BEIJING, Jan. 24-- Beijing plans to start construction on four subway lines in 2015 as the city authorities continue to resort to the metro system to ease traffic jams.

Beijing mayor Wang Anshun revealed the plan in the government work report he delivered to the annual meeting of the municipal legislature on Friday.

Officials with the Beijing Infrastructure Investment Co., Ltd. said the public-private-partnership (PPP) funding model might be used for the construction in a bid to reduce government debts.

Meanwhile, sections of two existing metro lines will be opened for riders this year, said Wang.

On Dec. 28, Beijing opened four new subway lines, increasing the total subway length in the Chinese capital by 62 kilometers to 527 kilometers.

Also on Dec. 28, the city authorities hiked the subway fares. While passengers used to be charged a flat fee of 2 yuan, they are now charged a minimum of 3 yuan for up to six kilometers and the price increases depending on travel distances.

The city's subway system carries approximately 10 million passengers daily on workdays. By 2020, the total subway length is expected to increase to 1,000 kilometers.