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Design and Testing of a Breakaway Base for a Cluster Box Unit and a Neighborhood Delivery & Collection Unit




Gene Paulsen, Ronald Faller, John Reid




The United States Postal Service (USPS), in response to the potential threat to motor vehicle and occupant safety should a collision occur with roadside-installed centralized-delivery equipment such as Neighborhood Delivery & Collection Box Units (NDCBUs) and Cluster Box Units (CBUs), requested that the Midwest Roadside Safety Facility (MwRSF) design a new breakaway mechanism to potentially improve the safety performance of these units. A literature search and evaluation was performed to investigate the current state-of-the-art in breakaway mechanisms. Design calculations and bogie impact tests were conducted on several conceptual designs in order to select the best alternative. The final design was tested with a 2.2-kN (500-lb) horizontal static pull test, and a 500 hour salt spray test to determine the durability of the breakaway design. Additionally, LS-DYNA3D, a large deformation nonlinear finite element analysis (FEA) code, was used to simulate actual crash test scenarios on the CBU's and estimate its relative safety performance. The results of the study produced a new breakaway base that potentially improves the safety performance of the CBU when impacted by a vehicle. FEA predicted that the CBU's would meet the safety performance criteria set forth in NCHRP 350 with the exception of the occupant compartment intrusion criteria. FEA methods are currently unable to determine the extent, if any, of occupant compartment intrusion into the windshield, due to the CBU projectile. It is recommended that full-scale crash tests be performed in order to investigate windshield intrusion, as well as to further evaluate the safety performance of the system. This testing would be required to fully satisfy NCHRP 350 recommendations.


Roadside safety, mailbox support, breakaway support, finite element analysis, computer simulation

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