If ethanol can only replace 6% of gasoline in the USA, why couldn’t the same reduction be achieved by driving cars that are 6% more efficient?

According to the this publication, which sites the NIST…

If the impacts are aggregated using weights developed by the National Institute of Standards and Technology (NIST), overall, E85 generates approximately 6% to 108% (23% on average) greater impact compared with gasoline, depending on where corn is produced…

 

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