Methodology for Ranking Relative Importance of Structures to Virginia’s Roadway Network

About the report:

In 2011, the Structure and Bridge Division of the Virginia Department of Transportation (VDOT) requested assistance from the Virginia Transportation Research Council to develop a structure scoring tool that would rank the relative importance of VDOT-maintained structures to the highway network and to the economy of Virginia. Although tools existed to rank structures by condition and age, no scoring tool existed that systematically incorporated non–condition-based structure features known to be relevant to decision-makers, such as intensity of travel demand for a structure relative to its capacity, the relative magnitude of user costs imposed by potential closure of the structure, and the relative impact of closure of a particular structure on key nearby facilities.

The new tool produces a structure score dubbed the “Importance Factor” score (IF score) for all open structures in VDOT’s current inventory database. IF scores are based on current data in the structure inventory database on which other structure scoring tools in current use are based, supplemented by geopositional data that identify schools, hospitals, and fire/rescue stations within half-mile increments of each eligible structure up to 3 miles. Beyond 3 miles, a structure is assumed to provide negligible mobilization options to these “key” facilities. IF scores are relative rankings; thus they have no inherent meaning at face value.

The tool was statistically tested and adjusted to ensure that the structure characteristics selected to generate IF scores would have known and measurable impacts in accordance with the intentions of an expert panel composed of staff from VDOT’s Structure and Bridge Division. Consequently, the relative influences of the factors that determine IF scores are assured by model specification.

IF scores are relative rankings of eligible VDOT-maintained structures and may be updated each time a structure inventory database is refreshed. To existing structure scoring tools that measure relative funding need among structures based on condition and age factors, the IF score adds the critically important dimension of the structure’s role in the highway system and the economy of Virginia.

The study recommends that VDOT’s Structure and Bridge Division include consideration of IF scores in making closure decisions and in the process of allocating funds; that VDOT’s Structure and Bridge Division consider the new IF rankings, alongside condition and budget data, in decisions relating to bridge maintenance such as ranking structures for rehabilitation or replacement, restorative maintenance, and preventative maintenance actions when preparing the annual needs assessment; and that VDOT’s Traffic Engineering Division and Information Technology Division provide support to VDOT’s Structure and Bridge Division to automate the export of relevant data that are incorporated into the IF tool from data sources outside the Structure and Bridge Division.

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