The nondestructive mapping of anomalies and voids under roadway pavements is critical to highway authorities because of the potential loss of support that would lead to safety hazards. 400 MHz ground-coupled penetrating radar (GCPR) was used in this study to characterize the subsurface conditions of three roadway pavements (SH359, IH40, and U.S. 290). The extents of the anomalies in horizontal and vertical directions were visible in GCPR images. Coring, boring, and lab testing were performed to verify the settlement and source of the moisture on SH359. The source of the moisture was from the leaking water pipe, as indicated by the high chloride and chlorite contents. A 1.8-m deep void (3.8 m3 in volume) under IH40 and a 1.8 m4.6 m3.7 m (30.6 m3 in volume) void under U.S. 290's reinforced concrete pavements were successfully identified by GCPR and verified by field boring and coring. Fortunately, the voids near the drainpipes were detected by GCPR in time. Otherwise, the void would have increased in size, and that could have led to a severe hazard. This study has successfully demonstrated that the GCPR is able to identify anomalies and voids. Therefore, engineers can utilize the information from GCPR to undertake remedial actions with confidence. 2010 ASCE.