Nowadays, the monitoring of railway signalling assets is conducted alternatively through human maintenance activities, wired solutions and active surveying by means of moving vehicles. However, these means present many limitations. RADIUS proposes to overcome these limitations by using Unmanned Aircraft Systems (UAS) or drones to execute a large part of the inspection and maintenance effort on-site. The RADIUS automation will also allow increased inspection frequency. Therefore, a new paradigm for railway inspection and maintenance shall be defined to limit activities carried out by human teams and to improve the global railway operational service in terms of availability, reliability and performance.