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Development of a MASH TL-3 Compliant Parapet Mounted Fence




Luis Rodriguez, Bob Bielenberg, Cody Stolle, Ronald Faller




When roadways pass over railway tracks, there is a risk that debris from the roadway or pedestrians may fall onto the tracks and interfere with railway operations. Because of this, state Departments of Transportation (DOTs) commonly install debris fences in conjunction with bridge rails over railway tracks. However, the safety performance of debris fence systems when impacted by an errant vehicle has not been demonstrated through full-scale crash testing. Thus, the objective of this research was to develop a new, parapet-mounted debris fence for the Iowa DOT according to safety performance guidelines included in the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH 2016) for Test Level 3 (TL-3). In this study, various state DOT fence designs were reviewed and ranked to select a baseline fence system that would be used as the groundwork for the design of the Iowa DOT fence. Furthermore, crash testing, zone of intrusion studies, and anecdotal real-world crashes were reviewed to understand the expected interaction between an errant vehicle impacting a parapet-mounted fence. The new debris fence was then designed to meet severe weather events inducing high winds and ice accumulation. Impact loading was also considered, primarily in the design of the fence-to-barrier connection. The new debris fence and fence terminations were designed and optimized based on crashworthiness, cost, constructability, and aesthetics. Finally, recommendations were provided to accommodate design modifications, such as adaptations to alternate barriers, changes in geographic location, and considerations for MASH TL-4 impact safety criteria.


Debris Fence, Pedestrian Fence, Railroad, Bridge Rail, Highway Safety, Roadside Appurtenances, MASH 2016

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