In August of 2011, the US Environmental Protection Agency issued new Green House Gas (GHG) emissions regulations for heavy duty vehicles. These regulations included new procedures for the evaluation of hybrid powertrains and vehicles. One of the hybrid options allows for the evaluation of an engine plus a hybrid transmission (a powertrain). For this type of testing, EPA has proposed simulating a vehicle following the hybrid vehicle test procedures, including the use of the vehicle cycles and the A to B comparison testing - as required for the full vehicle evaluation option.This paper proposes an alternative approach by defining a powertrain cycle. The powertrain cycle is based on the heavy duty engine emissions cycle - the transient FTP cycle. Simulation and test results are presented showing similar performance over the engine and vehicle cycles. This approach offers several advantages as compared to the procedure described in EPA's GHG rule. Linking the powertrain cycle to the engine cycle ensures an equivalent evaluation as compared to the engine test, and allows evaluation against the engine standard instead of requiring A to B comparison. The use of a normalized powertrain cycle provides for a vehicle independent powertrain evaluation, potentially allowing for a powertrain certification to be applied to many vehicles - as is the case in heavy duty engine emissions certification. Finally, aligning the powertrain test procedure with the engine test program allows manufacturers to build on their existing experience with engine test cycles and test protocols.