Shanghai, Dec 30 : Two new metro lines in Shanghai commenced operation on Thursday , which brings the total length of city's metro network to 831 km, solidifying its largest in the world status, according to authorities. The opening of the two new lines will bring the total number of fully automatic metro lines in Shanghai to five, with an operating length of 167 km, ranking first in the world for the first time, Xinhua news agency quoted the Shanghai Metro as saying. The newly opened Line 14 with an operating length of 38 km is the first fully automatic metro line for eight-carriage trains in Shanghai. With 31 stations, it is expected to serve as a horizontal artery in the metropolis. The northern part of the first phase of the newly opened Line 18 extends about 21 km with 18 stations. It is expected to significantly ease the traffic pressure in the downtown area. /IANS