As three new subway lines were put into operation on Sunday, Beijing's urban rail transit network has expanded to a total length of 879 kilometers, making it the longest in China, authorities said.

"The newly opened subway lines are crucial for easing traffic congestion in the city's central area and supporting the development of places along their routes," said Wu Yulan, deputy director of the rail transit operation management bureau at the Beijing Municipal Commission of Transport.

The three new lines are the first phase of Line 3, connecting Dongsishitiao to Dongba North, Line 12, connecting Sijiqingqiao to Dongba North and the remaining section of the southern extension of the Changping Line. They contribute approximately 43 km to Beijing's urban rail transit network, according to the commission.

Since the opening of Beijing's first subway line - Line 1, on Oct 1, 1969, the city has developed the longest urban rail transit network in the country, operating 29 subway lines and 522 stations. The subway system plays a foundational, supportive and leading role in the capital's development, Wu said.

"The three new lines not only add new east-west routes in the city center but also connects several north-south lines, providing new public transportation options for residents living in areas such as Madian, Anzhen and Dongba," she added.