Establishes cabling specifications for an onboard data transmission bus between the different parts of equipment for service operations and monitoring of the fleet. Applies to equipment installed onboard buses, trolley buses and tramways as part of a bus fleet operation only; equipment includes operations aid systems, automatic passenger information systems, fare collection systems etc. Does not relate to the functioning of the vehicle, e.g. engine management, brake systems, driver dashboard ro or door opening systems. Not applicable to tramways operated as part of a train, metro or subway operation.