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Status of the Nation's Highways, Bridges, and Transit:
2002 Conditions and Performance Report

Chapter 7: Capital Investment Requirements
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Index
Introduction
Highlights
Executive Summary
Part I: Description of Current System
Ch1: The Role of Highways and Transit
Ch2: System and Use Characteristics
Ch3: System Conditions
Ch4: Operational Performance
Ch5: Safety Performance
Ch6: Finance

Part II: Investment Performance Analyses
Ch7: Capital Investment Requirements
Ch8: Comparison of Spending and Investment Requirements
Ch9: Impacts of Investment
Ch10: Sensitivity Analysis

Part III: Bridges
Ch11: Federal Bridge Program Status of the Nation's Bridges

Part IV: Special Topics
Ch12: National Security
Ch13: Highway Transportation in Society
Ch14: The Importance of Public Transportation
Ch15: Macroeconomic Benefits of Highway Investment
Ch16: Pricing
Ch17: Transportation Asset Management
Ch18: Travel Model Improvement Program
Ch19: Air Quality
Ch20: Federal Safety Initiatives
Ch21: Operations Strategies
Ch22: Freight

Part V: Supplemental Analyses of System Components
Ch23: Interstate System
Ch24: National Highway System
Ch25: NHS Freight Connectors
Ch26: Highway-Rail Grade Crossings
Ch27: Transit Systems on Federal Lands

Appendices
Appendix A: Changes in Highway Investment Requirements Methodology
Appendix B: Bridge Investment/Performance Methodology
Appendix C: Transit Investment Condition and Investment Requirements Methodology
List of Contacts

Highway and Bridge Investment Requirements

This section presents the projected investment requirements for highways and bridges for two primary performance targets. The Cost to Maintain Highways and Bridges represents the annual investment necessary to maintain the current level of highway system performance. The Cost to Improve Highways and Bridges identifies the level of investment that would be required to significantly improve system performance in an economically justifiable manner. The impacts of a wider range of alternative investment levels on various measures of system performance are shown in Chapter 9. Chapter 9 also explores recent trends in highway expenditures compared to recent changes in system performance.

The combined highway and bridge investment requirements are drawn from the separately estimated scenarios for highways and for bridges, and from external adjustments to the two models. These scenarios are defined differently, due to the different natures of the models used to develop them. However, it is useful to combine them in order to show combined investment. This is particularly helpful when trying to compare these scenarios to current or projected investment levels, since amounts commonly referred to as “total highway spending” or “total highway capital outlay,” include expenditures for both highways and bridges. Chapter 8 compares current highway and bridge spending with the investment requirements outlined in this section.

The average annual investment required to Improve Highways and Bridges over the 20-year period 2001-2020 is projected to be $106.9 billion in 2000 dollars. The average annual Cost to Maintain Highways and Bridges is projected to be $75.9 billion (also in 2000 dollars).

Cost to Improve Highways and Bridges

The average annual Cost to Improve Highways and Bridges is broken down by functional class and type of improvement in Exhibit 7-2. The estimated investment requirements for urban arterials and collectors total $61.3 billion, or 57.3 percent of the total average annual Cost to Improve Highways and Bridges. Investment requirements on rural arterials and collectors are $23.8 billion or 22.3 percent of the total, while the investment requirements for rural and urban local roads and streets total $21.8 billion (20.4 percent).

The Cost to Improve Highways and Bridges scenario combines the Maximum Economic Investment scenario from the Highway Economic Requirements System (HERS) and the Eliminate Deficiencies scenario from National Bridge Investment Analysis System (NBIAS) with external adjustments to the two models.

Cost to Maintain Highways and Bridges

Exhibit 7-3 shows the average annual Cost to Maintain Highways and Bridges by type of improvement and functional class. The estimated investment requirements for urban arterials and collectors under this scenario total $43.2 billion, or 56.9 percent of the average annual Cost to Maintain Highways and Bridges. Investment requirements for rural arterials and collectors total $17.3 billion (22.7 percent), while the investment requirements for rural and urban local roads and streets total $15.5 billion (20.4 percent).

The Cost to Maintain Highways and Bridges scenario combines the Maintain User Costs scenario from HERS and the Maintain Backlog scenario from NBIAS with external adjustments to the two models.

