From Changning to Qidong, you'd better take S3 17, on the road next to Lianhua Station, or at the intersection of Sannan Road and S3 17, pass through Changning xinhe town and then cross Hezhou Bridge, and you can reach Chenghong Bridge in Qidong County. This route is the best and fastest!
From Changning to Changsha, you can also take S3 17 to Hengkun Expressway, and then transfer to Hengyang to Beijing-Zhuhai Expressway.