1. Senior Researcher, Korea Institute of Construction Technology, Highway Research Division, 1190, Simindae-Ro, Ilsanseo-Gu, Goyang-Si, Gyeonggi-Do, 411-712, South Korea.
2. Professor, Public Policy Center, 209 SQ, Dept. of Civil and Environmental Engineering, Univ. of Iowa, Iowa City, IA 52242-1527 (corresponding author).