    
Exhibit 7-2

Average Annual Investment Required to Improve Highways and Bridges (Billions of 2000 Dollars)
 
FUNCTIONAL CLASS SYSTEM PRESERVATION SYSTEM EXPANSION SYSTEM ENHANCEMENTS TOTAL
HIGHWAY BRIDGE TOTAL
Rural Arterials & Collectors
Interstate
$3.0
$0.6
$3.6
$1.9
$0.4
$5.8
Other Principal Arterial
$3.2
$0.6
$3.8
$1.5
$0.6
$5.9
Minor Arterial
$2.8
$0.6
$3.4
$0.9
$0.5
$4.7
Major Collector
$3.3
$1.2
$4.6
$0.3
$0.4
$5.3
Minor Collector
$1.0
$0.6
$1.5
$0.4
$0.2
$2.1
Subtotal
$13.3
$3.5
$16.8
$4.9
$2.1
$23.8
Urban Arterials & Collectors
Interstate
$5.5
$1.3
$6.8
$13.2
$1.2
$21.1
Other Freeway & Expressway
$2.2
$0.5
$2.7
$5.7
$0.5
$8.9
Other Principal Arterial
$4.0
$0.6
$4.6
$8.8
$1.5
$14.9
Minor Arterial
$3.2
$0.4
$3.6
$6.3
$1.0
$11.0
Collector
$2.2
$0.2
$2.4
$2.4
$0.5
$5.3
Subtotal
$17.2
$3.0
$20.2
$36.4
$4.6
$61.3
Subtotal Rural and Urban
Rural and Urban Local
$8.6
$2.8
$11.5
$8.6
$1.7
$21.8
Total
$39.1
$9.4
$48.5
$49.9
$8.4
$106.9
Source: Highway Economic Requirements System and National Bridge Investment Analysis System.

Investment Requirements by Improvement Type

Exhibits 7-2 and 7-3 also show investment requirements by type of improvement. The investment requirements are classified into three categories: system preservation, system expansion, and system enhancement, which are defined in Chapter 6. System preservation, as defined in this report, consists of the capital investment required to preserve the condition of the pavement and bridge infrastructure. This includes the costs of resurfacing, rehabilitation, and reconstruction, but does not include routine maintenance costs. System expansion includes the costs related to increasing system capacity by widening existing facilities or adding new roads and bridges. System enhancements include safety enhancements, traffic operations improvements, and environmental improvements. Appendix A describes how the investment requirements modeled by HERS and NBIAS were allocated among the three types of improvements.

Exhibit 7-4 displays investment requirements by improvement type for rural and urban areas, for each scenario.

System Preservation

Average annual system preservation investment requirements are estimated to be $48.5 billion under the Cost to Improve scenario and $37.1 billion under the Cost to Maintain scenario. These totals comprise constitute 45.4 and 48.8 percent, respectively, of the totals for the two scenarios. Figures 7-2 and 7-3 also indicate that bridge preservation investments represent about one-fifth of total preservation investment requirements under each scenario. As shown in Exhibit 7-4, system preservation makes up a much larger share of total investment requirements in rural areas than in urban areas.

    
Exhibit 7-3

Average Annual Investment Required to Maintain Highways and Bridges (Billions of 2000 Dollars)
 
FUNCTIONAL CLASS SYSTEM PRESERVATION SYSTEM EXPANSION SYSTEM ENHANCEMENTS TOTAL
HIGHWAY BRIDGE TOTAL
Rural Arterials & Collectors
Interstate
$2.1
$0.5
$2.6
$1.6
$0.3
$4.5
Other Principal Arterial
$2.5
$0.5
$3.0
$0.9
$0.4
$4.3
Minor Arterial
$2.2
$0.5
$2.7
$0.3
$0.3
$3.3
Major Collector
$2.1
$1.0
$3.1
$0.2
$0.3
$3.6
Minor Collector
$0.7
$0.4
$1.1
$0.3
$0.2
$1.5
Subtotal
$9.6
$2.9
$12.5
$3.3
$1.5
$17.3
Urban Arterials & Collectors
Interstate
$5.2
$1.0
$6.2
$11.3
$0.8
$18.4
Other Freeway & Expressway
$1.9
$0.4
$2.3
$4.2
$0.3
$6.8
Other Principal Arterial
$3.1
$0.5
$3.6
$4.0
$1.0
$8.7
Minor Arterial
$2.3
$0.4
$2.6
$2.8
$0.7
$6.1
Collector
$1.6
$0.2
$1.7
$1.1
$0.4
$3.2
Subtotal
$14.0
$2.4
$16.4
$23.5
$3.3
$43.2
Subtotal Rural and Urban
Rural and Urban Local
$6.1
$2.0
$8.1
$6.1
$1.2
$15.5
Total
$29.7
$7.3
$37.1
$32.9
$6.0
$75.9
Source: Highway Economic Requirements System and National Bridge Investment Analysis System.

