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.
