This, it said, using the EPA's own greenhouse gas (GHG) equivalencies calculator, was the equivalent of removing 951,600 passenger vehicles from the road this year. CO2e includes carbon dioxide, nitrous oxide and methane.

The University of Illinois at Chicago said the RFS "results in substantial GHG savings by stimulating innovation at the feedstock production and biorefinery level. However, the current RVO (renewable volume obligations) fails to fully realize these GHG savings."

The University of Illinois at Chicago's research engineer, Iris Caldwell, and principal research economist, Stephen Mueller, presented their analysis during the EPA's public hearing for its 2014, 2015 and 2016 targets in Kansas in June.

"Our work has shown that the biofuels industry has a uniquely high rate of innovation and technology adoption, which has resulted in steady reductions in GHG impacts. Specifically, our research shows energy use (and related GHG emissions) by biorefineries has been trending downward over the past decade," they said.

They added recent analyses show potential indirect land-use change emissions are lower than the EPA's initial estimates due to :

1. An evolving understanding of the elasticity of land transitions and yield-price relationships

2. Better addressing of ethanol co-product substitutions in animal feed markets

3. Better understanding and data availability of global land types

4. Carbon adjustments during land transitions

Caldwell and Mueller's full testimony can be read here.