The $160 million Sentosa Gateway Tunnel, the construction of which was delayed for a year, could open as early as April and ease the congestion around the area.

The two-lane tunnel starts at the stretch between VivoCity and St James Power Station, and goes under Telok Blangah Road, before forking out into two single-lane roads - one to Lower Delta Road, and the other to Keppel Road.

It will allow motorists leaving Sentosa to bypass the busy junction at Sentosa Gateway and Telok Blangah Road, as well as one at Telok Blangah Road and Kampong Bahru Road. Traffic in the tunnel goes only one way.

The Land Transport Authority (LTA) had said previously that motorists who use the tunnel can halve their travel time. On the surface level, travel time will be cut by a quarter of the usual time taken. LTA said yesterday that it has completed the structural, electrical and mechanical works for the project, and is now in the final stages of work, such as road surfacing.The tunnel is scheduled for testing in the first quarter of this year, before it can be opened 'shortly thereafter', the LTA spokesman added. Tests include running through procedures for vehicle recovery, in the event of a breakdown, for example.

The project was announced in 2008 to cope with the expected increase in traffic with the launch of Resorts World Sentosa in 2010, and new residential and commercial developments on Sentosa. Work began in 2010 and was targeted to finish at the end of 2015. But the complexity of the construction forced the delay.

The road tunnel is located just 1.6 metres above the North-East Line MRT tunnels and about a metre away from the foundations of the West Coast Highway Viaduct. This meant having to take extra care that the surrounding structures were not affected by the tunnelling.

Micro boring machines - about eight times smaller than the regular boring machines used for MRT tunnelling - had to be used to progressively dig smaller tunnels to install steel pipes. These interlocking pipes would form the perimeter of a tunnel box. Excavation of the actual tunnel then took place in stages, and frames were installed to support the ground above as well as to minimise movement below. Concrete slabs were then cast to form the tunnel's structure.

Dentist Justin Ang, 41, who lives on Sentosa, said, "Traffic out of Sentosa can be slow-moving during the weekends, especially in the evenings. With the tunnel, I can bypass the traffic junctions and cut down my travel time to Lower Delta Road." Businessman Adrian Koh, 39, who shops at VivoCity, said, "When you exit the mall carpark and get onto Sentosa Gateway, it is usually quite congested. I have to wait for two to three traffic light cycles before I can clear the junction with Telok Blangah Road."