Thailand’s first expressway tunnel proposed through 36 billion baht investment

The Expressway Authority of Thailand (EXAT) has put forth a proposal for an underground expressway, aiming to replace a contentious section of the N1 Expressway development. The proposal came after an extensive 17-month initial feasibility study.

EXAT Governor Surachet Laophulsuk revealed this plan during the project’s second hearing, stating that multiple factors such as engineering, investment costs, and environmental impact, were thoroughly evaluated. The result revealed that an underpass was the most viable option.

This proposed 6.7 kilometre underpass would be Thailand’s maiden expressway tunnel. It would stretch along Ngarmwongwan Road via Phongphet Intersection, Bang Khen Intersection, and Kaset Intersection to Prasertmanukit Road, before connecting with the N2 Expressway.

Surachet explained that among the three options studied, the tunnel scored the highest, with a total score of 82.5. The estimated investment cost for this project is 36 billion baht, and it’s expected to generate an economic internal return rate of 17%.

He further assured that EXAT is financially sound and considering investing in the project itself. If necessary, the agency might contemplate issuing bonds to procure funds for the construction.

The environmental impact assessment, according to Surachet, is due for completion in May next year and will be submitted to the cabinet for approval. The bidding process is tentatively set for 2026, and construction is expected to commence the following year.

With construction estimated to take about five years, the anticipated traffic volume upon the first year of opening is 70,000 vehicles per day. This volume is half of the route’s total capacity.

Surachet expressed confidence that the proposed underpass would be accepted by those who had previously raised environmental concerns about the design.

Surachet also shed light on the three-phase expressway development’s northern part, which is divided into two stages. The initial stage, N2, extends from Prasertmanukit Road to the eastern Outer Ring Road, covering a distance of 11.3 km and requiring an investment of 16.9 billion baht. This project is now ready and will be submitted to the new government for approval shortly.

For the second stage, N1, EXAT has conducted a feasibility study to identify alternative routes that could replace the controversial section. Following discussions with Kasetsart University and communities along the planned route, the underpass was conceived as the most suitable alternative, reported Bangkok Post.

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