PREFACEAASHTO first published Guide Specifications for Horizontally Curved Highway Bridges in 1980. These guide specifications included Allowable Stress Design (ASD) provisions developed by the Consortium of University Research Teams (CURT) and approved by ballot of the AASHTO Highway Subcommittee on Bridges and Structures in November 1976. CURT consisted of Carnegie-Mellon University@ the University of Pennsylvania@ the University of Rhode Island and Syracuse University. The 1980 guide specifications also included Load Factor Design (LFD) provisions developed in American Iron and Steel Institute (AISI) Project 190 and approved by ballot of the AASHTO Highway Subcommittee on Bridges and Structures in October 1979. The guide specifications covered both I-girders and box girders.Changes to the 1980 guide specifications were included in the AASHTO Interim Specifications??Bridges for the years 1981@ 1982@ 1984@ 1985@ 1986@ and 1990. A new version of the Guide Specifications for Horizontally Curved Highway Bridges was published in 1993. It included these interim changes@ and additional changes@ but did not reflect the extensive research on curved-girder bridges that has been conducted since 1980@ or many important changes in related provisions of the straight-girder specifications.The present specifications and commentary were developed to correct these deficiencies. They reflect the current state-of-the-art and are consistent with present straight-girder specifications@ except as noted. They were developed in National Cooperative Highway Research Program (NCHRP) Project 12-38 and are fully documented in NCHRP Report 424: Improved Design Specifications for Horizontally Curved Steel Girder Highway Bridges.The following terms are used to identify particular specifications:? Bridge Welding Code refers to the 1996 edition of ANSI/AASHTO/AWS Bridge Welding Code and In-terim Specifications@??"previous curved-girder specifications?? or Guide Spec refers to the 1993 AASHTO Guide Specifications for Horizontally Curved Highway Bridges.??AASHTO or AASHTO LFD/ASD refers to the 1996 AASHTO Standard specifications for Highway Bridges@ 16th Edition and Interim Specifications@??AASHTO LRFD refers to the 1998 AASHTO LRFD Bridge Design Specifications@ Second Edition and Interim Specifications.Curved girder specifications based on the present AASHTO LFD specifications will be incorporated into the AASHTO Load and Resistance Factor Design (LRFD) specifications under NCHRP Project 12-52. An extensive theoretical and experimental research program is also being conducted on curved-girder bridges under sponsorship of the Federal Highway Administration (FHWA). This program should permit further future improvements in the present curved girder specifications.