Methodology for ranking relative importance of structures to Virginia's roadway network.
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2016-06-01
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Abstract: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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