May 2007, after multiple delays. Meanwhile, the stormwater sections on the SMART system began operations at the end of January 2007. By 18 July 2010 the SMART system had prevented seven potentially disastrous flash floods in the city centre, having entered its first mode 3 operation only weeks after the opening of the motorway. As of September 2020, the tunnel had activated its fourth mode for the seventh time. During the flash flood on 10 September 2020, the tunnel diverted three million cubic metres of water. In December 2021, SMART entered Mode 4 for an eighth time, due to the massive flooding caused by heavy rainfall lasting from December 16 to 18. Things would have been much worse in Kuala Lumpur had it not been for the tunnel, which successfully diverted 5 million cubic metres of flood water during the 22 hours it was on full activation. Functioning The first mode, under normal conditions where there is no storm, no flood water will be diverted into the system. When the second mode is activated, flood water is diverted into the bypass tunnel underneath the motorway tunnel. The motorway section is still open to traffic at this stage. When the third mode is in operation, the motorway will be closed to all traffic. After making sure all vehicles have exited the motorway, automated water-tight gates will be opened to allow flood waters to pass through. After the flood has ended, the tunnel is verified and cleaned via pressure-washing, and the motorway will be reopened to traffic within 48 hours of closure. Technical specifications Stormwater tunnel Construction cost: RM1,887 million (US$514.6 million) Stormwater tunnel length: Diameter: 13.2 m (43.3 ft) (outer diameter) Tunnelling method: tunnel boring machine (TBM) TBM type: slurry shield Motorway tunnel Motorway tunnel length: Structure type: double deck Ingress and egress: at Jalan Sultan Ismail and Jalan Imbi Length: at Jalan Tun Razak Links: at Kuala Lumpur–Seremban Expressway Links: City Centre near Kg. Pandan Roundabout KL–Seremban Expressway near Sungai Besi Airport Features World's First Dual-Function Tunnel (Stormwater Management & Road) Longest tunnel in Malaysia 9.7 km (6.03 miles) stormwater by-pass tunnel 4 km (2.49 miles) double-deck motorway within stormwater tunnel The motorway tunnel is suitable for light vehicles only. Motorcycles and heavy vehicles are not allowed Ingress and egress connections to the motorway tunnel linking the southern gateway to the city centre Holding basin complete with diversion and tunnel