System Expansion

The $49.9 billion in average annual investment requirements for system expansion represent 46.7 percent of the total Cost to Improve Highways and Bridges. Comparable figures for the Cost to Maintain scenario are $32.9 billion and 43.3 percent. Exhibits 7-2 through 7-4 indicate that system expansion requirements are much larger in urban areas than in rural areas, both in the total amount and as a share of overall investment requirements, under both investment scenarios.

System Enhancements

Investment requirements for system enhancements represent 7.9 percent of both the Cost to Improve Highways and Bridges ($8.4 billion) and the Cost to Maintain Highways and Bridges ($6.0 billion). Investment requirements for safety enhancements, traffic operation facilities, and environmental enhancements are not directly modeled, so this amount was derived solely from the external adjustment procedures described on the next page.

Cost to Improve Highways and Bridges, 2001-2020, Distribution by Improvement Type
Click here for text description of this exhibit.

Q.
Can highway capacity be expanded without adding new lanes or new roads and bridges?

A.
Yes. In some cases, highway capacity can be increased more cost effectively by improving the utilization of the existing infrastructure. Consequently, a portion of the investment requirements identified for “System Expansion” could also be met through increased investment in types of “System Enhancements” that also increase capacity. Some of the potential strategies for increasing effective highway capacity, including intelligent transportation systems, are discussed in Chapter 21. A limited number of these strategies have been incorporated into the calculations made by HERS (See Appendix A). Procedures for evaluating additional strategies have been developed, but could not be incorporated in HERS in time for this edition of the C&P report.

The methodology used to estimate system expansion requirements also allows high cost capacity improvements to be considered as an option for segments with high volumes of projected future travel that have been coded by States as infeasible for conventional widening. Conceptually, such improvements might consist of new highways or bridges in the same corridor (or tunneling or double-decking on an existing alignment), but the capacity upgrades could also come through other transportation improvements, such as a parallel rail line, busway, or mixed-use high occupancy vehicle/transitway. See Appendix A for more on this feature.

Sources of the Highway and Bridge Investment Requirements Estimates

The estimates of investment requirements for highways and bridges under the Improve and Maintain scenarios were derived from three sources:
  • Highway and bridge capacity expansion and highway preservation investments were modeled using HERS.
  • Bridge preservation investments were modeled using the NBIAS.
  • The HERS and NBIAS results were supplemented by external adjustments made to account for functional classes not included in the data sources used by the models, types of capital investment that are not currently modeled, and missing State data.
The model scenarios used in HERS and NBIAS to construct the Improve and Maintain scenarios are discussed in greater detail below. Exhibit 7-5 shows the sources of the highway and bridge investment requirements estimates.

Sources of the Highway and Bridge Investment Requirements Estimates (Billions of 2000 Dollars
Click here for text description of this exhibit.

The percentage of total investment requirements that are modeled in HERS is somewhat larger than was the case in the 1999 C&P report. The reason for this change is that investment requirements for new highway and bridge construction are now being directly modeled along with expansion of existing roadways, through the use of the high cost capacity improvements feature in HERS. This change is discussed in greater detail in Appendix A.

