The M.R.T. Chaloem Ratchamongkhon Line, was preliminary designed in 1992 as an elevated rail except a portion at the southern end station (Hua Lamphong Station) which is underground section for future extension to the densely populated area. As environmental concerns have been increasing, the cabinet in 1995, decided the project to be entirely underground. The route starts from Hua Lamphong railway station and runs along the Rama IV Rd. passing Silom area, Lumphini Park, Klong Toey area, and turns left onto Ratchadaphisek Road passing Queen Sirikit National Conventional Center, Asok area, Suthisan area and turns left again onto Lat Phrao Road passing North and Northeastern Bus Terminal and finally ends at Bang Sue railway station. The alignment is generally along the centerline of the roads. The vertical alignment is ranging from approximately 14-30 m. below the existing road surface.