SHANGHAI: Construction crews are busy working on six rail lines measuring a combined 255 kilometers beneath Shanghai, promising to make this year an historic one for the city's public transportation sector.

Officials from the Shanghai Shentong Metro Corporation, the developer and operator of the city's metro system, said the company would complete and start operating three of the new metro new lines by the end of this year.

The construction push will mark the first time Shanghai has built three lines in a single year. These new lines will expand Shanghai's current 145-kilometer metro network to 230 kilometers, giving the city the country's largest subway network.

The Shentong officials also said the company would complete Line 4, a circular route which currently operates in a shape like the letter "C", by the end of this year.

In the past month, extensions of lines 2 and 3 were opened to passengers. The two stretches connect the city's centre to the Bao Steel Factory in Baoshan District and the planned Hongqiao Transportation Hub in Changning District.

The city's five existing lines served some 649 million passengers last year, with an estimated daily flow of 1.78 million, representing a 10 percent increase over 2005, according to Shentong.

Shanghai is expected to have a 400-kilometer subway network by 2010, when the city will host the World Expo. The expansion effort will give Shanghai the world's third biggest metro network and involve the relocation of more than 10,000 residents and 1,000 enterprises.

"The World Expo will help Shanghai speed up the construction of its public transportation infrastructure, especially subways, because the event is expected to draw a large number of visitors to the city," said Zheng Shiling, an architecture professor and the director of the Shanghai Urban Planning Commission.