SMART Tunnel is a subterranean vehicular and stormwater tunnel in downtown Kuala Lumpur. The name is an acronym for Stormwater Management And Road Tunnel. The tunnel comprises a motorway tunnel with a bypass flood water tunnel underneath it. When there is no flood, the motorway tunnel is open to traffic, but when there is a stop, the bypass flood water tunnel is activated, and the motorway tunnel is closed to traffic. Once all vehicles have exited the tunnel, the flood gates are open to allow flood water into the bypass tunnel. Once the water has flowed through, the flood gates are closed and the motorway tunnel reopened to traffic.
The SMART Tunnel was built at a cost of RM1.887 billion, it has a length of 9.7 km (6 miles). Of this, the motorway tunnel is just 4 km (2.49 miles). Nevertheless, upon its completion, it still became the longest road tunnel in the country after the Genting Sempah Tunnel. The motorway tunnel carries a Malaysian expressway code of E38. The tunnel accepts entries by private cars and taxis only. The toll is RM3 per vehicle paid upon entry using Touch 'n Go and SmartTAG.