The study will be carried out by a consulting firm and cover two urgent projects, OTP deputy director-general Chaiwat Thongkamkoon said.
The routes are a 737-kilometre stretch linking Nong Khai, Khorat, Saraburi, Laem Chabang and Mab Ta Phut at a cost of 392.5 billion baht, and a 655km stretch from Chiang Khong and Den Chai to Ban Phachi at a cost of 348.8 billion baht.
The two routes are pilot projects for wider 1.43 metre tracks.
The selected consulting firm will sign a contract in October and the study is expected to take about one year, Mr Chaiwat said, adding the construction of the two rail routes should be complete by 2021.
According to Mr Chaiwat, a new government railways agency will be responsible for the investment and will have to work with other state agencies to finance the scheme, either from the budget, a loan or an infrastructure fund.
The State Railway of Thailand will handle the practical operation of the trains. It will either run the train service itself or privatise it, he said.
Mr Chaiwat said a Chinese commercial attache met transport permanent secretary Soithip Traisuth last week and has confirmed China is interested in jointly investing in the rail construction projects.
The attache also asked that a previous deal made between Thailand and China on the formation of a joint venture to invest in the project be reconsidered. Mr Chaiwat said the military government will decide whether to revisit the venture, which was set to include the Thai government and Thai and Chinese private companies.
“China is interested in investing as it has a mutual economic dependence with Thailand,” Mr Chaiwat said. “The two electric rail routes would be a gateway to commercial links with China.”
He added that China is about to construct high-speed railways linking Laos and Thailand.
Deputy permanent secretary for transport, Chanchai Suwisuthakul, said the two routes will support speeds of up to 180km per hour and focus on the shipment of goods between Thailand, Laos and China.
He said the second phase of double-track rail development, which will be carried out between 2022 and 2029, includes three routes between Tak-Phitsanulok-Ban Phai, Nong Khai-Ubon Ratchathani, and Ban Phachi-Bangkok-Padang Besar.