Tehran Metro Line 1, coloured red on system maps, runs north–south and is 86.9 kilometers (54.0 mi) of which 14.9 km (9.3 mi) is underground (from Tajrish station to Shush Station) and the rest at grade (at surface level).

As of 2005[update], the line's total capacity is 650,000 passengers per day and trains make a scheduled stop of 20 seconds per station.

The trains are made up of seven wagons, giving a nominal capacity of 1,300 seated and standing passengers.

It also faced major financing issues as the government refused to release funds earmarked for the project to the municipality.

[3] With the inauguration of the 19 km (12 mi) long phase 3, the extension to Parand in December 2023, this whole airport branch was renumbered to line 1 again.