The authors developed a new ATP (Automatic Train Protection) system in Japan: the ATS (Automatic Train Stop) system. The new system called ATS-Dx is based on the ATS-X system which is interoperable with the existing ATS-S system already deployed on almost all JR company conventional lines. ATS-Dx guarantees an even higher level of safety than the ATS-S system because it includes a function to compare actual vehicle speed with a permissible speed profile calculated by an on-board equipment. The ATS-Dx system can also reduce construction costs and the number of beacons usually required for providing reference speed limits in curves and for turnouts by virtue of an on-board database. In this paper, the authors describe the system's specifications and the results from field trials to test this function.