Another update of the guide is forthcoming. In contrast to the current guide, which relied heavily on an empirical approach to derive its design equations, the NCHRP contract to update the guide by 2002 calls for the use of an approach that would more realistically characterize existing highway pavement usage and improve the reliability of designs. An Existing Pavement Design and Analysis Method Has the Potential to Improve Highways and Is Being Used by Others

An existing method called nonlinear 3D-FEM has the potential to significantly improve the design and analysis of highway pavement structures. Nonlinear 3D-FEM is considered by many experts to be superior to current design and analysis methods because values of stresses, strains, and pavement deflections can be calculated accurately from a variety of traffic loads—static, impact, vibratory, and moving mixes of traffic loads, including multiaxle truck/trailer loads both within and outside legal weight limits. A chief engineer of the Ohio Transportation Department further told us that the state was pleased with Battelle’s efforts to predict pavement response using the nonlinear method. Conclusions

The pavement design guide developed and updated by AASHTO over the years for designing and analyzing highway pavement structures is outdated. Objectives, Scope, and Methodology

The objectives of this review were to (1) describe the roles of the Federal Highway Administration (FHWA) and others in developing and updating the pavement design guide and (2) examine the use and potential of a computer analysis method known as the nonlinear 3 Dimensional-Finite Element Method (3D-FEM) for improving the design and analysis of highway pavements. To accomplish these objectives, we first reviewed the American Association of State Highway and Transportation Officials’ (AASHTO) highway pavement guide, which is being used by many state departments of transportation as an aid in designing and analyzing pavement structures, federally funded and otherwise.
Why GAO Did This Study

GAO provided information on the: (1) roles of the Federal Highway Administration (FHwA) and others in developing and updating the pavement design guide; and (2) use and potential of a computer analysis method known as nonlinear 3 Dimensional-Finite Element Method (3D-FEM) for improving the design and analysis of highway pavement structures.

What GAO Found

GAO noted that: (1) FHwA has worked cooperatively with the American Association of State Highway and Transportation Officials (AASHTO) in developing and updating the pavement design guide; (2) the current guide is slated to be updated by the year 2002 to better reflect the changing priority of rehabilitating the nation's highways rather than building new ones; (3) in contrast to the current guide, that many transportation experts believe is outdated, the new guide is expected to incorporate the use of analytical methods to predict pavement performance under various loading and climatic conditions; (4) sponsors believe that a new design approach will more realistically characterize existing highway pavements and improve the reliability of designs; (5) a promising analytical method to accurately predict pavement response is the nonlinear 3D-FEM; (6) only with accurate response data can one reliably predict pavement performance; (7) the use of this method has the potential to improve the design of highway pavements, which encompasses highway safety, durability, and cost-effectiveness, because values of stresses, strains, and deflections (pavement response) can be calculated accurately from a variety of static, impact, vibratory, and moving mixes in traffic loads; (8) several state departments of transportation, academicians, and scientists have pioneered the use of the nonlinear 3D-FEM and are using it to solve a variety of complex structural engineering problems, including the design and analysis of highway pavement structures; and (9) while this is a promising method for improving highway pavement design and analysis, GAO could find no evidence that it is being considered for inclusion in the current design guide update.