Thailand’s longest rail tunnel project passes 53% completion milestone
The Den Chai–Chiang Rai–Chiang Khong double-track line is now 53.421% complete as of January 2026, with three of its four tunnels running ahead of plan and services preliminarily expected to begin in 2028.
- The Den Chai–Chiang Rai–Chiang Khong double-track railway project has reached 53.4% completion, which is slightly behind its planned schedule.
- The 323.1 km route is a key infrastructure project designed to enhance transport capacity, cross-border trade, and tourism in northern Thailand.
- A major feature of the project is the construction of four tunnels, including what will be Thailand's longest railway tunnel at 6.2 km.
- The new railway line is preliminarily expected to open for service in 2028.
The new double-track railway project, Den Chai–Chiang Rai–Chiang Khong, is an extension of the route into Chiang Rai, linking to the border at Chiang Khong.
It is a key route that will help enhance the country’s rail transport capacity, especially in the North, to support the expansion of cross-border and transit trade, as well as connectivity with the Greater Mekong Subregion, which continues to grow.
The Den Chai–Chiang Rai–Chiang Khong railway construction project is one of the rail development projects under Thailand’s transport infrastructure development strategy, Programme 1: Intercity Rail Network Development, Phase 3, aimed at improving rail service capacity.
This project will include the longest railway tunnel in Thailand, and is expected to become a new tourism route.
It is preliminarily expected to open for service in 2028.
The alignment starts in Den Chai District, Phrae Province, and ends in Chiang Khong District, Chiang Rai Province, spanning 323.1 kilometres. It passes through 59 subdistricts, 17 districts, across four northern provinces: Phrae, Lampang, Phayao, and Chiang Rai.
There will be 26 stations in total, comprising four major stations, nine minor stations, and 13 halts.
Facilities have been designed in line with Universal Design principles, and boundary fencing along the right-of-way has also been designed.
This also includes railway bridges and 40 road bridges crossing the railway, as well as 102 road underpasses beneath the railway.
There will be link roads for traffic distribution, along with overpasses, footpaths, and motorcycle crossings and underpasses, addressing 254 rail crossing points along the route to safely increase operating speeds for passenger and freight transport.
In addition, there will be four freight transfer yards and one container storage and loading yard at Chiang Khong Station, on an area of 150 rai, with a road link to the Chiang Khong border checkpoint.
Given the highlights of the new double-track Den Chai–Chiang Rai–Chiang Khong project, featuring Thailand’s longest railway tunnel and a future new tourism route, the State Railway of Thailand (SRT) has updated progress on all four tunnels as follows:
Tunnel 2 (Phrae Province), length 1,059 metres
- Cumulative planned progress: 83.30%
- Cumulative actual progress: 60.24% (behind plan by -23.06%)
Ngao Tunnel (Lampang Province), length 6,211 metres
- Cumulative planned progress: 70.80%
- Cumulative actual progress: 72.52% (ahead of plan by +1.72%)
Mae Ka Tunnel (Phayao Province), length 2,700 metres
- Cumulative planned progress: 64.02%
- Cumulative actual progress: 71.53% (ahead of plan by +7.51%)
Doi Luang Tunnel (Chiang Rai Province), length 3,400 metres
- Cumulative planned progress: 57.42%
- Cumulative actual progress: 67.17% (ahead of plan by +9.75%)
Meanwhile, as of January 2026, overall progress for the Den Chai–Chiang Rai–Chiang Khong railway construction project stands at 53.421%, against a cumulative plan of 53.641%, behind plan by -0.220%, broken down by contract as follows:
- Contract 1 (Den Chai–Ngao section): cumulative construction progress 51.530% (behind plan by -6.919%)
- Contract 2 (Ngao–Chiang Rai section): cumulative construction progress 58.857% (ahead of plan by +3.837%)
- Contract 3 (Chiang Rai–Chiang Khong section): cumulative construction progress 48.473% (ahead of plan by +3.331%)
