At bioenergy crossroads, should corn ethanol be left in the rearview mirror?

Transportation is responsible for a larger share of greenhouse gas emissions than any other sector of the US economy, making biofuels a promising strategy to mitigate human-driven climate change. The US Renewable Fuel Standard, created by 2007 legislation, mandates that such fuels partially replace petroleum-based ones. So far, however, the mandate has been nearly entirely