Infrastructure Asset Management Bridge Value and Performance

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Infrastructure Asset ManagementBridge Value and
Performance

• April 25, 2001
• Terry Leatherwood, P.E.

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Tasks Given to the Bridge Office

• Determine the Replacement Value of the existing
  Bridge Inventory owned and maintained by the
  State of Tennessee.
• Create an Objective Standard (Rating Scale) that
  may be used to verify that the State is
  maintaining the Quality of the Bridge Inventory.

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Task 1 - Replacement Value

• Tennessee has a method of computing Bridge
  Replacement Value based upon National Bridge
  Inventory Data.
• First, the estimated replacement length of the
  bridge is computed using the Expansion Factor
  Formulas given in the FHWA Recording and Coding
  Guide (Page 61).

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Replacement Value (Continued)

• The estimated Replacement Width is based upon
  Average Daily Traffic and the Deck Geometry Table
  in the Recording and Coding Guide (Pages 49-50).
• Compute a Base Cost in Dollars per unit of Deck
  Area. The formula uses the maximum Span Length of
  the existing bridge as input.
• Adjust the Base Cost using Inflation and
  Percentage Increase Factors.

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Replacement Value (Continued)

• Multiply the Adjusted Base Cost by the estimated
  Deck Area of the New Bridge.
• Sum up the calculations for all Tennessee Bridges
  subdivided by Age.
• Present the data in Tabular and Chart Form.

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Replacement Value Results
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Replacement Value Results
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Replacement Value Summary

• The Method is Based directly upon National Bridge
  Inventory (NBI) data available Nationwide.
• TDOT has Historical Data detailing Total
  Transportation Expenditures.
• TDOT apportions these Expenditures based upon the
  Replacement Costs estimates made for Roadways and
  Bridges.

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Task 2 - Rating Scale

• The Bridge Office considered various methods to
  develop a Rating Scale.
• The Options included basing it upon the
  Sufficiency Rating, Pontis Bridge Management Data
  or upon the percentage of Deficient and Obsolete
  Deck Area.
• The selected system was to use Deficient and
  Obsolete Deck Area.

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Structural Deficiency

• For bridges, Structural Deficiency has a specific
  meaning.
• It is based upon NBI Items 58, 59, 60, 62, 67 and
  71.
• These correspond to Deck, Superstructure,
  Substructure, Culvert conditions plus Structural
  Evaluation and Waterway Adequacy respectively.

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Functional Obsolescence

• This also has a specific meaning for Bridges.
• It is based upon NBI Items 68, 69, 72, 67 and 71.
• These correspond to Deck Geometry,
  Underclearances, Approach Roadway Alignment,
  Structural Evaluation and Waterway Adequacy
  respectively.

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Structurally Deficient and Functionally Obsolete
Areas

• The FHWA Goal for this category is that the Sum
  of these Areas should be less than 25 of Total
  area. To turn this around, 75 or more of Total
  Deck Area should not be either Deficient or
  Obsolete.
• The Current Non-Deficient Percentage for all TDOT
  Owned Bridges stands at 78.65 (i.e. 21.35 is
  Deficient or Obsolete).

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Selected Method

• The Bridge Inspection Offices believes that
  basing a rating upon percentage of deficient and
  obsolete deck area is the best method.
• Tennessee will follow the FHWA Guideline and set
  our standard at keeping our Non-Deficient
  Percentage above 75.
• Therefore, the goal would be to maintain a score
  of 75 or better on a 100 point scale.

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Questions?