A long-running programme to double-track much of Thailand’s legacy metre-gauge network is making progress, with particular emphasis being placed on connectivity with neighbouring Laos. But perhaps more significant is that the enhancements will underpin a higher performing railway ahead of market liberalisation from 2028. Benjámin Zelki reports from Bangkok.
Double-tracking of the 144 km long metre-gauge line that links the key hubs of Nakhon Ratchasima and Kaeng Khoi in the centre of the country reached 95% completion in May. Works are expected to conclude next year, at which point the last section of single-track main line in the centre of the country will have been eliminated.
The work is the latest milestone in SRT’s ambitious but long-running programme to double-track its key cross-country corridors. This is augmenting the Bangkok – Nong Khai – Lao border high speed rail link, which is being built to 1 435 mm gauge rather than the 1 000 mm gauge used on most of the State Railway of Thailand network, with the exception of some corridors in Bangkok such as the Suvarnabhumi airport rail link. The first 250·8 km of new line between Bangkok and Nakhon Ratchasima section is now under construction.
While some piecemeal double-tracking had been undertaken by previous governments, a long-term programme was put in place in early 2018 when seven packages were approved totalling 993 km, worth approximately US$4bn.
This initial tranche of projects has now seen several sections of the network doubled, including some significant realignments to create a higher-capacity axis.
The corridor that links Chachoengsao and Laem Chabang, which lie east and southeast of Bangkok, and runs northwest to Phaknampho, is one example. Other routes where work has been finished include Nakhon Ratchasima to Khon Kaen in the northeast of the country, and the connection between Nakhon Pathom and Kaeng Khoi.
Rebuilding of the Nakhon Ratchasima – Kaeng Khoi route started back in 2018, but progress here has been especially challenging. Construction has been hampered by the mountainous terrain between Saraburi and Nakhon Ratchasima, requiring excavation of three new tunnels totalling 8 km, as well as several bridges and viaducts, and extensive earthworks.
Laos links make progress
Besides completing the central links, State Railway of Thailand is working to deliver three double-track corridors to the border with Laos, in addition to the proposed high speed line. Of these, two would be greenfield alignments, while one involves duplicating the existing railway.
The government approved the construction of the two new links totalling 678 route-km in early 2019. The first project to see work start is a 355 km line from Ban Phai on the existing network to Nakhon Phanom on the country’s eastern border. SRT reported in June that the project was approximately one-third complete, and the railway board approved a delivery deadline of November 2029 to reflect delays in land acquisition. The total project cost is estimated at 66·8bn baht.
The 177 km Ban Phai – Nong Phok section is being delivered by the AS-Ch Thavee & Associates joint venture, comprising A S Associate Engineering (1964), Ch Thavee Construction, the TBTC Joint Venture, Sermsanguan Construction and KS Joint Venture. Contractor for the remaining 175 km section from Nong Phok to Nakhon Phanom Friendship Bridge is the Unique Joint Venture comprising Unique Engineering & Construction, PCET, Thai Picon and Industry & Wacharakajorn.
Northern border link
The second new line could ultimately provide a connection into Laos from the northernmost tip of Thailand. This 323·1 km route leaves the existing network at Den Chai and runs north to Chiang Rai and Chiang Khong on the border. Civil works were reported to have reached 57% completion in May 2026, and works are expected to conclude in 2028.
This route includes several long tunnel sections in mountainous areas, constructed as twin single-track bores. The longest is the Ngao tunnel system, which consists of two parallel bores of approximately 6·2 km. The line will have 26 stations, four freight terminals and one container terminal and transhipment zone at Chiang Khong. The total project cost is estimated at 85·3bn baht.
Procurement of the civil works is split into three packages: the 104 km Den Chai – Ngao section is being built by the ITD-NWR joint venture of Italian-Thai Development and Nawarat Patanakarn, while the remainder of the route is being delivered by the same contractors under two separate work packages. The CKST-DC2 joint venture is managing the 132 km between Ngao and Chiang Rai, while the final 87 km to Chiang Khong is in the hands of CKST-DC 3. CKST-DC is made up of Ch Karnchang, Sino-Thai Engineering & Construction and Chiang Mai Construction.
Complex signalling picture
As well as the civil works needed to support what at some locations amounts to major realignment of the railway, the double-tracking programme also requires significant investment in signalling. This has been lent greater weight by the government and SRT seeking to ensure the main line network has modern ATP equipment installed as widely as possible.
Procurement of several signalling schemes is now either in progress or already complete. South Korea’s LS Electric is supplying computer-based interlocking systems for the 355 km Ban Phai – Nakhon Phanom line under a 32·7bn won signalling package awarded in 2024. It was also awarded a similar package for the 104 km Den Chai – Ngao section under a November 2022 contract worth a further 19·6bn won.
