1. School of Qilu Transportation, Shandong University, 12550 E. Second Ring Rd., Jinan, Shandong 250002, P. R. China
2. Shandong Hi-speed Group Co., Ltd., Shandong Expressway Building, 8 Longao N. Rd., Lixia District, Jinan, Shandong 250014, P. R. China
3. School of Qilu Transportation, Shandong University, 12550 E. Second Ring Rd., Jinan, Shandong 250002, P. R. China (Corresponding author), e-mail: ming.liang@sdu.edu.cn, https://orcid.org/0000-0002-5217-8404
4. School of Qilu Transportation, Shandong University, 12550 E. Second Ring Rd., Jinan, Shandong 250002, P. R. China (Corresponding author), e-mail: zhanyong-y@sdu.edu.cn, https://orcid.org/0000-0002-9980-5444