The branched access system was constructed in 17 sections starting from the Paul Löbe House. Two of the sections, where the system crosses the Spree, are under the river. The emplacement of these two sections was a complicated process. The tunnel sections connecting all the buildings, except the Reichstag, to the access system are fitted with heavy watertight doors so that the buildings can be sealed off against flooding in the case of a disaster.

Three 12 tons heavy bulkheads protect the access system against possible intrusion of water

The circular at the loading ramp
of the Reichstag

Each building which is connected to the access system has its own access point with loading/unloading bays for goods vehicles. The Reichstag has its own roundabout for turning vehicles round.

The roadway at the exit to the Marie Elisabeth Lüders House 

The underground access route is a two-lane roadway 6.5 meters wide. On one side is a narrow foot-walk. For safety reasons there is a parallel pedestrian tunnel, for use in emergencies, which allows access to the buildings on the system or egress to the Spreeside through emergency exits.

Cables and supply lines run in a narrow horizontal shaft parallel to a wider shaft for ventilation, smoke removal, and the sprinkler supply system above the pedestrian emergency tunnel.

In order to ensure that an adequate flow of goods and supplies can be maintained, during the last stages of the planning of the of the 400 meter long underground access system, it was decided that the tunnel should have a height of around 4 meters, a road 6.5 meters wide and a total width of 8 meters.