External Adjustments

External adjustments were made to the directly modeled improvements generated by HERS and NBIAS in two areas:

  • Highway functional classes. Bridges on all functional classes are represented in the National Bridge Inventory (NBI) database used by NBIAS, so all of the investment requirements for bridge preservation shown in this report are derived directly from NBIAS. However, the Highway Performance Monitoring System (HPMS) sample segment database used by HERS does not include rural minor collectors, rural local roads or urban local roads. Consequently, HERS does not provide estimates for these systems and separate estimates for highway preservation and system expansion were applied.
  • Improvement types. The improvement options that HERS and NBIAS consider primarily address pavement and capacity deficiencies on existing highway and bridge sections. Currently, HERS and NBIAS do not directly consider system enhancements. Estimates for this improvement type were applied across all functional classes.
The adjustment procedures assume that the share of total highway investment requirements represented by these functional classes and improvement types would be equivalent to their share of current highway capital spending. The amounts derived from these external adjustments are identified separately in this report, since they would be expected to be less reliable than those derived from HERS and NBIAS.

Q.
Why does the analysis assume that the share of future highway investments for non-modeled items would remain the same?

A.
No data are currently available that would justify an assumption that this percentage would change. If this percentage of highway capital expenditures used for rural minor collectors, rural and urban local roads, and/ or system enhancements were to rises in the future, then the investment requirements presented in this chapter would be understated. If this percentage falls over time, then the investment requirements shown would be overstated.

Adjustments for Missing State Data

A third adjustment was made to compensate for missing State data. The reliability of the investment requirement projections derived from the HERS model depends heavily on the accuracy of the HPMS sample data collected by States and reported annually to the FHWA. In some previous editions of this report, the HPMS data for certain States was not complete enough to be analyzed by HERS or its predecessor models, so some States were excluded from the analysis, and the national results were factored upward to compensate. Such procedures were not utilized in the production of the 1999 C&P report, as the data for all States was deemed sufficiently complete to be included in the analysis. This was possible in part because of major improvements to the HPMS software provided by the FHWA to the States. The software now includes a variety of new features to assist the States in improving the quality of their data submissions.

For this edition of the report, however, the data reported by one State in the 2000 HPMS did not include pavement condition data for those roads not under State jurisdiction. As a result, the HPMS data for that State did not represent a statistically valid sample of all roads within the State. Consequently, all 2000 HPMS sample data for that State were removed from the data used to run HERS for this report, and a separate analysis was conducted processing older HPMS data through HERS to derive an adjustment factor to supplement the results of the national analysis

Highway Economic Requirements System (HERS)

The investment requirements shown in this report for highway preservation and highway and bridge capacity expansion are developed primarily from HERS, a simulation model that employs incremental benefit/cost analysis to evaluate highway improvements. The HERS analysis is based on data from the HPMS, which provides information on current roadway characteristics, conditions, and performance and anticipated future travel growth for a nationwide sample of more than 113,000 highway sections. While HERS analyzes these sample sections individually, the model is designed to provide results valid at the national level, and does not provide definitive improvement recommendations for individual highway segments.

HERS initiates the investment requirement analysis by evaluating the current state of the highway system using information on pavements, geometry, traffic volumes, vehicle mix, and other characteristics from the HPMS sample dataset. It then considers potential improvements on sections with one or more deficiencies, including resurfacing, reconstruction, alignment improvements, and widening or adding travel lanes. HERS then selects the improvement with the greatest net benefits, where benefits are defined as reductions in direct highway user costs, agency costs, and societal costs. In cases where none of the potential improvements produces benefits exceeding construction costs, the segment is not improved. Appendix A contains a fuller description of the project selection and implementation process used by HERS.

Q.
Does HERS identify a single “correct” level of highway investment?

A.
No. HERS is a tool for estimating what the consequences may be of various levels of spending on highway conditions and performance. If funding were unlimited, it might make sense to implement all projects identified by HERS as cost-beneficial. In reality however, funding is constrained, and highways must compete for funding with other public sector priorities. The investment requirement scenarios in this chapter estimate the resources that would be required to attain certain levels of performance, but are not intended to endorse any specific level of funding as “correct.”

