Automotive emission limitations and the means by which compliance with these limitations are verified directly influence engine design. The paper examines the optimization of these limitations and the verification procedures for Diesel engine operation.Emission testing is examined with concentration on various points: comparison of different national procedures, the effect of the total number of tests, the standardization of procedures for different vehicle types, and the suitability of steady-state tests for unsteady operation. Establishment of effective pollution limits deals with other questions: which emissions should be controlled, what criteria determine limiting values, do different criteria apply to different vehicle classes? Finally, a representative sampling of vehicles with Diesel engines are evaluated according to selected emission limits and a defined testing procedure; the effect of different Diesel engine designs on emissions are shown and various improvements are suggested, where necessary, to permit compliance with the emission regulations. Consequently, the regulations and testing procedure effectively establish design goals for engine development.