Complex sentence: All outbound journeys from the bus station to the airport are numbered A1 and go direct (via Temple Meads), thus a passenger going from Clifton to the airport gets on an inbound A2 which then becomes an outbound A1 upon reaching the bus station.
Split into simpler sentences: All outbound journeys from the bus station to the airport are numbered A1 and go direct (via Temple Meads). Thus a passenger going from Clifton to the airport gets on an inbound A2 which then becomes an outbound A1 upon reaching the bus station.