As cities mature in Japan, 10,000 road cave-ins occur annually in urban areas, becoming a serious social problem. In order to solve the problem, industry, government, and academia carried out collaborative research over 2018-2020. In this joint research, analysis of existing cavity data, laboratory model experiments, numerical analysis, and full-scale field test, monitoring of the cavity in the road, etc. were conducted. In this study, a full-scale test road was constructed, with artificial cavities installed to evaluate the risk of collapse in consideration of the road structure and to develop repair methods. A series of FWD tests as well as plate loading tests were conducted on the road surface above the cavity to elucidate the cavity behaviour. Road surface conditions were monitored for more than a year. The cavity loading tests showed a correlation between the cavity depth and the pavement bearing capacity. The pavement is on the verge of sinking as the roadbed erodes and thins and the cavities approaches the asphalt layer. In this case, the surface collapses on a daily basis in the summer and on a monthly basis in the winter. This means that the risk of cave-in can be assessed as the ratio between the cavity depth and the cavity width. The thickness of the asphalt layer is therefore reasonable to exclude when assessing the risk of cave-in as the ratio of the cavity depth to the cavity width. The results suggest that FWD on pavements is highly dependent on road surface temperature and is not always effective in detecting sub-surface voids, even when temperature compensation is applied.