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internal view of tunnel lining under construction

SMART, Malaysia

SMART – Stormwater Management and Road Tunnel – is as clever as its name suggests. The world-first dual-purpose tunnel diverts flood waters away from the confluence of the two rivers running through central Kuala Lumpur while its middle section doubles up as a two-deck motorway to relieve traffic congestion at the main southern gateway into the city center.

Shot of giant tunnel boring machine dwarfing workers standing in front of it.

SMART's outstanding performance won it the Road Engineering Association of Malaysia’s Award for Road Engineering Excellence.


Ever since widespread floods hit the capital in 1971, the government of Malaysia has implemented measures to increase the rivers’ capacity for coping with flood waters from upstream.

But over time, conventional methods such as channel widening and deepening had become inadequate and urban development was making matters worse. Detailed studies led to the concept of a tunnel for stormwater storage, and then at design stage came the novel idea of using it to tackle traffic congestion.


After approval by Malaysia’s government, development began by the MMC Engineering-Gamuda joint venture, with engineering support from SSP Consultants and Mott MacDonald.

Our team designed the tunnels and underground structures, the hydraulics and stormwater control systems, and the road tunnel ventilation, lighting, and communications systems. The tunnel is 7 miles (11.5 kilometers) long and 43 feet (13.2 meters) in diameter.

SMART’s major components include an upstream intake structure, holding pond and storage reservoir, diversion tunnel, twin box culvert and ingress/egress connectors to the motorway tunnel. Ground conditions dictated construction by tunnel boring machine (TBM), with two state-of-the-art slurry TBMs working in opposite directions from the middle of the tunnel alignment.


SMART works on a three-mode system. Mode one operates under normal conditions or when rainfall is low enough that no water needs to be diverted into the tunnel. Moderate storms activate mode two. This diverts flood water into a bypass tunnel in the lower section of the motorway tunnel, which remains open to traffic.

During the once- or twice-yearly heavy storms, a switch is made to mode three, when the tunnel is closed and the full tunnel section with a combined capacity of 106 million cubic feet (3 million cubic meters) becomes available to divert the dramatically increased flows. Extensive monitoring stations ensure sufficient time is allocated to allow the last vehicle to exit before the automated water-tight gates open.

The motorway reopens to traffic within 48 hours of closure. We helped ensure that operational aspects of the change over between modes from vehicle to flood use are efficient.

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