Singapore is one of the most vibrant and colourful cities on the planet. And one of the busiest. With a permanent population of 4.5 million and a further 10 million visitors a year, the streets daily swarm with people, the roads are choked with cars, buses and bicycles and the trains are packed. Gridlock beckons.

In a bid to avoid transport meltdown, the government has embarked on a multi-billion-dollar project to construct the most sophisticated underground railway in the world. The project is hugely challenging. A complete, circular tunnel must be excavated beneath the city, while allowing life above to continue with minimum disruption.

When it opens some time after 2010, the new Central Circle Line will be 33.3km long and will have 29 stations. It will connect all the radial lines leading in and out of the city. Using the latest tunnel construction methods, the engineers must ensure that they avoid existing underground infrastructure such as the city’s deep tunnel sewerage system and the electricity network.

The Central Circle Line will be the latest addition to Singapore’s famous Mass Rapid Transit (MRT) network, the backbone of the railway system in Singapore, which carries some 1.3 million people daily. The initial section was opened in 1987, making it the second oldest metro system in southeast Asia after Manila’s Light Rapid Transport network.

The world’s first urban underground passenger-carrying railway started running between Paddington and Farringdon in London in 1863, and was the forerunner to the London Underground. The London Underground now has 274 stations, is more than 400km long and carries more than 2.7 million passengers a day.