Runway incursions are a major factor in aviation safety.  While many things have been done to reduce the accident rate in General Aviation and the Air Carrier Industry, both sides of the aviation house are still experiencing far too many runway incursions.  This could be the result of "Read back - Hear back" issues, poor airport signage, pilot inattention/knowledge, expectation bias, or a combination of factors.  Runway safety is a major concern for all pilots and if you have been around aviation for a long period of time you have probably seen some close calls on the runways and taxiways, or even been involved in some yourself.