It looks like Big Bridge -- and there was a Big Bridge between Rathfarnham and Dublin at one time - destroyed in 1754. However it is probable that the area around it may have retained that name locally.
Wikipedia;-
This article lists the bridges and tunnels in Dublin and the Greater Dublin Area in Ireland. ... Pearse Bridge, Rathfarnham Road - R114, First bridge (called Big Bridge) destroyed by a flood in 1754, a new bridge was constructed in 1765.