AN AMERICAN expatriate was killed when his motorcycle went under the wheels of a China Motor Bus double-decker on Shek O Road near Lan Lai Wan early yesterday. Mr Allison Robert Mercer Jnr, 29, was travelling to Shek O when he was in an accident with a number nine bus being driven to Chai Wan. Mr Mercer, who lived in Shek O, was trapped under the bus before being freed. He was taken by ambulance to Tang Shui Kin Hospital in Causeway Bay, where he was later pronounced dead.