The cabinet has given the green light to the 323km double-track rail route from Den Chai to Chiang Khong in the North.
The 85-billion-baht project was tabled before the cabinet in March, but it didn't get the go-ahead until Tuesday. The construction will link four provinces -- Phrae, Lampang, Phayao and Chiang Rai -- and have 26 stations and four tunnels.
"The government wants to see more investment in rail infrastructure, 90% of which is still single-track routes," Natthaphon Jatusripitak, an adviser to the Prime Minister's Office, said after the cabinet meeting.
Under the single-track system, trains running in both directions have to share the line, but with the double tracks, they are not required to wait for their turn to move.
"Such travel [on single tracks] wastes time and increases travel time from 8 to 12 hours on some routes," Ms Natthaphon said.
The Den Chai-Chiang Khong double-track route, which was initiated about five decades ago, has faced several delays, including the need to conduct a new study in 2004 into how it will connect with China's initiative to expand rail networks southward.
According to the construction plan, the route will start at Den Chai station, in Phrae, which connects to Thailand's present northern train line from Hua Lamphong in Bangkok to Chiang Mai.
It then travels up north, where it will enter Lampang through the province's Tambon Mae Tip station in Ngao district. Further north, the route will enter Phayao through Phayao University station.
After reaching Chiang Rai through Pa Daet district station, the route's terminus will lie in the province's Chiang Khong district, which borders Laos.
"The new route is expected to open between 2022 and 2023," a source from the State Railway of Thailand said.
He could not give a date for bidding for the project, reasoning the SRT needs to wait for land expropriation to start first.
The line will require a 50-60m wide strip of land along the length of the route.
This new double-track rail route is also under the state plan to facilitate transport to Ban Huak, Phayao's bustling trade area adjacent to Laos.
Ban Huak will soon become a "permanent" border checkpoint, government spokesman Sansern Kaewkanmerd said Tuesday, referring to another cabinet resolution.
Border trade at Ban Huak, located in Phu Sang district, attracted authorities and businessmen over the past five years with trade value growing to 1.38 billion baht annually.
Over the same five-year period, up to 215,000 Thai and Lao people also used Ban Huak as a key transport link between the two countries, he said.
"The opening ceremony is set for Aug 8," Lt Gen Sansern said.
Thailand has already started several road projects to connect will Ban Huak. The latest one -- a Ban Huak-Kio Hok route in Phu Sang district -- is already listed on under the 2019 budget.
Lt Gen Sansern emphasised that officials will crack down on illegal immigration and transnational crimes.