CHANGSHA, March 20 (Xinhua) -- A three-tower cable-stayed heavy railway bridge closed Sunday over Dongting Lake, the second-largest freshwater lake in China.

The 1,290-meter bridge is designed with a carrying load of 10,000 tonnes, enough to accommodate a fully-loaded train passing at a speed of 120 km per hour.

Xu Bin, project manager of China Railway Major Bridge Engineering Group Co. Ltd., said the Dongting Lake Bridge is the world's longest three-tower cable-stayed railway bridge. It is also the first time steel box girders have been used for such a bridge.

The bridge is an important part of the world's longest heavy-duty railway for coal transport. The 1,814.5-km railway is still under construction and is designed to link the coal-rich western Inner Mongolia Autonomous Region with Ji'an City in east China's Jiangxi Province.

The railway line is scheduled for operation in 2020 with an estimated investment of 193 billion yuan (28 billion U.S. dollars). It is expected to be a trunk energy supply channel, linking north and west China's energy suppliers with economic powerhouses in the middle and lower reaches of the Yangtze River. It is designed with an annual transport capacity of over 200 million tonnes.