| Conditions and Performance
Chapter Listing
Conditions and
Performance Home Page
Introduction
Summary
Economics-Based Approach to Transportation
Investments
Highway
Investment Requirements
Bridge
Investment Requirements
Combined
Highway and Bridge Investment Requirements
Transit
Investment Requirements
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The investment requirements scenarios in this report project total
investment requirements for the period 1998-2017. The Eliminate Deficiencies
scenario is the equivalent of the Cost to Improve Bridge Conditions
shown in previous reports. The Maintain Backlog scenario is the
equivalent of the Cost to Maintain Bridge Conditions shown in previous
reports. The scenarios were renamed to clarify their intent, and to emphasize
that the bridge investment requirements analyses focus on bridge deficiencies,
rather than average bridge conditions.
| Q HERS is used as an
economic tool for roadway investment analysis. Is there a similar tool for
bridge analysis? |
| A The national Bridge
Investment Analysis System (BIAS) is currently being developed to add an
economic component to the bridge analysis. BIAS is based on the optimization
procedures of Pontis, a bridge management system developed initially with input
from FHWA, several States, the Transportation Research Board, and other
interests. Pontis is now supported by the American Association of State Highway
and Transportation Officials and is being further enhanced at the suggestion of
the States for use as their bridge management system. Pontis was developed
to analyze individual bridges, using data on the condition of a variety of
bridge elements. BIAS takes a similar approach to bridge analysis, but relies
on the National Bridge Inventory which is less detailed. BIAS can not analyze
individual bridges, but can provide information on a more aggregate, national
level basis, without requiring all the detailed information that Pontis needs.
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Eliminate Deficiencies
Scenario
This scenario would eliminate the existing bridge investment backlog, and
correct other deficiencies that are expected to develop over the next
20 years. The average annual investment required under this scenario is
$10.6 billion. Exhibit 7-7 shows the 20-year total and average investment
requirements for each functional class under this scenario. This table also
contains the number of bridges that would be rehabilitated or replaced during
the analysis period.
Exhibit 7-7. Bridge
Investment Requirements 1998-2017 Eliminate Deficiencies Scenario
Maintain Backlog
Scenario
Under the Maintain Backlog scenario, the bridge investment backlog
would be maintained at its current level. Under this scenario, existing
deficiencies and newly accruing deficiencies would be selectively corrected, to
minimize the investment required to maintain the same backlog of deficient
bridges in 2018 that exists in 1998. The average annual investment required
under this scenario is estimated at $5.8 billion. Exhibit 7-8 shows the
20-year total and average investment requirements under this scenario, by
functional class, as well as the number of bridges that would be rehabilitated
or replaced during the analysis period.
Exhibit 7-8. Bridge Investment
Requirements 1998-2017 Maintain Backlog Scenario
It should be noted that the Maintain Backlog scenario focuses on
deficient bridges, rather than on average bridge conditions. Average bridge
conditions would not necessarily be maintained under this scenario.
| Q Are any preliminary
results available from the BIAS model? |
| A The National Bridge
Investment Analysis System (BIAS) is an analytical system being developed as a
bridge investment/performance tool to supplement the Bridge Needs and
Investment Process (BNIP) that has been used for a decade to estimate bridge
capital investment requirements. BIAS adds economic analysis to this estimation
process. This box contains provisional results of BIAS so the reader may become
aware of the model and its possible future use to project bridge investment
requirements. Please note that future results may differ from the interim
results presented here. BIAS estimates that an annual bridge investment from
all levels of government of $6.4 billion for the 20-year period 1999 to 2018
would maintain the same overall backlog amount in 2018 as in 1999. However,
this figure cannot be directly compared to BNIP results because the BIAS figure
includes some amount of maintenance or minor rehabilitation not included in
BNIP. It is estimated that the average benefit cost ratio for the predicted
improvements over the 20-year period would be about 4.0, meaning that an
average of $4 dollars of benefits would be obtained from every dollar invested.
Much of these benefits would derive from trucks not having to detour over a
longer route because of deficient bridge load carrying capacity.
An annual investment of $10.7 billion for the same 20-year period is
projected to eliminate the backlog for major improvements such as replacement
and functional improvements. It would not eliminate the requirement for
continued rehabilitation and maintenance. The average benefit cost ratio for
this scenario is estimated to be about 2.7. Again, this should be taken as a
provisional result.
These BIAS results are tentative and should not be taken as directly
comparable to the BNIP results contained elsewhere in this report. Future
enhancements to BIAS may incorporate further refinements to relationships
contained in the model and information not currently included, such as the
benefits to the user of various types of bridge improvements. Such further
enhancements may modify the results.
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