Conditions and Performance Report

Conditions and Performance Report
Chapter 7—Future Capital Investment Requirements

Conditions and Performance Chapter Listing

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Introduction

Summary

Economics-Based Approach to Transportation Investments

Highway Investment Requirements

Bridge Investment Requirements

Combined Highway and Bridge Investment Requirements

Transit Investment Requirements

Highway Investment Requirements

The highway investment requirements shown in this report are developed primarily from the High-way Economic Requirements System (HERS), a simulation model that employs incremental benefit/cost analysis to evaluate highway improvements. The HERS analysis relies on the Highway Performance Monitoring System (HPMS) to provide information on the current conditions and performance and anticipated future travel growth for a nation-wide sample of more than 120,000 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.


Q What is the reliability of the highway investment requirement projections made in this report?
A The HERS model is deterministic, rather than probabilistic, meaning that it provides a single predicted value rather than a range of likely values. Therefore, we can not make specific statements about confidence intervals. However, we can make some general statements about the limitations of the projections, based on the characteristics of the process used to develop them. As in any modeling process, simplifying assumptions have been made to make analysis practical, and to meet the limitations of available data. Potential highway improvements are evaluated based on a benefit/cost analysis. However, this analysis does not include all external costs, such as noise pollution, or external benefits, such as the favorable impacts of highway improvements on system reliability, and on the economy. To some extent, such external effects cancel each other out, but to the extent that they don't the "true" investment requirements may be either higher or lower than those predicted by the model. Some projects that HERS views as economically justifiable may not be in reality. Other projects that HERS would reject might actually be justifiable, if all factors were considered.

The HERS results are supplemented by external adjustments to account for functional classes not included in the HPMS database, and for types of capital investment that are not currently modeled. This procedure has been streamlined for this report, replacing some old procedures originally developed to supplement the HPMS Analytical Process, that are not fully compatible with the new HERS approach. The external adjustment process has also been expanded to account for all types of highway capital investment. In previous reports, some types of improvements were not included in the reported investment requirements. These 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.

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 separate bridge models consider only investment requirements related to bridge preservation.

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Page last modified on November 7, 2014