The Land Transport Authority of Singapore has started the construction of its first undersea road tunnel project.

The 5km-long Marina Coastal Expressway (MCE) will cost more than (Singapore) $4.1bn.

MCE will serve the projected increase in future traffic at the new Downtown at Marina Bay, linking Kallang-Paya Lebar expressway and Ayer Rajah expressway.

The project faces new engineering and technical challenges, especially the 420m section of the tunnel that has to be constructed below the sea.

Land Transport Authority chief executive Yam Ah Mee said the team has successfully “moved” a river to build the KPE and will now dam the sea.

“Despite the challenges, we are very excited about this important project, which would support the long term growth of Singapore,” Ah Mee said.

The work for the undersea tunnel will be conducted in two stages without disrupting day-to-day operations of the Marina Barrage.

The project is scheduled to be complete by 2013.