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A safety performance evaluation of the Minnesota concrete parapet with brush curb and metal rail (Minnesota Combination Bridge Rail) was conducted for the Minnesota Department of Transportation (Mn/DOT) as part of Year 4 of the Midwest States Regional Pooled Fund Program. The safety performance evaluation of this bridge rail system was conducted and reported according to the criteria specified in Test Level 4 of the National Cooperative Highway Research Program (NCHRP) Report No. 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. This testing involved impacts with an 8000-kg single-unit truck, a 2000-kg pickup truck, and an 820- kg small car. The bridge rail design was modified following the 2000-kg pickup truck test in order to reduce the potential for snagging. After this modification was made, and the system was retested, the safety performance of this system was found to be acceptable and meets the safety standards set forth in Test Level 4 of NCHRP 350.

The Minnesota Department of Transportation's (Mn/DOT's) glue-laminated timber rub rail was developed for situations where a noise barrier will be located within the clear zone and when other types of protection are not considered desirable. The rub rail is intended to prevent an errant vehicle from snagging on the support posts of the noise barrier or on any portions of the noise wall itself. The rub rail is normally not placed as a structural element of the noise barrier. The decision to use a rub rail is sometimes influenced by a desire to keep the traffic-related barrier element farther away from the traffic by affixing it to the noise barrier in lieu of placing a free-standing barrier in front of the noise barrier wall. Therefore, a need existed to evaluate the rub rail design according to the safety performance criteria of the National Cooperative Highway Research Program (NCHRP) Report No. 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. Within the evaluation criteria, all beam and post longitudinal barriers must be capable of developing significant tensile loads and/or flexural loads. Further, adequate anchorage must be provided at the end of the railing system in order for the barrier to perform adequately when struck near the end. Therefore, prior to the evaluation of the system's safety performance, it was necessary to analyze and design the glue-laminated timber rail for use in the noise barrier system.