Service connecting branches of 2/5 Lines
The longest connecting tunnel in the Saint-Petersburg metro is also the most frequently used for passenger traffic.
If you go along 5th Purple Line from the station СадоваяRU to the station АдмиралтейскаяRU, then immediately behind the station СадоваяRU you can see the track development - the branches from both tunnels converge together into the central tunnel. This is the beginning of the connecting tunnel, before the opening of the section to the station Старая ДеревняRU it was also used as a reverse exit:
Interestingly, at least one vent in this connecting tunnel is a full-length tunnel without rails. In addition to the many advanced ventilation and drainage devices, the connecting tunnel itself is very long and has many traffic lights, like in "real" working tunnels.
There is also its own hermetic door. This is serious. The connecting tunnel ends at the approach to the station Невский ПроспектRU with the usual train maintenance point: