Grey Line (Bangkok)

The Grey Line is a planned monorail line in the north of Bangkok to be built from Watcharaphon to Thong Lo. The route would provide a vital north - south link for a distance of 16.25 km with 15 planned stations and is expected to cost 27 billion baht. The line would support the growth of residential areas around Pradit Monutham Road and Kaset-Namawin road corridors and is forecast to eventually have 370,000 passengers per day. The BMA Grey will interchange with other lines including the MRT Pink Line, the proposed MRT Brown Line, the MRT Yellow Line, MRT Orange Line (under construction) and BTS Sukhumvit Line.

The BMA contracted a consultants study into the project which was due to be completed by March 2022. A new EIA for the line was completed and approved by the National Environment Board in early March 2022. On 17 March 2022, the BMA held a market sounding seminar with companies interested in potentially bidding for the line and updated that the feasibility study would be completed by early June 2022.

The BMA proposes to gain Cabinet approval for the line in 2023 and identify private investor partners in 2024-2025 with a view to commencing construction in 2026 in order for the line to open in 2030. However, BMA transferred the project to the Mass Rapid Transit Authority of Thailand (MRTA) on December 27, 2024, as it is believed that consolidating the project under a single owner will enable better control of fare prices, preventing them from becoming excessively high. After the transfer, the MRTA will reassess the project to determine the feasibility of further construction.