Abstract: A railroad signal system interlocking is automatically tested. A control point interface corresponding to a predetermined function of the interlocking has an isolated section and a control section. The isolated section is connected with the interlocking and has a normal, inactivated state during operation of the interlocking, and an activated state for testing the interlocking by detecting an electrical characteristic representing the status of the predetermined function executed by the interlocking. The control section drives the isolated section to its activated state and receiving an output from the isolated section in response to the detected electrical characteristic, and delivers a status report.