Yes, there are roads on military based that are open to the public but this is the exception rather than the norm. Garrison commanders can raise the FPCON at any time and limit the accessibility of the base (in areas behind the gates).

What I don't want to see is you (or anyone) make general edits to military installations without checking conditions. There have been a number of DWG cases lately where people make edits to bases over access, only to be reverted. Their reasoning is around being unable to route their [insert delivery app name] there. That is a software problem however. Routers can permit access over private routes if the developer desires to allow this.