This International Standard specifies methods for testing the endurance braking systems of vehicles of categories M N and O (excluding M1, N1, O1 and O2) which are designed to comply with ECE-R 13/09 with supplement 1 to 6. The values given in square brackets are taken from ECE Regulation No. 13 for information. All endurance test procedures are based on the principle of equivalent energy absorption and procedures which are not suitable to support this principle are not considered. The principle of equivalent energy allows the base test parameters to be adapted to the variations occurring under real conditions compared to theoretical values. NOTE Typical sources are: ? The variation of the gradient of downhill test track or ? The variation of retarding force during drag tests or indoor test.