The Department of Rail Transport (DRT) is planning to develop four new mass transit rail lines in Thailand. The agency has proposed the development of a 8.8-km-long line between Rangsit and Thammasat University, a 5.7-km-long line connecting Taling Chan and Siriraj, a 14.-km-long line spanning Taling to Salaya as well as a 22.1-km-long Brown Line between Khae Rai and Bueng Kum.

These four projects will require a total estimated investment of around THB63.4 billion. The lines are expected to open to passenger service in 2029.

After conducting extensive public hearings to assess the rail requirements of commuters in and around Bangkok, the Department has selected the final four routes from the 33 routes recommended in its M-MAP 2 master plan for rail transport in the region.