The Pennsylvania Department of Transportation (PENNDOT) is sponsoring the Superpave In-Situ Stress/Strain Investigation (SISSI), which will complete its fifth year in May, 2006. The purpose of the SISSI project is to provide data essential to the validation and regional calibration of Superpave and the new Mechanistic-Empirical Pavement Design Guide (MEPDG). SISSI is a unique, state-of-the-art instrumentation and analysis project that encompasses eight different Superpave pavement sections across Pennsylvania, including both new pavements and overlays. The uniqueness of the SISSI project is that the selected pavement sections were instrumented as-designed and as-constructed on full-scale public highways, to represent actual practices and materials, without modification for this research, and with minimal interruption to the construction process. The sections are exposed to normal traffic, but evaluated seasonally and yearly using a loaded test vehicle. The project also takes advantage of the latest developments and equipment in the field of instrumentation technology for the full-scale investigation of pavement performance. The project includes detailed monitoring of the construction process, intensive materials characterization, detailed load-response information, traffic and environmental data, and performance measures. This paper briefly reviews the instrumentation and data collection at the eight sites. Examples are provided of the data acquired from the instrumentation, and the interpretation of that data. Data examples are included from the dynamic gauge responses under the controlled truck loading and corresponding WIM (weigh-in-motion) analysis, and from the subsurface environmental gauges.