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Conditions and Performance Report
Appendix G—Changes in Highway Investment
Requirement Methodology

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Introduction

Summary


Effect of Inflation

Expanding the Scope of the Investment Requirements

Data Corrections, Changes in Analytical Procedures and Model Enhancements

 

Introduction

The projected average annual highway investment requirements for 1998-2017 shown in this report are not directly comparable to those shown for 1996-2015 in the 1997 C&P report. Since the release of the "1997 Status of the Nation's Surface Transportation System—Condition and Performance" (C&P Report), the FHWA has conducted a series of outreach meetings with members of the academic community, congressional staff and other transportation professionals on the report and the HERS model. As a result of this process, the FHWA has reevaluated several of the procedures used in the development of previous reports.

As discussed in the introduction to Chapter 7, in previous C&P reports, separate external adjustments were made to account for some types of capital improvements, but other improvement types were omitted completely. Based on recommendations received during the C&P report outreach process, in this report, the scope of the investment requirements has been streamlined, and expanded to cover all types of highway capital outlay.

During the preparation of the last report, the State travel forecasts for some highway sections were manually reduced to match MPO forecasts. During this process, some errors were inadvertently introduced into the highway database that had an effect on the results, primarily for the Maximum Economic Investment scenario. The Maintain User Costs scenario results were also affected, but to a lesser degree. When these data issues were resolved, it became apparent that they had been masking some undesirable interactions between the new travel demand elasticity features in HERS, and some HERS settings and external adjustment procedures that had previously been in place. To address these problems, a number of changes have been made to the analytical procedures used to develop the investment requirements in this report. The "high cost lane" feature in HERS, that allowed the model to consider adding lanes in locations where it normally would not be feasible has been turned off. Some external model adjustments that formerly offset some of the high cost lanes have been eliminated, or folded into the streamlined adjustment process mentioned above.

Based on the recommendation of an expert panel that reviewed the HERS model, the emissions cost module in HERS has been utilized in this report, so the benefit cost analysis now considers this factor. The travel demand elasticity values used have also been increased. This change suppresses some travel demand in congested urbanized areas, which offsets an increase in the base VMT forecasts used in this report.

Some other modifications have been made to the HERS model that also have an impact on the results, most notably the development of new safety analysis procedures. The new procedures make increased use of specific highway characteristics affecting safety, and better reflect the effects of highway improvements on safety.

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