1. School of Traffic and Transportation Engineering, Changsha Univ. of Science and Technology, Changsha, Hunan 410114, China; State Engineering Laboratory of Highway Maintenance Technology, Changsha Univ. of Science and Technology, Changsha, Hunan 410114, China (corresponding author).
2. School of Traffic and Transportation Engineering, Changsha Univ. of Science and Technology, Changsha, Hunan 410114, China.