该程序包括从以下方面估算特定车辆的总减速能力:a）自然减速（滚动阻力、空气动力阻力等）；b） 发动机阻力；和c）发动机、整体式自动变速器、动力传动系或拖车轴减速器。它假定基础制动器不用于在长下坡时保持速度。减速是根据最大等级评定的，在该等级上，每个档位可以在适合该档位的公路速度范围内保持稳定的控制速度。对于每个档位，计算程序确定至少四个控制速度值的最大等级，范围从对应于满载调节发动机转速的车速到对应于最小（怠速）转速下发动机转速的车速。 此外，计算程序还提供了每个档位的总减速功率信息。本程序提供了一种统一的方法，用于计算和报告在下坡行驶的重型卡车和公共汽车所使用的发动机、整体式自动变速器、动力传动系或拖车轴减速器可维持的稳态控制速度。它提供了一种实用的方法，可以使用描述缓速器性能特征的数据和其他车辆设计变量来预测特定车辆安装中的缓速器性能。它旨在通过将规定的减速器性能与特定车辆功能要求相匹配，帮助正确选择减速器。

The procedure covers the estimation of the total retardation capability available to a specific vehicle from: a) natural retardation (rolling resistance, aerodynamic drag, etc); b) engine drag; and c) engine, integral automatic transmission, driveline or trailer-axle retarders. It assumes that foundations brakes are not used for maintaining speed on long mountain descents. Retardation is rated in terms of the maximum grades on which stable control speeds can be maintained for each gear over the range of highway speeds appropriate to that gear. For each gear, the calculation procedure determines maximum grades for at least four values of control speed ranging from the vehicle velocity corresponding to full load governed engine rpm, to the vehicle velocity corresponding to the engine rpm at minimum (idle) speed. in addition, the calculation procedure provides information on the total retarding power available for each gear.This procedure provides a uniform method for calculating and reporting the steady state control speed maintainable by either engine, integral automatic transmission, driveline, or trailer-axle retarders employed by heavy trucks and buses operating on downgrades. It provides a practical method of predicting retarder performance in a specified vehicle installation using data describing retarder performance characteristics and other vehicle design variables. It is intended to assist in the proper selection of a retarder by matching stated retarder performance capabilities with particular vehicle functioning requirements.