In the past, the air-conditioned bus routes were numbered as 200's (Kowloon and New Territories) and 500's (Hong Kong Island).
However, this identification became void after they phased out all the non-aircon buses; since then, bus routes have used the old numbers.
There is one public light bus route operating in Airport/Lantau Island (901).
From c. 2003, the route numbers have been changed to prefixes "HR", "KR", and "NR".
There is no residential bus services on Lantau Island (except Discovery Bay) and the Airport.