The Blue Line Extension expands the initial mass rapid transit system in Bangkok, the MRT Chaloem Ratchamongkhon Line, from Hua Lamphong to Bang Sue. Total length of the extension is approximately 27 km and consists of 2 sections:

Bang Sue – Tha Phra Section, the so-called “Circle Line” - Elevated structure across Chao Phraya River and along Charan Sanitwong Road, 13.1 km in length with 7 elevated stations.

Hua Lamphong – Bang Khae Section -  Includes 4.8 km underground (crossing Chao Phraya River), and 8.9 km elevated structure, primarily along Phet Kasem Road.

NCE was responsible for design of all elevated guideway structures. The typical structure is a double-track viaduct designed as precast segmental box girder continuous over three 35-meter spans, supported by single columns in the road median. In locations without a median or where columns would cause hindrance to the traffic flow underneath, the viaduct is supported by portal frames.