The northern section of the Purple Line will begin a trial run late next year before a full commercial service in mid-2016.
The Bang Yai-Tao Pun section has been ahead of schedule, with construction 90% complete and train system 24% done.
A free trial run is set for late 2015 and the commercial service will begin in the middle of 2016, 3-6 months ahead of the original schedule, said Yongsit Rojsrikul, governor of the Mass Rapid Transit Authority of Thailand (MRTA), on Monday.
The northern section is 23 kilometres long, with 16 stations.
According to plan, the proposed 19.8km southern section of the line will run from Tao Pun to Phra Pradaeng in Samut Prakan.
The MRTA also showcased on Monday the train to be used in the route.
As for other mass transit lines, Mr Yongsit said the MRTA would soon issue the terms of reference for the 18.4km Dark Green Line (Mor Chit - Sphan Mai - Koo Kot), according to a Thairath Online report.
They are for four contracts with total value of 29 billion baht.
The MRTA hopes to sign the contracts by the end of this year.
The first contract is for the construction work from Mor Chit to Saphan Mai worth 14.02 billion baht.
The second is for the construction work from Saphan Mai to Koo Kot worth 6.13 billion baht.
The third is for the construction of a 3.71-billion-baht maintenance centre and parking building.
The last is for the design, procurement and installation of the electric rail system worth 2.61 billion baht.
As for the 27km extension of the Blue Line (Hua Lum Phong-Bang Kaew and Bang Sue-Tha Phra), the MRTA agreed with a 2010 study that Bangkok Metro Plc, the existing operator, should run the extension.
It is in the process of considering the details before the project is submitted to the National Council for Peace and Order for approval.
Construction of the Blue Line extension, slated to be operational in late 2017, is half complete.
Sombat Kitjalak, CEO of Bangkok Metro, the operator of the subway, said it had the readiness to operate the extension lines, which would use 28 trains with three cars each, to be bought by the MRTA.
