On Thursday, the California Air Resources Board will vote on whether to require fewer zero-emissions vehicles on the state’s roads in coming years. As it stands now, automakers must sell 25,000 zero-emission vehicles by 2014 and an additional 50,000 by 2017. Under the proposed changes, the numbers would drop to 2,500 by 2014 and 25,000 by 2017, with the difference made up by selling plug-in hybrids or vehicles with hydrogen-powered internal combustion engines. Proponents of the change, including some automakers, say that it’s a more realistic requirement since it focuses on closer-to-market technologies. However, the Union of Concerned Scientists and others say that while more plug-in hybrids would be welcome in the state, California’s current requirement for ZEVs is an important driver of technology. “California should open the door wide for plug-in hybrids,” said UCS’ Spencer Quong. “But if the ZEV program is going to get the job done, it still needs to pave the way for millions of battery electric and fuel cell vehicles on the road.”