Bangkok Metropolitan Administration’s Traffic and Transportation Department has announced that the Environmental Impact Assessment (EIA) for Bangkok’s planned Grey Line monorail project (Thailand) has been completed and will be submitted to the National Environment Board.

The 40 km long Grey Line, expected to serve the needs of about 140,000 commuters daily, would link Watcharapol and Tha Phra via the Rama IX Bridge, in the southern part of downtown Bangkok. It would connect with other commuter lines including the MRT Pink Line, MRT Yellow Line, MRT Orange Line, SRT Light Red Line and BTS Skytrain Sukhumvit Line, helping ease traffic congestion in th city.

Panya Consultants, Phisut Technology, Ensol and Trans Consult were hired in 2014 as construction consultants. Their main tasks included conducting research studies for the project's overall operation and preparing the EIA study to be submitted to state agencies.

Construction is planned in three phases:

• Phase 1 - 16.25 km between Watcharapol and Thong Lor.
• Phase 2 - 12.17 km between Phra Khanong and Rama III
• Phase 3 - 11.49 km between Rama III and Tha Phra

Phase 1 is expected to require three years to complete and it will require an investment of THB27-30 billion (US$570 - 860 million).