Highway Infrastructure

Transportation systems play a vital role in the nation's economy by facilitating the movement of people and goods. The United States has made significant investments in its transportation infrastructure. The Transportation Equity Act for the 21st Century directed GAO to evaluate and report to Congress on how the Department of Transportation (DOT) determines highway investment requirements using the Highway Economic Requirements System (HERS). To estimate future investment requirements, DOT's Federal Highway Administration (FHWA) uses the HERS computer model. In this report, GAO describes (1) the methodology the model uses to generate its estimates of the nation's highway investment requirements, (2) the strengths and the limitations of the model, and (3) the usefulness of the HERS estimates for deciding on federal investments in highway infrastructure. Among other things, GAO reports that (1) the computer model estimates investment requirements for the nation's highways by adding together the costs of highway improvements that the model's benefit-cost analyses indicate are warranted; (2) HERS has several strengths that make it a unique and reasonable tool for estimating a general level of national highway investments, but that it also has some limitations that affect the precision of its results; and (3) HERS can be useful as a general guide for the investment requirements of the nation's highways included in the model.

GAO noted that: (1) the HERS computer model estimates investment requirements for the nation's highways by adding together the costs of highway improvements that the model's benefit-cost analyses indicate are warranted; (2) in making its estimates, the model relies on extensive data on highway segments throughout the nation, such as pavement conditions and expected growth in traffic; (3) the model also uses information, such as vehicle operating costs and emissions' obtained from other sources; (4) the HERS model uses the data to: (a) project the future condition and performance of the highway system; (b) assess whether any highway improvements are warranted; and (c) select and implement appropriate improvements; (5) such improvements range from resurfacing a highway to adding lanes and are based on a comparison of the construction costs and the lifetime benefits of the improvement; (6) a major strength of the model is its ability to assess the relative benefits and costs associated with alternative options; (7) the model has limitations, however, in that it: (a) does not completely account for the effect of highway improvements on all other highways and modes of transportation; (b) does not fully account for the uncertainties associated with its methods, data, and assumptions; (c) relies on a computational shortcut to approximate the future lifetime benefits of an improvement; and (d) uses data that vary in quality; (8) HERS estimates can be useful as a general guide for the investment requirements of the nation's highways included in the model, and for assessing relative investment requirements over time; (9) nevertheless, limitations and uncertainties associated with making forecasts prevent the estimates from being a precise forecast of highway investment requirements; (10) FHwA includes the HERS estimates in its current report on the conditions and performance of the nation's highways, bridges, and transit systems; (11) in the report, however, FHwA does not clearly disclose the level of uncertainties in the HERS estimates; (12) furthermore, to derive a total estimate of highway investment requirements, FHwA combines the HERS estimates with estimates for other types of highways and investments that are not based on benefit-cost analyses; and (13) as a result, the report's readers are not likely to be aware of the imprecision of the HERS estimates and the fact that only part of the total highway investment requirements is estimated on the basis of an assessment of the benefits and costs of alternative improvement options.

Recommendations

Our recommendations from this work are listed below with a Contact for more information. Status will change from "In process" to "Open," "Closed - implemented," or "Closed - not implemented" based on our follow up work.

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