ABSTRACT
Emergency vehicles such as fire apparatus are often heavier than typical commercial vehicles. The Fixing America’s Surface Transportation Act (FAST Act), signed into law in 2015 includes new truck size and weight provisions that exempt emergency vehicles from meeting the nationwide Interstate truck weight limits on the Interstate System and routes within reasonable access to the Interstate. The emergency vehicles exempted from these weight limits by the FAST Act can create greater load effects in bridges than previously recognized legal loads. NCHRP Project 20-07 Task 410 was initiated in March 2018 by the Transportation Research Board (TRB) with the objective of proposing modifications to the AASHTO Manual for Bridge Evaluation (MBE) to provide guidance for the load rating of bridges for the FAST Act Emergency Vehicles (EVs). In that study, research was undertaken utilizing recent WIM data to establish live load factors and multiple presence factors that are appropriate for emergency vehicles based on likely traffic situations and exposure intervals consistent with those specified in the AASHTO MBE. Load and Resistance Factor Rating (LRFR) EV load factors were then calibrated based on a reliability analysis methodology which is the basis for the current LRFR criteria in AASHTO MBE. The proposed live load factors were calibrated to achieve an average reliability index β=2.50 for simple span and continuous bridges with spans up to 300-ft in length.
