Limit values for agricultural and forestry tractors and other off-road vehicle/machine engines are listed in tables 28 and 29 . Stage I ( table 28 ) is based on ECE regulation 96 ‟Uniform provisions concerning the approval of compression - ignition ( C.I . ) engines to be installed in agricultural and forestry tractors with regard to the emissions of pollutants by engine‟ and EU Directive 97/68/EC on the approximation of the laws of the Member States relating to the measures to be taken against the emission of gaseous and particulate pollutants from internal combustion engines to be installed in non-road mobile machines , which are identical .