For the record, my question is not about mistakenly using a taxiway as a runway.
I've noticed recent changes to the sectional and TAC VFR maps around Metropolitan Oakland International Airport (OAK/KOAK) - it appears that Taxiway W is being "promoted" to a runway close to, and parallel to, Runway 12/30.
Based on the airport map (PDF) and confirmed by the Google Earth image below, aircraft departing and landing on 12/30 (presumably soon-to-be 12R/30L) will have to taxi up or down this new runway. From the looks of it, this runway will just be marginally long enough (about 7200 ft / 2195 m) to handle short-range commercial operations; certainly the longer runway will still need to be used.
This then begs the question: How would airport operations be affected if both runways were active?