Malaysia today unveiled the world's first dual function road and stormwater tunnel in an expensive bid to alleviate flash floods and ease traffic congestion at peak hours.

The Smart (Stormwater Management and Road Tunnel) motorway, built at a cost of RM1.9 billion, serves as a stormwater duct and road highway, Bernama news agency reported.

Works Minister S Samy Vellu was quoted as saying that the four kilometre motorway, which opened to motorists on Monday, will be toll-free for one month but added that rates had yet to be determined.

"Taking into consideration the amount of time spent and cost to build this tunnel, we should not come to think that the toll rate will be similar to the one imposed on ordinary highways. It will be higher," Samy Vellu said.

The double-decked motorway tunnel is a speedy alternative route to and out of Kuala Lumpur, which has a heavy concentration of offices in its centre, causing massive bumper-to-bumper traffic jams during peak hours.

Construction on the project began in 2003. While cars will start plying the Smart motorway from Monday, the stormwater channel - a 9.7 kilometre stretch which runs underneath the road - will be operational in June.

Samy Vellu also said that the government will consider building more motorway tunnels to help ease traffic jams in cities and prevent landslides on roads in hilly areas.