One of the key features of HERS as an economics-based model (introduced in the 1997 C&P report) involves its treatment of travel demand. Recognizing that drivers will respond to changes in the relative price of driving and adjust their behavior accordingly, HERS explicitly models the relationship between the amount of highway travel and the price of that travel. This concept, sometimes referred to as travel demand elasticity, is applied to the forecasts of future travel found in the HPMS sample data. HERS assumes that the forecasts for each sample highway segment represent a future in which average conditions and performance are maintained, thus holding highway-user costs at current levels. Any change in user costs relative to the initial conditions calculated by HERS will thus have the effect of either inducing or suppressing future travel growth on each segment. Consequently, for any highway investment requirement scenario that results in a decline in average user costs, the effective VMT growth rate for the overall system will tend to be higher than the baseline rate derived from HPMS. For scenarios in which highway user costs increase, the effective VMT growth rate will tend to be lower than the baseline rate. A discussion of the impact that future investment levels could be expected to have on future travel growth is included in Chapter 9. Appendix A includes a further discussion of how travel demand elasticity is implemented in HERS, as well as recent changes in the elasticity procedures to account for traffic diversion and segment length.

Q.
How closely does the HERS model simulate the actual project selection processes of State and local highway agencies?

A.
The HERS model is intended to approximate, rather than replicate, the decision processes used by State and local governments. HERS does not have access to the full array of information that local governments would use in making investment decisions. This means that the model results may include some highway and bridge improvements that simply are not practical due to factors the model doesn’t consider. Excluding such projects would result in reducing the “true” level of investment that is economically justifiable. Conversely, the highway model assumes that State and local project selection will be economically optimal and doesn’t consider external factors such as whether this will result in an equitable distribution of projects among the States or within each State. In actual practice, there are other important factors included in the project selection process aside from economic considerations, so that the “true” level of investment that would achieve the outcome desired under the scenarios could be higher than that shown in this report.

While HERS was primarily designed to analyze highway segments, and the HERS outputs are described as “highway” investment requirements in this report, the model also factors in the costs of expanding bridges and other structures, when deciding whether to add lanes to a highway segment. All highway and bridge investment requirements related to capacity are modeled in HERS; the NBIAS model considers only investment requirements related to bridge preservation.

Highway Investment Backlog

The highway investment backlog represents all highway improvements that could be economically justified for immediate implementation, based on the current conditions and operational performance of the highway system. HERS estimates that a total of $271.7 billion of investment could be justified based solely on the current conditions and operational performance of the highway system. Approximately 82 percent of the backlog is in urban areas, with the remainder in rural areas. About 58 percent of the backlog relates to capacity deficiencies on existing highways; the remainder results from pavement deficiencies.

Note that this figure does not include rural minor collectors, or rural and urban local roads and streets, because HPMS does not contain sample section data for these functional systems. The backlog figure also does not contain any estimate for system enhancements. Appendix A explains how the backlog was calculated.

Q.
How is the HERS model used to produce investment requirements estimates for the various funding scenarios?

A.
The HERS model selects projects on the basis of their benefits and costs as calculated within the model. HERS can thus assign a benefit-cost ratio (BCR) to each selected improvement. The total investment over the 20-year forecast horizon is then estimated by establishing a minimum BCR for all improvements implemented in a given model run. By varying the minimum BCR in different HERS runs and examining the output for different indicators, the user can then determine the level of investment that will achieve certain levels of condition and performance. It is important to note that these estimates represent the economically efficient levels of investment that would meet the targets, rather than the minimum amount of investment necessary to meet the same criteria.

HERS Investment Scenarios

Two HERS investment scenarios were developed in order to generate the HERS-modeled portion of the two highway and bridge investment requirements scenarios. The HERS portion of the Cost to Improve Highways and Bridges was drawn from the HERS Maximum Economic Investment Scenario, and the HERS Maintain User Costs scenario fed into the Cost to Maintain Highways and Bridges. Exhibit 7-6 shows the estimated investment requirements under the two HERS scenarios. The impact of the various levels of investment on user costs and other indicators of highway condition and performance is presented in Chapter 9.

