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 beta=2.50 for simple span and continuous bridges with spans up to 300-ft in length.

Based on current rating methods, about one in nine of the 607,380 US bridges are considered to be structurally deficient. However, not all these bridges are at risk of collapse as current code-specified analytical methods are generally conservative and may underestimate the true safety levels of existing bridges. For these reasons, there has been considerable interest in developing methods that combine field measured data with analytical models to obtain more accurate assessments of existing bridges. This paper presents a Response-Based Load and Resistance Factor Rating (RB-LRFR) method that utilizes strain data to evaluate the safety of existing bridge members. Appropriate live load factors are calibrated to reflect the uncertainties associated with estimating the parameters and random variables needed to rate a bridge component using field data. The implementation of the proposed methodology is illustrated using a composite steel girder bridge as an example.

The US Federal Bridge Formula was produced as a result of analysis completed over 35 years ago and enacted into US federal law 25 years ago. The bridge formula, "Federal Bridge Formula-B", remains in operation in the US although alternatives to the formula in its current form have periodically been proposed. At this time, there is no limit on commercial vehicles in the form of a bridge formula in the European Union. This paper presents background information on the US Bridge Formula, describes a few alternatives to it that have been proposed in the past and presents observations on its effects if formula would apply to commercial vehicles not only in the EU, but globally.