Beijing is mapping out a suburban railway network radiating from the capital's downtown area to boomtowns in suburban districts, the city's urban planner has said.

Five trunk lines and a lateral line have been under a feasibility study of the city's suburban railway construction plan, according to a report on the Beijing Municipal Commission of Urban Planning website.

"The total length of the railway track will add up to 360 km. They are to be open for traffic by 2020," the report noted.

In 2005, Beijing announced it would build 11 new suburban towns to divert the capital's growing population from its crowded core.

The 11 suburbs, featuring cheaper housing prices, convenient public services and a pleasant environment, are expected to absorb five to six million people by 2020. At the time, the city's population is predicted to hit 18 million.

The planned suburban railway lines are aimed to facilitate passenger flow between the city's core to the new suburban towns of Yanqing, Changping, Mentougou, Huairou, Miyun, Pinggu, Shunyi, Fangshan, Daxing, Yizhuang and Tongzhou.

The railways would be built on many sections of deserted tracks that were once used by factories to transport raw materials such as coal. However, many of those factories have been relocated further away from the city in effort to treat pollution, the commission said.

The railway lines allow for a speed of over 50 km per hour, double that of urban rail in the downtown area.