This non-revenue connection tunnel was the means of supplying rolling stock to line M3 from 1976 until it was completed to Kőbánya-Kispest and the adjacent new depot in 1980.
The tunnel that connected line M3 to the outside world via a non-revenue connection function played a crucial role as a supply route for locomotives, operating from 1976 until its completion in 1980 when it linked to Kőbánya-Kispest and a new terminal.