In November 2024, Hitachi Rail was awarded a framework covering the supply of ETCS Level 1 trackside equipment for the Den Chai – Ngao and Nong Waeng Rai – Nong Phok sections of the Ban Phai – Nakhon Phanom line. For the rest of the route to the border, Siemens Mobility is supplying the signalling under a December 2024 contract.
The company is delivering equipment, including centralised traffic control and ATP, complying with ETCS Level 1 standards. This includes the supplier’s Trackguard Westrace MKII interlocking, Controlguide Rail9000 CTC/LCP system, point machines, DC track circuits, and Clearguard ACM250 axle counters, with further components sourced locally. Most of the engineering work is being undertaken in Thailand, with support from Siemens Mobility’s sites in Spain, Australia and Germany.
The package for the 132 km Ngao – Chiang Rai section is valued at 26·9bn baht, while the 87 km Chiang Rai – Chiang Khong package costs 19·4bn baht.
System integration between the LS Electric and Siemens Mobility technologies was demonstrated on the SRT stand at the Asia Pacific Rail 2026 trade fair in Bangkok on May 6-7.
On to Vientiane
The third link to Laos focuses on doubling the existing north-south main line that runs for 167 km from Khon Kaen to Nong Khai on the border, 23 km south of Vientiane.
SRT signed a 28bn baht contract in December 2024 with the joint venture of Ch Thavee and AS Construction for civil works on the Khon Kaen – Udon Thani section. The Udon Thani – Nong Khai section is being delivered in smaller lots by several domestic civil engineering firms.
Under a November 2024 subcontract, Progress Rail is providing signalling and telecommunications systems for the whole route. The project includes the supply of computer-based interlocking, traffic management system and the installation of ETCS Level 1.
However, connectivity between Laos and Thailand remains a fraught topic. Currently, Thailand’s only rail access to Laos is the single metre-gauge track laid in the roadway of the 3·8 km Friendship Bridge across the Mekong River. A second bridge across the Mekong able to accommodate a standard gauge railway is planned, but the construction of this structure remains several years in the future.
Limited operation in the south
Meanwhile, SRT is making progress on providing a fully double-track alignment on the southern corridor linking the capital with Chumphon.
Doubling of the 421 km Nakhon Pathom – Chumphon line has been completed and SRT started operation on the second track in August 2024. The CS DCC Consortium, comprising Siemens Mobility, CRRC Dalian and China Railway Signal & Communication Corp was tasked with delivering the railway systems, although the signalling and telecommunications systems are not yet fully commissioned.
As a result, the line is operated under a transitional arrangement, SRT representatives explained to Railway Gazette International at Asia Pacific Rail. This provisional operation allows a limited throughput while the new control equipment is being commissioned progressively; bespoke train movement authorities are being issued on sections where the signalling is not yet fully cut over.
Next phases planned
Looking forward, further phases of the double-tracking programme remain on the national railway’s agenda. SRT has confirmed its plan to double a further 946 km of route, covering:
• Chumphon southwards to Surat Thani (168 km);
• Jira Junction (east of Nakhon Ratchasima) to Ubon Ratchathani (189 km);
• Phaknampho north to Den Chai (308 km);
• Den Chai – Chiang Mai (281 km).
SRT says completion of these later phases is expected after 2030.
Market opening ahead
Over the course of its life, the rationale for the investment in a double-track network has evolved beyond the immediate aim of enhancing operational capacity and resilience.
Now the programme is seen as integral to facilitating growth in rail traffic across the country, which the government hopes will be achieved by a set of reforms aimed at opening up the national rail network to competition.
A legislative package known as the Rail Transport Act BE 2568 came into force on March 27, paving the way for new entrants to start operations by 2028.
The provisions of the act will see SRT remain as the infrastructure owner, and it will retain rights to continue its existing passenger and freight services. However, it will be expected to make train paths available to private operators who can bid to operate new services. A Network Statement was published on June 26, providing information to aspiring new entrants about the state of the network and the future access conditions.
A track access charging structure has beenannounced, with tariffs set at an initial 44 baht per vehicle-km for regular passenger services, rising to 77 baht for tourist trains. Freight trains are to be charged 0·2065 baht per tonne-km.
To further accelerate the growth agenda, the government plans to invest more in rolling stock and the Thai supply chain. The national Rail Technology Research & Development Agency has already set out its plans to develop a domestic diesel-electric multiple-unit in partnership with the Department of Rail Transport and SRT.
Meanwhile, a prototype domestically developed luxury passenger coach has been presented in Bangkok.
This article first appeared in the August 2026 issue of Railway Gazette International
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Facts Only
* Double-tracking of a 144 km metre-gauge line linking Nakhon Ratchasima and Kaeng Khoi reached 95% completion in May.
