Applying Social Return on Investment to Risk-Based Transportation Asset Management Plans in Low-Volume Bridges

State departments of transportation implement risk-based transportation asset management systems to standardize risk-oriented procedures and to help decision makers allocate available funds. These procedures can help agencies effectively allocate funding to repair, replace, or maintain their assets in a way that provides the highest overall value to all stakeholders. Because reliable tools with which to measure and compare the socioeconomic impact of distribution of bridge maintenance funds are lacking, decisions are driven by annual average daily traffic (AADT) and the experience of decision makers. Although AADT measures the number of users that would benefit if funding were allocated for a given bridge project, it fails to account for the impact that a given bridge has on the state's or region's economic growth. A reliance on AADT puts low-volume bridges on farm-to-market roads at a disadvantage in competition for scarce funding, as shown by the many structurally deficient low-volume bridges located in croplands of Iowa, a state whose economy is based on agriculture. This paper proposes a method for integrating the socioeconomic impact of funds allocated to maintenance and repair with AADT and for considering the consequences of this decision. The paper demonstrates a stochastic two-way sensitivity analysis social return on investment as the primary metric on two typical Iowa bridges and finds that adding social return on investment to the decision-making process provides a mechanism for more efficiently allocating available resources.