Access tunnel

Access tunnels or access conduits were tunnels used for accessing various systems and portions of space-borne stations. Access tunnels are used by the Tyrans and Cardassians. The Federation equivalent of the access tunnel is the Jefferies tube. 

Background
The restricted area access tunnel that Rom accesses in "Behind the Lines" has the statement 'A51', which could be an in-joke for Area 51.

Wartungsschacht