* The work on this line is expected to conclude next year, eliminating the last section of single-track in that central area.
* This work augments the Bangkok–Nong Khai–Lao border high-speed rail link by transitioning it from 1000 mm gauge to 1435 mm gauge.
* The programme involves seven packages totalling 993 km, valued at approximately US$4 billion, initiated in early 2018.
* The initial tranche of projects included realignments to create a higher-capacity axis.
* Corridors completed include Chachoengsao–Laem Chabang, Nakhon Ratchasima–Khon Kaen, and Nakhon Pathom–Kaeng Khoi.
* Rebuilding the Nakhon Ratchasima–Kaeng Khoi route required excavation of 8 km of tunnels due to mountainous terrain.
* Three double-track corridors to Laos are being developed, including two greenfield alignments and one duplication project.
* A 355 km line from Ban Phai to Nakhon Phanom is one project underway for the Lao border link, with a delivery deadline of November 2029.
* A second northern border link is planned over 323.1 km, reaching Chiang Rai and Chiang Khong, with civil works at 57% completion as of May 2026.
* Southward corridor doubling of the 421 km Nakhon Pathom–Chumphon line is complete, with operation on the second track starting in August 2024.
* Future phases include doubling an additional 946 km of route, expected to be completed after 2030.
* Signalling procurement includes South Korea's LS Electric supplying systems for several sections and Hitachi Rail awarding a framework for ETCS Level 1 equipment.
Executive Summary
Thailand is advancing a program to double-track parts of its legacy metre-gauge railway network, with a focus on improving connectivity with Laos. Progress includes completing the double-tracking of a 144 km line linking Nakhon Ratchasima and Kaeng Khoi, which reached 95% completion in May and is expected to finish next year. This effort supports a higher-performing railway ahead of market liberalization scheduled for 2028. The work involves augmenting the Bangkok–Nong Khai–Lao border high-speed rail link by transitioning some sections from 1000 mm gauge to 1435 mm gauge, excluding specific links like the Suvarnabhumi airport rail link.
The overall program involves a long-term strategy initiated in early 2018, approved through seven packages totaling 993 km and an estimated cost of US$4 billion. Completed sections include corridors linking Chachoengsao and Laem Chabang, Nakhon Ratchasima to Khon Kaen, and Nakhon Pathom to Kaeng Khoi. Progress on the Nakhon Ratchasima–Kaeng Khoi route faced challenges due to mountainous terrain requiring tunnel excavation.
Significant work is underway on three corridors connecting to Laos. Two of these are planned as greenfield alignments, while one involves duplicating existing lines. A project covering 678 route-km was approved in early 2019 for the new links. The northern border link aims to provide access to Laos from the northernmost tip of Thailand over a 323.1 km route, involving long tunnels and infrastructure development across mountainous areas.
In parallel, work on the southern corridor connecting Bangkok with Chumphon is progressing; the double-tracking of the 421 km Nakhon Pathom–Chumphon line is complete, with operation starting on the second track in August 2024 under a transitional arrangement. The plan extends to double-tracking an additional 946 km, scheduled for completion after 2030. Furthermore, investment is being directed toward signalling upgrades using systems like ETCS Level 1, with contracts involving international suppliers like South Korea's LS Electric and Hitachi Rail.
Full Take
The narrative presents a layered strategy where physical infrastructure development is intentionally sequenced to precede market liberalization, suggesting that operational capacity enhancement is the necessary precondition for economic growth. The focus on multilateral links with Laos introduces an element of geopolitical linkage into domestic railway reform, raising questions about the prioritization of international connectivity versus internal national cohesion in resource allocation.
The complexity arises from the shift in gauge (from 1000 mm to 1435 mm) and the integration of diverse civil engineering challenges, such as tunneling through mountainous terrain. This demonstrates that modernization is not a linear process but a multi-faceted negotiation between physical constraints and strategic goals. The involvement of international technology providers for signalling underscores a systemic dependency where national progress relies on external technological frameworks.
The transition to private operation, facilitated by the Rail Transport Act BE 2568, establishes a framework for competition while retaining state ownership of infrastructure. The introduction of track access charging structures reflects a calculated move to monetize the network's utilization, creating a tension between public service obligations and commercial viability. The pattern observed is that large-scale infrastructural projects often serve as mechanisms to reallocate power and establish new hierarchies of economic influence, even when framed as purely technical modernization.
What factors determine which corridors receive priority in this phased development? How does the balancing act between domestic connectivity enhancement (like the southern link) and international access (the Laos links) affect long-term national strategy? If infrastructure serves to open markets, what alternative mechanisms exist for fostering equitable growth outside of direct commercial competition on existing lines?