As regulatory agencies in the U.S. work on the second phase of heavy-duty vehicle greenhouse gas (GHG) and efficiency standards, one of the key decisions they face concerns the regulatory certification pathways. The question of whether to maintain separate standards for the engine and the full vehicle, as in the first phase of the regulation, is hotly debated. In addition, the agencies must decide what upgrades to the testing and certification procedures can be made based on lessons learned from Phase 1. This analysis develops six possible options for certification, using Phase 1 and publicly expressed industry viewpoints as a guide. The authors then evaluate these options based on seven criteria developed to compare the certification procedures’ relative merits.