In 1994-96, the Ohio Department of Transportation (ODOT) constructed a 3.5-mile long test pavement on US 23 in Delaware County for the Strategic Highway Research Program. This project contained a total of 40 test sections of asphalt concrete and Portland cement concrete pavement in the SPS-1, SPS-2, SPS-8 and SPS-9 experiments of the Specific Pavement Studies program. These experiments were designed to assess the effectiveness of different base types and thicknesses, different pavement thicknesses and other design parameters on the structural performance of highway pavements. During the construction of these sections, the Falling Weight Deflectometer (FWD) was used to measure the composite stiffness of the sections as each new material layer was completed and accepted by ODOT. In addition, the Dynaflect trailer was used to measure the composite stiffness of the completed sections prior to their being opened to traffic. The overall objectives of this research study were to evaluate the stiffness of the test sections on this experimental pavement as the new material layers were added to the sections, and to evaluate various analysis software packages currently available for the backcalculation of layer moduli. While the Ohio SHRP Test Road was constructed in an area of flat terrain believed to have relatively uniform subgrade, FWD measurements indicated considerable subgrade variability between sections and within individual sections. None of the subgrade sections was considered to be good, about half were fair and the other half were poor to very poor. As expected, much of the variability was mitigated as successive material layers were placed in the sections, and especially with the addition of stabilized materials. Stiffness equivalencies were developed for the six types of base material used on the test road, and for AC and PCC pavement used on these bases. The final stiffness of the completed sections was consistent with early performance, in that the first six asphalt concrete sections which failed had the highest measured deflections with both the FWD and Dynaflect just prior to being opened to traffic. An excellent correlation was developed between FWD and Dynaflect output on the completed asphalt concrete pavement sections and clear trends were also apparent on PCC pavement, though the limited range of readings on PCC with both devices made it difficult to develop a definitive correlation on rigid pavement. The stiffness of the completed AC and PCC pavement sections, and load transfer across PCC pavement joints were quite similar when measured with the FWD and Dynaflect, demonstrating the usefulness of both instruments in evaluating structural performance. Four elastic layer programs were evaluated for their ability to calculate the moduli of the various material layers in the 40 test sections. Of these, MODULUS 4.2 performed the best and was the most user friendly program to run. To obtain consistent results on any specific project, a standard operating procedure needs to be developed for those conditions and the analysis program being used, and the procedure needs to be closely followed for all calculations.