A head-on collision yesterday on Piilani Highway near Wailea on Maui sent three people to a trauma center - two with life-threatening injuries.  It happened just before 4:30 p.m. when a Honda Civic, driven by a 64-year-old woman was traveling north, crossed over the centerline and collided head on with a Toyota Corolla traveling south. A 50-year-old Kahului woman who was a passenger in the Honda suffered life-threatening injuries.  The driver of the Toyota, a 48-year-old Kahului man, also suffered life-threatening injuries. The driver of the Honda was also injured.