The evolution of medium and heavy duty trucks and buses has been driven by market and regulatory demands. Over the years, criteria pollutant reductions have been realized with improvements in engine design and advanced after treatment systems. More recently the interest in reducing greenhouse gas emissions has driven the development of hybrid powertrains for these applications. Hybridization provides the opportunity to satisfy customer demands of increased fuel economy, decreased emissions and reducing incremental cost of adoption, while still providing value and performance. One of the major hurdles for adoption of hybrid technologies lies in the current limitations of engine and full vehicle certification. The regulations fail to account for the size and vocational diversity of the medium and heavy duty truck market. This is further complicated by range of truck modifiers that adapt the basic vehicle platform to accommodate the individual customer requirements. As a result, medium and heavy duty truck manufacturers have been prevented from certifying a full vehicle level platform (unlike passenger vehicle manufacturers) due to the current engine only certification requirements. The problem with most hybrid technologies is they affect more than just the engine and after-treatment. In order to bridge the increasing gap between certification and real world fuel economy and emissions, Navistar initiated a study in mid-2010 to look at Hardware-in-the-Loop Simulation (HiLS) with the possibility for Model-in-the-Loop Simulation (MiLS) interfaces as a tool for certification. This effort focused primarily for hybrids, but with the intent applying the same principles to a conventional truck. This study included the evaluation of current certification and regulatory processes, as well as customer in-use data. The goal was to develop a methodology that would minimize the discrepancy between certification, real world fuel economy and emissions, while using existing engine, powertrain or chassis test methodologies where possible. This paper outlines the certification and control considerations required for a pathway to HiLS.