Substantive changes to the transportation tax bill passed by the Georgia General Assembly might not happen in the 40-day legislative session starting Monday. “We’re not going to have reliable data for what House Bill 170 does until we have at least a year of data in hand,” House Transportation Committee Chairman Christian Coomer, R-Cartersville, told a Gainesville audience Thursday. The bill, which went into effect July 1, eliminated the state fuel sales tax at the gas pump and enacted a 26-cent excise tax.