The line is 22 km (14 mi) long with 19 stations and one terminal. Section 1, from Ferdowsi Square to Darvazeh Shemiran, opened in April 2008. Section 2 from Darvazeh shemiran to Shohada Square opened in February 2009. On May 24, 2009, Section 3 from Ferdowsi Square to Engelab Square opened. On July 23, 2012 two more stations were inaugurated, connecting line 4 with line 5. Currently there are 19 stations in operation on Line 4's trunk line, plus two more on the branch line serving Mehrabad Airport.