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Hybrid vehicles may respond to fuel variables in unique ways; they could even require a unique driveability test. The Coordinating Research Council (CRC) conducted a program to determine the effect of ethanol content on driveability performance under cool ambient conditions. In addition to the 27 vehicles in the main fleet, four hybrid electric vehicles (HEVs) were tested using the same fuels and driveability procedure. These HEVs responded to fuel in a manner similar to conventional vehicles; however, the HEVs showed unique driving characteristics not well captured in the existing test.

From 1995 to 1997, the Coordinating Research Council (CRC) conducted a cold-start driveability program to evaluate the behavior of lower volatility fuels at cold, intermediate, and warm ambient temperatures. The program used 135 vehicles to evaluate 87 hydrocarbon, MTBE blended, and ethanol blended fuels. Evaporative driveability index equations (EDIs) were developed using the test design fuel variables (E158°F, E200°F, E300°F), and three other variable sets: (E158°F, E250°F, E330°F), (T10, T50, T90), and (E70°C, E100°C, E140°C). The models that best fit the data contained oxygenate offsets. Overall, the best indices are the E70°C, E100°C, E140°C equation and the DI equation with offsets.