Minnesota Mailbox (405160-6)

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TTI Research Supervisor: Roger P. Bligh, Ph.D., P.E. Texas Transportation Institute Texas A&M University System TAMU 3135 College Station, Texas 77843-3135 (979) 845-4377 [email protected] Pooled Fund Technical Representative: Michael Elle, P.E. Design Standards Engineer Minnesota Department of Transportation 395 John Ireland Blvd, MS 696 St. Paul, MN 55155-1899 (651) 366-4622 [email protected]


The MinnDOT swing-away mailbox support was tested and evaluated by the Texas A&M Transportation Institute (TTI) in 1993 in accordance with the guidelines outlined in NCHRP Report 350. The performance of a single mailbox support was found to be marginally acceptable. Although the windshield of the impacting vehicle was shattered, high-speed film indicated that the mailbox assembly did not intrude or penetrate into the occupant compartment. Subsequent to the crash testing, design modifications were made to the swing-away mailbox support by MINNCOR Industries. The objective of this project is to evaluate the MinnDOT swing-away mailbox support as modified by MINNCOR Industries and determine if it complies with recommended criteria for breakaway supports contained in NCHRP Report 350. In the previous testing performed on the original swing-away mailbox design, substantial windshield damage was observed. Since NCHRP Report 350 does not provide objective criteria for assessing windshield damage, the Federal Highway Administration stated that the results of the crash tests on the modified design will be considered acceptable if the windshield damage and potential for occupant compartment intrusion is no worse than that caused by the original MinnDOT design. The evaluation consisted of two high-speed crash tests in which the mailbox support system was impacted at two different locations. The impact conditions followed those of NCHRP Report 350 Test Designation 3-61, which consists of an 820 kg (1800-lb) vehicle impacting head-on (i.e., zero degrees) at a speed of 100 km/h (62 mph). The modified MinnDOT swing-away mailbox assembly was found to meet the requirements of NCHRP Report 350 as a Test Level 3 (TL-3) breakaway support structure.