On December 4, 2015, the President signed into law the Fixing America's Surface Transportation Act (FAST Act) (P.L. 114-94), which includes new truck size and weight provisions that effect bridge load rating and posting requirements. Among those provisions is the exemption of emergency vehicles from meeting the nationwide Interstate truck weight limits set forth in 23 U.S.C. 127(a). The emergency vehicles exempted from these weight limits by the FAST Act can create greater load effects in certain bridges than the previous legal loads. Research needs to be undertaken to establish whether existing load factors, multiple presence factors based on likely traffic situations, and exposure intervals as specified in the AASHTO Manual for Bridge Evaluation are appropriate for the emergency vehicles; further these load factors may need to be developed or calibrated to the reliability analysis in the AASHTO Manual for Bridge Evaluation.

 

The objective of this research is to propose modifications to the load factors for the emergency vehicles in the AASHTO Manual for Bridge Evaluation (load factor rating “LFR” and load and resistance factor rating “LRFR”). For the LRFR, the load factors shall be calibrated to the reliability analysis in the AASHTO Manual for Bridge Evaluation with appropriate modifications.