public Company Limited and the transport committee for a reduction in the operations and maintenance cost of the Purple Line by 200 million baht. In addition, the implementation of the Bang Sue–Taopoon extension on a public–private partnership basis is also being considered.