A bicyclist was killed in a collision with a city of Santa Clarita Transit bus in Castaic early Wednesday morning, according to an official with the California Highway Patrol Newhall-area Office.  The man was approximately 57 years old, according to Officer Carlos Burgos-Lopez, spokesman for the CHP.  The initial call came in at 7:34 a.m. reporting a collision of a pedestrian and a school bus at the intersection of Green Hill Drive