Many technological developments in automobile powertrains have been implemented in order to increase efficiency and comply with emission regulations. Although most of these technologies show promising results in official fuel economy tests, their benefits in real driving conditions and real driving emissions can vary significantly, since driving profiles of many drivers are different than the official driving cycles. Therefore, it is important to assess these technologies under different driving conditions and this paper aims to offer an overall perspective, with a numerical study in simulations. The simulations are carried out on a compact passenger car model with eight powertrain configurations including: a naturally aspirated spark ignition engine, a start-stop system, a downsized engine with a turbocharger, a Miller cycle engine, cylinder deactivation, turbocharged downsized Miller engine, a parallel hybrid electric vehicle powertrain and an electric vehicle powertrain. These are tested in seven driving cycles including the NYCC, FTP75, NEDC, WLTC, US06, HWFET and CADC. The impacts of different technologies on fuel economy and CO₂ emissions are analyzed, with respect to different operating conditions. Results reveal that a combination of certain driving cycles and vehicle configurations have a large influence on fuel consumption and CO₂ emissions. In general, Miller and downsized engines offer some improvements in all cycles while the start-stop system has benefits in city cycles with frequent stops. The HEV and EV configurations offer a substantial improvement compared to conventional technologies in lower speed conditions like city cycles, but their benefits are reduced at cycles including higher speeds.