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Safety Performance Evaluation of a Modified Perforated Tension Fuse Plate for Dual Support Breakaway Signs




Brian Pfeifer




The Missouri Highway and Transportation Department (MHTD) has been using dual leg breakaway supports for highway signs which include a perforated tension fuse plate developed by the Texas Transportation Institute in 1984. The perforated tension fuse plate is designed to fail in tension, allowing a plastic hinge to form during a vehicular impact. Hinge formation decreases the impact forces applied to a vehicle and reduces the damage to the sign structure. The MHTD found that in some cases the perforated tension fuse plate did not fail when impacted in the field, so the hinge would not activate. The MHTD Engineers redesigned this fuse plate by reducing its thickness so that it would fail upon impact and allow better hinge formation. At the request of the MHTD, two full-scale 1800-lb vehicle crash tests were performed to evaluate the safety performance of the modified fuse plate. The performance of the dual support breakaway sign with a modified tension fuse plate was determined to be acceptable according to criteria set forth in the National Cooperative Highway Research Program Report 230, AASHTO's Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, and Volume 54 of the Federal Register. However, design calculations showed that the fuse plate with reduced cross-sectional area is unable to develop the full capacity of the sign post for carrying windloads. Therefore, an alternate fuse plate design was developed and is presented that should provide both improved impact performance and develop the full wind load capacity of MHTD standard structural supports.


Highway Safety, Roadside Safety, Roadside Appurtenances, Breakaway, Sign Support, Fuse Plate, NCHRP 230, Crash Test, Compliance Test

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