Ngao Tunnel breakthrough nears Thailand's longest rail link

The Ngao Tunnel, set to be Thailand's longest railway tunnel at 6,215 metres, has been broken through in Lampang province, with only 24.30 metres of rock left to excavate. Khaosod English reported that Transport Minister Phiphat Ratchakitprakarn presided over the breakthrough ceremony in Ngao district on Wednesday, November 11, and that trains are scheduled to use the line in 2028.

Digging began on December 22, 2023. The State Railway of Thailand (SRT) expects the remaining excavation to finish in December, which would close the main phase of the tunnel's civil works.

What the Ngao Tunnel is part of

The tunnel sits on the Den Chai–Chiang Rai–Chiang Khong double-track railway, a new line of roughly 323 kilometres. According to Thai PBS and Bangkok Biz News, the route passes through four northern provinces: Phrae, Lampang, Phayao and Chiang Rai. It ends at Chiang Khong, a Thai–Lao border trading gateway on the Mekong.

The project is built in three construction contracts. As of October 2026, overall progress stood at about 74 percent, according to the SRT figures quoted by Thai media. The Den Chai–Ngao section was at roughly 76 percent, Ngao–Chiang Rai at about 75 percent and Chiang Rai–Chiang Khong at around 70 percent.

Why the engineering was difficult

SRT Governor Anan Phonimdaeng said crews had to bore through mountainous ground with complex geology. The rock includes thick limestone and volcanic ash deposits that formed hundreds of millions of years ago, which required specialised methods and close safety supervision.

To speed up the work, the railway authority used an adit, a side access tunnel 8.5 metres in diameter, near the middle of the route. It created two extra working faces, so crews could dig in several directions at once. Thai PBS reported that the southern section measures about 3,831 metres and the northern section about 2,384 metres.

What happens next

Once excavation ends, the work moves inside the tunnel. The sequence described by Khaosod English and Thai media is:

• building the internal structures of the tunnel;
• installing railway engineering systems and safety equipment;
• carrying out inspections and system testing before opening.

Mr Phiphat described the breakthrough as an engineering achievement and a step towards a wider network that links northern Thailand with its neighbours. Thai reports quote him as saying the new line could connect regional trade with neighbouring countries over time and reduce reliance on long-distance road freight.

Why it matters for travellers and trade

Rail passengers in the north currently have fewer options to reach Chiang Rai, which has no train station of its own. The new line is designed to change that, giving travellers a safer alternative to long bus or road journeys. For businesses, officials point to easier movement of agricultural goods, industrial products and cross-border cargo.

For readers who follow Thailand's transport build-out, our earlier coverage of Thailand's high-speed rail plans explains how the country wants to connect its cities. Our report on a train derailment in Prachuap Khiri Khan is a reminder of why rail safety matters, and the story on bus services changing amid rail expansion looks at how road operators are adapting.

The timeline still has hurdles. Most of the railway remains under construction, and the 2028 opening date depends on the remaining work across all three contracts finishing on schedule. Officials have said they will speed up the rest of the construction while keeping quality and safety standards strict.

For now, the breakthrough is a visible milestone for a project that has taken years to move from planning to construction. If the December excavation target is met, the focus will shift from digging to fitting out the tunnel for trains.

The original report was published by Khaosod English.

Image: Khun Tan Tunnel in northern Thailand, an existing railway tunnel shown for illustration; the Ngao Tunnel is the new, longer tunnel on the Den Chai–Chiang Rai line. Photo by Supanut Arunoprayote via Wikimedia Commons, CC BY 4.0.