The Transportation Equity Act for the 21st Century (P.L. 105-178) directed the General Accounting Office to evaluate and report to the Congress how the Department of Transportation determines highway investment requirements using the Highway Economic Requirements System (HERS) computer model. Accordingly, this report describes (1) the methodology the model uses to generate its estimates of the nation's highway investment requirements, (2) the strengths and limitations of the model, and (3) the usefulness of the HERS estimates for deciding on federal investments in highway infrastructure. Briefly, 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. 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, which the states primarily collect and update. The model also uses information, such as vehicle operating costs and emissions, obtained from other sources. A major strength of the model is its ability to assess the relative benefits and costs associated with alternative options for improving the nation's highway infrastructure. The model has limitations, however, in that it (1) does not completely account for the effect of highway improvements on all other highways and modes of transportation; (2) does not fully account for the uncertainties associated with its methods, data, and assumptions; (3) relies on a computational "shortcut" to approximate the future lifetime benefits of an improvement; and (4) uses data that vary in quality. HERS estimates can be useful as a general guide for the investment requirements of the nation's highways included in the model, such as rural and urban interstates, and for assessing relative investment requirements over time. Nevertheless, the limitations and inherent uncertainties associated with making forecasts prevent the estimates from being a precise forecast of highway investment requirements.


  • English

Media Info

  • Features: Appendices; Figures; Tables;
  • Pagination: 38 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00797087
  • Record Type: Publication
  • Report/Paper Numbers: GAO/RCED-00-133
  • Files: NTL, TRIS
  • Created Date: Aug 3 2000 12:00AM