(43)The authorisation procedures for TSI conform and non-TSI conform vehicles are different. There may be cases where the choice of the procedure is not straightforward. Vehicles which come within the scope of TSI conform vehicles should be those vehicles where all the relevant TSIs have entered into force, including at least the TSI on rolling stock. This would mean that a significant part of the essential requirements has been laid down. For example, until such time that the conventional TSI on locomotives has entered into force, locomotives fall within scope of non-TSI conform vehicles, even though they might comply with other relevant TSIs in force at the time of their placing in service.