Despite the development of other propulsion systems, the internal combustion engines will continue to be an essential element of vehicle propulsion on the road, as the sole source of propulsion or in hybrid drives. The main challenge for the regulatory bodies is to find suitable strategies to ensure the lowest possible impact on the environment, for new and in use vehicles. This research gives an insight into the issue related to the disproportion of exhaust emissions of diesel-powered vehicles under the conditions of real, in use, vehicle operation with respect to the approved values. Emissions measurements were performed on 6 different passenger vehicles homologated according to Euro emission standards, with correct and faulty emission control systems. The results obtained show significant increases in defective vehicle's NOx emissions from 58.2% for Euro 5 vehicles to 78.2% for Euro 4 vehicles and increases of 86% and 227% respectively, compared to the approved values with Conformity Factor 2.1, CO emissions are increased in the fault case from 197% for Euro3 to 780% for Euro 5. A guideline is given for the emission control system with respect to its accuracy. The brief analysis of the hybrid powertrain was also elaborated as a future replacement for conventional ICE units, contributing greatly to a cleaner environment. The proposed novel hybrid energy management strategy which included only regenerative braking, has given a promising result; NOx emissions are reduced by 45%, consumption and CO2 emissions by 44% and CO emissions by 31%.