    
Exhibit 7-6

HERS Investment Requirements Scenarios 2001-2020 (Billions of 2000 Dollars)
 
  AVERAGE ANNUAL INVESTMENT REQUIRED
SCENARIO/BENCHMARK TOTAL HERS-MODELED
Maximum Economic Investment
$106.9
$69.1
Maintain User Costs
$75.9
$48.4

The Maximum Economic Investment scenario is of interest mainly because it defines the upper limit of highway investment that could be economically justified. It was used to generate the highway preservation and system capacity expansion components of the Cost to Improve Highways and Bridges. In this scenario, all improvements with a benefit-cost ratio greater than or equal to 1.0 are implemented in HERS. While this scenario does not target any particular level of desired system performance, it would eliminate the existing highway investment backlog and address other deficiencies that will develop over the next 20 years due to pavement deterioration and travel growth. As shown in Exhibit 7-6, the average annual investment modeled by the HERS Maximum Economic scenario is $69.1 billion.

The second major highway investment requirement scenario in this report is the Maintain User Costs scenario. It was used to generate the highway preservation and system capacity expansion components of the Cost to Maintain Highways and Bridges. This scenario gives the level of investment sufficient to allow total highway user costs per vehicle miles traveled (VMT) at the end of the 20-year analysis period to match the baseline levels. Highway user costs include travel time costs, vehicle operating costs, and crash costs. The average annual investment modeled by HERS under this scenario is estimated to be $48.4 billion.

The Maintain User Costs concept was introduced in the 1997 C&P report to provide a new highway system performance benchmark based on economic criteria. It focuses on highway users, rather than the traditional engineering-based criteria, which are oriented more toward highway agencies. This scenario is also an important technical point in the operation of HERS, since the VMT growth rates in the model are partly dependent on changes in user costs, due to the operation of the travel demand elasticity feature. The impact on individual highway user cost components at this and other levels of investment are discussed in Chapter 9.

Q.
Why was the Highway Maintain User Costs scenario used to estimate the Cost to Maintain Highways and Bridges, rather than the Highway Maintain Conditions scenario, which was used in the 1999 C&P report?

A.
The change was made for several reasons. The first relates to the use of the NBIAS model for bridge investment requirements estimates in this report. The investment estimates produced by this model, which is more economics-based than previous bridge investment models, are more comparable to the highway scenarios and benchmarks based on economic indicators. Second, the Maintain User Costs scenario is more in line with the concept of maintaining both conditions and performance, as in the baseline Maintain scenario for transit investment outlined in this chapter. The Maintain User Costs scenario is also more consistent with the Cost to Maintain scenarios used in C&P reports up to 1997. Third, the definition of user costs has been improved to include delay due to incidents and the premium that travelers place on travel time reliability. Finally, the user cost concept has found increasing acceptance within the transportation community in recent years as a measure of conditions and performance from the vantage of system users, as was reflected in the feedback received at outreach sessions conducted after the release of the 1999 C&P report.

National Bridge Investment Analysis System (NBIAS)

The bridge investment requirements shown in this report are derived primarily from the NBIAS, which is summarized in this section. Appendix B provides a more comprehensive look at this approach. Although NBIAS was introduced in the 1999 C&P report, this edition is the first to use it as the primary model for estimating future investment requirements for bridge preservation.

NBIAS is the latest in a series of bridge models used by the FHWA and its partners. It replaces the Bridge Needs and Investment Process (BNIP) model, which estimated bridge investment requirements for the 1999 C&P report. Like BNIP, NBIAS is based on data from the NBI, which provides information on the characteristics and conditions of more than 525,000 bridges in the United States.

The internal logic of NBIAS is derived from the PONTIS Bridge Management System. PONTIS is licensed by the American Association of State Highway and Transportation Officials to 45 State departments of transportation. Because this approach relies on having element-level condition data, which is not currently contained in the NBI, NBIAS begins its analysis by synthesizing element condition data from the general bridge condition ratings that are available. NBIAS considers individual bridges for improvement and replacement needs, but the current version of the model analyzes maintenance, repair, and rehabilitation (MR&R) needs on an aggregate level, rather than looking at individual bridges.

NBIAS improves upon BNIP in several ways. NBIAS includes a benefit/cost screen, which filters out improvements that are not cost-beneficial within the 20-year funding horizon. NBIAS is also more accurate in evaluating bridge subcomponents and determining the value of routine repair and rehabilitation of bridge elements. Finally, NBIAS provides estimates that are more reflective of the way State and local transportation agencies undertake bridge management strategies.

