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1 INTRODUCTION There has been interest for several decades in developing selection guidelines for the multiple performance, service or test levels for bridge railings in the roadside safety community. Since bridges cross over large spans of space they often cross significant features such as busy transportation corridors. In addition, bridges carry heavy vehicles sometimes with dangerous cargos, such as fuel and hazardous chemicals. The consequences to public safety of a heavy truck penetrating through or rolling over a bridge railing or a passenger vehicle vaulting a bridge railing present additional risks not considered for crashes with other types of roadside barriers. Numerous bridge railings have been designed and crash tested in the past several decades according to one of the several multiple test level approaches so there are a wide variety of different test level bridge railings available. What has never been established, however, are the criteria for selecting when a higher test level railing is needed based on the specific traffic and site characteristics of individual bridges. The American Association of State Highway and Transportation Officials (AASHTO) Roadside Design Guide (RDG) and LRFD Bridge Design Specification recognize the multiple test level approach but give only very general guidance about why a higher test level bridge railing might be used. [AASHTO06] At present, highway agencies must make decisions on which test level is appropriate for each site on an ad hoc basis. The objective of this project was to develop proposed selection guidelines to assist bridge engineers and highway designers in selecting an appropriate test level for bridge railings based on specific site and traffic conditions. The focus of the study was on TL2 through TL5 railing. TL1 bridge railings involve very low volume and low speed applications which are not widely encountered and are generally not considered practical except in some special situations like park roads. At the other end of the spectrum, TL6 bridge railings are presumably intended for locations where the severity of a penetration or rollover would be exceptionally catastrophic. A TL6 bridge railing would be warranted to maintain public support for the highway project, even if the barrier is not necessarily cost effective. In addition, there is only one crash tested TL6 bridge railing available at this time. It requires specially designed deck details to support the impact loads and additional dead load of the barrier. The vast majority of bridge railings that will be practical for use are, therefore in the TL2 through TL5 range. The basic approach used in this project was a risk-based approach where the frequency and severity of crashes with bridge railings are estimated and the risk of observing a serious or fatal injury crash calculated. The third version of the Roadside Safety Analysis Program (RSAP) was developed to perform cost-benefit analysis, but was expanded during this research effort to preform risk-analyses as well. This report documents the research conducted to populate the RSAP database, run the RSAP simulations, and the resulting selection guidelines for the selection of MASH TL2 through TL5 bridge railings. The literature reviewed and a survey of practitioners are presented in the first several chapters, the data gathered and the analysis conducted is presented alongside a discussion of the decisions made throughout the research in subsequent chapters. Finally, the proposed selection process and selection tables to accompany
2 the process are presented at the end of the document with accompanying discussion and alternative selection tables for use in the establishment of policy. The recommendations are presented in their entirety in Appendix B for a quick reference.
