The Long-Term Pavement Performance (LTPP) program has recently started a new Specific Pavement Study (SPS) experiment to compare the long-term performance of warm mix asphalt (WMA) technologies to conventional hot mix asphalt (HMA). This paper discusses the observations during the construction of the first two test sites, each consisting of a control HMA section and two WMA sections with the foaming and chemical additive technologies. In a preliminary analysis of the collected falling weight deflectometer (FWD) data before and after the overlay construction, the relationship between the mix laydown temperature and the resulting stiffness gain in the pavement structure was investigated. The equivalent pavement elastic modulus was estimated before and after overlay and the change in stiffness was contrasted between the HMA and WMA technologies. No specific trends could be inferred from this preliminary analysis. While the control section has gained more stiffness as a result of the HMA overlay compared to the other WMA overlays in one site, the chemical WMA section is demonstrating the highest gain in stiffness in the other site. Among the WMA sections, the average amount of added stiffness was higher for the foaming process in one site and for the chemical additive in the other. This suggests that the observed differences in the stiffness are predominantly a result of construction variability and cannot be attributed to the differences in mix and laydown temperatures. As performance monitoring and materials sampling and testing continues with time, further details might emerge regarding the long-term performance of warm mix technologies compared to each other and to the conventional hot mix.