Q.
How does NBIAS aggregate bridge data?

A.
Aggregation of bridge data is a prerequisite for NBIAS analysis. Instead of managing individual bridges, NBIAS groups them into a number of cells. Each cell represents a group of bridges with common modeling characteristics. The common characteristics are called strata, and the process of grouping the bridges is known as stratification. NBIAS considers four main stratification dimensions for a bridge: its functional system; whether it is part of the National Highway System; average daily traffic (ADT); and climate zone. There are 13 functional systems, two NHS categories, five ADT classes, and four climate zones, producing 520 cells of bridges with common modeling characteristics.

Bridge Investment Backlog

As defined in this report, the bridge investment backlog represents the cost of improving all existing bridge deficiencies, if the benefits of doing so exceed the costs. NBIAS, like BNIP, defines deficiencies broadly, and covers more than the structurally deficient and functionally obsolete categories defined in Chapter 3. NBIAS estimates that $54.7 billion of investment could be invested immediately in a cost-beneficial fashion to replace or otherwise address currently existing bridge deficiencies.

The $54.7 billion bridge investment backlog is substantially lower than the $87.3 billion backlog reported in the 1999 C&P. This is due to the use of benefit/cost analysis in the NBIAS model. NBIAS determines that the optimal time to address some bridge deficiencies may not be in the first year of a 20-year planning horizon; instead, improvements or replacements may be made at other points of the planning period. This is more consistent with the real world experiences of State and local transportation agencies, which deal with bridge deficiencies over a multi-year planning period.

Bridge Investment Requirements Scenarios

While modeling techniques have changed from the BNIP to NBIAS models, the investment requirements scenarios are defined similarly. Two scenarios are examined: the Eliminate Deficiencies and Maintain Backlog scenarios. The results are described in Exhibit 7-7.

The Eliminate Deficiencies scenario is the bridge component of the Cost to Improve Highways and Bridges described earlier in this chapter. Where it is cost-beneficial to do so, the Eliminate Deficiencies 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 estimated to be $9.4 billion, which is 8.8 percent of the $106.9 billion average annual investment required to improve highways and bridges over a 20-year period.

The Maintain Backlog scenario is the bridge component of the Cost to Maintain Highways and Bridges. The Maintain Backlog scenario identifies the level of annual investment that would be required so that the bridge investment backlog would not increase above its current level. Existing deficiencies and newly accruing deficiencies would be selectively corrected to minimize the investment required to maintain the same backlog of deficient bridges in 2020 that exists in 2000. The average annual investment required under this scenario is estimated at $7.3 billion, or 9.7 percent of the $75.3 billion average annual investment required to maintain highways and bridges over a 20-year period.

    
Exhibit 7-7

NBIAS Investment Requirements Scenarios 2001-2020 (Billions of 2000 Dollars)
 
SCENARIO/BENCHMARK AVERAGE ANNUAL INVESTMENT REQUIRED
TOTAL NBIAS- MODELED
Eliminate Deficiencies
$106.9
$9.4
Maintain Backlog
$75.9
$7.3

Q.
How do the 1999 NBIAS estimates compare with the BNIP estimates in the 1999 Conditions and Performance Report?

A.
NBIAS estimates higher investment requirements to maintain the backlog than does BNIP, but projects lower investment requirements to eliminate all deficiencies. To avoid costly replacements in the future, NBIAS recommends more investment in repair and rehabilitation. This is consistent with a sound bridge management and asset management strategy.

BNIP estimated that the average annual investment required under the Eliminate Deficiencies scenario between 1998 and 2017 would be $10.6 billion. For the same scenario, NBIAS estimates a $9.4 billion average annual investment between 2001 and 2020. Approximately $0.5 billion is the result of a reduction in the number of deficient bridges that has occurred since 1997. The rest is due to the application of a cost/benefit analysis. Some bridge improvements are not cost-beneficial within the 20- year funding horizon. This is an improved, more realistic way to model the way governments make bridge investments.

For the Maintain Backlog scenario, BNIP estimated an average annual investment of $5.8 billion between 1998 and 2017. For the same scenario, NBIAS estimates a $7.3 billion average annual investment between 2001 and 2020. NBIAS does a better job of identifying repair and rehabilitation actions that will become increasingly necessary as the average age of the Nation’s bridges increases.
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