Hall County recently introduced 20 alternatively powered buses to its fleet and is already looking to add more.Over the summer, Hall County Schools purchased 20 buses that run on liquefied petroleum gas, or propane, as it’s more commonly known. The buses, officials and drivers said, have met expectations and the system has signed on to add 10 more, including six special education buses. “We’re still very pleased with them,” said Jewel Armour, Hall County Schools executive director of operations.