A 30-year-old Janesville man is dead after the motorcycle he was riding collided with a semi.  The Rock County Sheriff’s Office says the crash happened Friday evening in the 12700 block of East US Highway 59 in Lima Township.  An investigation finds the motorcyclist was trying to pass multiple cars and a semi-tractor with a trailer.  According to the sheriff’s office, the motorcyclist saw an oncoming car, tried to avoid it by shifting lanes, and then struck the rear driver’s side of the semi, which was driven by a 34-year-old Whitewater man.  The cyclist was pronouced dead at the scene. His name has not yet been released by authorities.  Highway 59 was closed at Salisbury Road for nearly two hours due to the crash.