State highway agencies across the country are upgrading standards, policies, and processes to satisfy the 2016 AASHTO/FHWA Joint Implementation Agreement for MASH. Existing vehicle collision loads used for reviewing bridge deck overhangs are specified in Section 13 of the AASHTO LRFD [Load and Resistance Factor Design] Bridge Design Specifications, 9th edition (LRFD BDS), and are based on crash testing criteria according to the Contractor’s final report for NCHRP Project 20-07(395), NCHRP Report 350. To meet the MASH implementation agreement, the loading requirements and analysis method for the bridge deck overhang should be investigated and the AASHTO LRFD BDS modified accordingly. Research was urgently needed to ensure public safety, satisfy the AASHTO MASH and LRFD bridge design requirements, and facilitate optimal use of agency funds.

Under NCHRP Project 12-119, “MASH Railing Load Requirements for Bridge Deck Overhang,” the University of Nebraska–Lincoln was asked to (1) propose modifications to the AASHTO LRFD BDS related to loading requirements consistent with the AASHTO MASH impact conditions for bridge deck overhangs and (2) develop examples to demonstrate the application of the proposed modifications. The research included a literature review and analysis and design of bridge deck overhang for concrete barriers, open concrete railings, steel posts-on-decks, and steel posts-on-curbs subjected to a range of MASH Test Levels. The research team recommended important draft language for consideration by AASHTO in the next update of the LRFD BDS.

In addition to this final report, Appendices B through E, containing four design examples, are available on the National Academies Press website (nap.nationalacademies.org) by searching for NCHRP Research Report 1078.