CENTER CITY (WPVI) -- A 27-year-old man was killed while operating a motorcycle. Police say he was doing wheel stands at the time of the crash in Center City, Philadelphia.The crash happened around 3 p.m. Saturday at 17th and Ben Franklin Parkway.Police say the motorcycle collided with a box truck.The victim was taken to Hahnemann University Hospital, but died from his injuries.The accident remains under investigation.----------