Source: U.S. EPA 1999
5.2 Effect of Vehicle Stock Mix
Alternative vehicle fuel economy was estimated from a baseline gasoline vehicle fuel economy for a subcompact car class.
Alternatively, one could estimate the fuel economy of the class or size of the replaced vehicle as the baseline. This approach is more suitable for comparing alternative fueled vehicles to gasoline vehicles rather than evaluating vehicle that would be likely PZEV candidates.
Fuel economy ratios were estimated for each technology/fuel. These ratios are indications of how much more each technology would expect to achieve in terms of fuel economy (on an energy basis) compared to the baseline conventional vehicle. Since it is not possible to obtain fuel economy data for a consistent set of vehicles with similar attributes, fuel economy is estimated from energy efficiency data and the fuel’s heating value. The Energy Economy Ratio (EER) is the ratio of alternative vehicle energy economy to the baseline gasoline vehicle energy economy (on a lower heating value basis). These values were based upon data shown above.