<div class="section abstract"><div class="htmlview paragraph">The latest legislative tendencies for on-highway heavy duty vehicles in the United States such as the feasibility assessment of low NO<sub>X</sub> standards of CARB or EPA’s memorandum forecast further tightening of the NO<sub>X</sub> emissions limits. In addition, the GHG Phase 2 legislation and also phased-in regulations in the EU enforce a continuous reduction in CO<sub>2</sub> emissions resp. fuel consumption. In order to meet such low NO<sub>X</sub> emission limits, a rapid heat-up of the exhaust after-treatment system (EATS) is inevitable. However, the required thermal management results in increased fuel consumption, i.e. CO<sub>2</sub> emissions as shown in numerous previous works also by the authors. A NO<sub>X</sub>-CO<sub>2</sub> trade-off for cumulative cycle emissions can be observed, which can be optimized by using more advance technologies on the engine and/or on the EATS side.</div><div class="htmlview paragraph">In the present study a systematic investigation is carried out by means of model-based holistic approach targeting the definition of a high efficiency engine layout and optimal thermal management calibration. First, the potentials of combustion process optimization (compression ratio, peak firing pressure) and of turbocharger efficiency increase are quantified aiming engine efficiency increase. Afterwards, using holistic engine and EAT concept development approach, conventional and advanced EATS layouts are tested. The advanced EATS layout consist of a close-coupled dual-stage SCR system. In order to explore the benefits of each layouts, the engine heat-up calibrations are varied and the resulting, cumulative NO<sub>X</sub>-CO<sub>2</sub> emissions of the investigated cycle are compared and evaluated. Multiple improvement measures for both engine and EAT system are discussed and an outlook of future powertrain concepts is given.</div></div>