after the change of route of national route 9, in the late 1950s, the section from avenida general paz and campana was changed to rn12. in 2005 the 8 km section between national route 9 in campana and the bartolomé mitre bridge access over the paraná de las palmas river changed to buenos aires provincial jurisdiction as a new section of provincial route 6. rn12 runs over the ol roadbed of national route 193 to the bridge over national route 9 in zárate.