1. Professor and Chair in Railway Engineering, Dept. of Civil Engineering, Univ. of Pretoria, Pretoria, Gauteng 0002, South Africa (corresponding author).
2. Professor, Dept. of Infrastructure Engineering, Univ. of Southampton, Southampton SO17 1BJ, U.K.; and Extraordinary Professor, Dept. of Civil Engineering, Univ. of Pretoria, Pretoria, Gauteng 0002, South Africa.