This International Standard specifies test methods for type approval testing of the overrun brakes on trailers. It should therefore be used in connection with the pertinent regulation.1) NOTES 1 In order to understand fully the requirements of this International Standard and to ensure that the test procedures are correctly applied, it is recommended that the regulation is studied before application of this International Standard. 2 Only SI units are used in this International Standard. These test methods apply to the type approval of categories O1 and O21) trailers with inertia brakes by testing on an inertia dynamometer. They relate to mechanically and hydraulically operated braking systems.