This International Standard is applicable to heavy-duty road vehicle engines subject to regulations as regards their exhaust emissions at the time of their certification.Mopeds,motorcycles,passenger cars and non-road vehicles are not within its scope.This International Standard defines the criteria making it possible to group those engines of the same manufacturer having,by design,similar regulated exhaust emission characteristics(gaseous and particulate pollutants,as well as smoke)within a family or families.It defines the parameters necessitating the carrying out of different groupings,leaving open to the manufacturer the latitude to carry out groupings of lower size.This International Standard defines the procedure for selecting from within each engine family the parent engine,the specific characteristics of which will probably make it more difficult to produce a low level of exhaust emissions.