A new traffic light was just approved to handle growing congestion at the intersection of Cliff Drive and Las Positas Road, but the state funding for the new signal won’t be available for at least two more years. In the meantime, city traffic engineers will continue to explore the costs — and funding options — for building a roundabout there instead. By all reckoning, a roundabout can handle the traffic load more efficiently than a traffic signal and cause far fewer greenhouse gases. But initial estimates suggest the roundabout will cost $1.1 million more than the $900,000 signal. Councilmember Grant House said other communities have managed to build comparably sized roundabouts for far less. Caltrans has committed to provide $750,000 of the money needed to install the new traffic signal. No money has been identified to date for a roundabout.