Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Communication Breakdown
ATC Issue All Types; Conflict Ground Conflict; Less Severe
Flight Crew Executed Go Around / Missed Approach; Flight Crew Requested ATC Assistance / Clarification
Airport
On approach to runway 27R in PHL after clearance to land an aircraft crossed the runway in front of us.  There was no call from the tower about this aircraft crossing; and we heard no call from the tower telling this aircraft to cross.  As we continued another aircraft stopped short of the runway; then on a short final the aircraft holding short of the runway started to roll onto the runway at the rate the aircraft was rolling we would either be in the flare or on the ground before the aircraft cleared.  I called a go around.  When I called the go around to the tower they told us the traffic was in taxiway Y.  This taxiway is just beyond the end of runway 27R and at the altitude we were when the aircraft crossed there would be no way of us telling that this aircraft was not crossing on the runway unless notified by the tower.
Captain of a medium sized turbojet reported that the proximity and arrangement of a taxiway makes it appear as if taxiing traffic is on runway 27R.