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Tehran MetroLine 3 travels from northeast to southwest. Line 3 is one of the most important lines as it connects southwest Tehran to northeast, crosses busy parts of the capital city, and can help to alleviate traffic problems. About 7 kilometers (4.3 mi) of Line 3 became operational in December 2012, followed by 12 kilometers (7.5 mi) in April 2014, and finally, the last section of the line which is 18 kilometers (11 mi) opened on September 22, 2015, increasing the length of the line to a total of 33.7 kilometers (20.9 mi).