This paper describes the bus audience model created by The MVA Consultancy to provide audience measurement of advertising on London's buses. The model was successfully launched in 1991 with the approval of JICPAR (Joint Industry Committee for Poster Audience Research) and has undergone close scrutiny by the advertising industry. BUSADS - Bus Audience Data System - is comprised of three databases: bus network database; home interview survey; car video survey; which are combined to provide both pedestrian and vehicular audiences of bus advertising campaigns. Since 1991 BUSADS has been subsequently updated and enhanced. It now offers audience measurement of 13 different site types; pedestrian and vehicular audience for inner/outer London campaigns; audience sensitive to hours of daylight; audience segmentation by up to 200 lifestyle variables; London population and London TV area audience estimates.