Abstract: A car space measurement apparatus for tracking a rail vehicle position on a track is provided, which includes a wayside sensor and a supervisory processor. The wayside sensor senses multiple track parameters that are representative of the rail vehicle position. The supervisory processor receives selected track parameters and determines the rail vehicle position therefrom. Also the supervisory processor asynchronously displays a track position indication representative of the rail vehicle position. The apparatus can have an operational mode, a calibration mode, and a self -test mode. The selected track parameters are analog track phase signals. The supervisory processor can include an analog signal processor, a phase processor for determining the track position indication and a control processor for asynchronously receiving and displaying the track position indication. The asynchronous interface can be a asynchronous computer bus interface.