Diesel electric hybrid powertrains and methods of operating and testing such powertrains are disclosed. Certain exemplary embodiments comprise test and certification methods in which a controller operates a diesel engine alone, an integrated motor/generator alone, or both the diesel engine and the motor/generator to provide brake torque at a common output shaft according to predetermined duty cycle criteria. Emissions are measured based upon criteria accounting for the effects of regenerative braking, engine shut off, and other operational modes unique to hybrid powertrains. Further exemplary embodiments comprise hybrid powertrain systems and methods of operating the same meeting performance and emissions requirements including respective limits on NOx, hydrocarbon, particulate matter, CO, and CO2 without reliance conventional emissions reduction devices or techniques.