A road when it’s dry, a river when it pours: How KL’s SMART Tunnel switches from highway to flood channel

KUALA LUMPUR, Oct 29 — The SMART Tunnel serves a dual purpose in Kuala Lumpur: it offers motorists a way to evade traffic congestion while also managing stormwater and preventing flooding. Spanning 9.7km, the tunnel combines a 3km motorway with a sophisticated flood-control system. This setup channels stormwater from the Klang-Ampang catchment area to reduce downstream flooding risks, including those near the confluence of the Klang and Gombak rivers.

The tunnel boasts a water-storage capacity of three million cubic meters and has logged 685 incidents of diverting water during heavy rains. The project, costing around RM1.93 billion, was conceived in 2001 to tackle Kuala Lumpur’s recurrent flooding and congestion issues. Developed by Gamuda Berhad in collaboration with engineering consultants and the Malaysian Highway Authority, the tunnel involved both public and private sectors.

Construction began in 2003, resulting in its opening to traffic in 2007. During heavy rainfall, the SMART Tunnel functions as a flood channel, diverting excess water into storage facilities. When it rains heavily, water is diverted through a lower channel beneath the motorway, while the motorway remains operational. However, when the flow exceeds 150 cubic metres per second, the motorway is closed and cleared for floodwater.

After the floodwaters are drained, the tunnel undergoes a six-stage recovery process before the motorway can reopen.