People wait on a platform at the Dongsi Station of the newly-opened subway line 6 in Beijing, capital of China, on Dec 30, 2012. Beijing put four subway lines into operation on Sunday, part of the city's efforts to expand rail transit to ease severe traffic congestion. The new lines bring the number of subway lines in Beijing to 16, with a total length of 442 kilometers, according to authorities. [Photo/Xinhua]

BEIJING - Beijing put four new subway lines into operation on Sunday, increasing its daily passenger capacity by about 1.5 million.

The new lines have brought the number of subway lines in Beijing to 16, raising the national capital's total subway transport capacity to over 9 million passengers per day, said the Beijing Metro Company.

The total passenger transport capacity is expected to reach over 10 million on peak days.

At 442 kilometers, Beijing has the country's longest urban subway system.

The newly-opened lines include the new No. 6 Line, the southern section of the current No. 8 Line, the northern section of the current No. 9 Line and the southern and western stretches that complete a loop for the current No. 10 Line.

From 2013 to 2015, Beijing will put at least one new subway line into operation each year, according to the Beijing Metro Company.

By 2015, the number of subway lines in Beijing will reach 19, with a combined length of 561 km. By 2020, the total subway length is expected to increase to 1,000 km.