The Grey Line (Vatcharapol - Lat Phrao - Rama IV - Rama IX Bridge) is one of the planned monorail line in Bangkok, Thailand. Its path runs along the north - south axis. This line is to support the growth of residential areas around Pradit Manutham Rd. and the Sathupradit area in Yan Nawa District. The route runs from Ram Indra Road, on the northeast outskirts of Bangkok, down south through Pradit Manuthum Rd. along the Chalongrat Expressway going into the downtown district of Thong Lo. From there, it passes through Sukhumvit Rd., Rama IV Rd., and Ratchadaphisek - Rama 3 Rd. It ends at The Rama IX Bridge in the south of the downtown Bangkok. The total distance of the route is approximately 26 km and is expected to service 340,000 passengers per day.
The BMA stated in mid 2013 that it considers the Grey monorail line a priority and planned to progress planning by completing an EIA by the end of 2013 for the line to be tendered by early 2014. If approved, construction would take place from 2015 - 2017 for opening in 2018. In March 2014, the OTP stated that they would contract a consultant to undertake further study of the Grey Line. In May 2014, a consultant was contracted to undertake a financial feasibility study of the line which is expected to complete its work by the end of 2014.
The BMA is also considering a possible Phase 2 extension along the length of Rama 3 rd, over the Chao Phraya river and along Ratchadapisek rd (Inner Ring rd) to Tha Phra to replace the BRT along this route. This would enable the Grey Line to interchange with the BTS Silom Line at Talat Phlu station, the future MRT Purple Line (Phase 2) southern extension and link with the MRT Blue Line extension at Tha Phra station.