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

The SMART Tunnel in Kuala Lumpur serves a dual purpose as both a motorway and a flood-control system. Stretching 9.7 kilometers, the tunnel combines a 3-kilometer double-deck road with flood-control infrastructure designed to divert excess water away from the city center during heavy rain. The SMART Tunnel's primary function is to channel water from the Klang-Ampang catchment area to reduce downstream flood risks, particularly around the confluence of the Klang and Gombak rivers near Masjid Jamek.

The project, costing around RM1.93 billion, emerged as a response to Kuala Lumpur's recurring flooding problems. Its development involved both government and private sector collaboration, with the government commissioning the stormwater management aspect and private companies handling the motorway construction and operation under a Build-Operate-Transfer (BOT) model. The project involved various agencies, including the Department of Irrigation and Drainage (DID) and the Malaysian Highway Authority.

The tunnel operates in four distinct modes. Mode 1 is normal operation, where traffic uses the motorway as usual. Mode 2 activates when water levels rise, diverting excess water through the lower channel beneath the motorway, while maintaining traffic flow. Mode 3 involves closing the motorway and clearing it of vehicles in preparation for potential floodwater diversion.

Mode 4 is a prolonged severe storm scenario, where the motorway compartments are used to carry floodwater after all vehicles have been evacuated. The distinction between Modes 3 and 4 is crucial, as the motorway may not necessarily be flooded in Mode 3 but could be utilized for floodwater channeling in Mode 4.