Measuring deviations from schedule

At the Zurich dispatching center, both the time-distance display and the track-diagram display show the identifying number of each train and the number of minutes it is late (+) or early (-). The punctuality display has only two characters, so if a train is less than 10 minutes late it appears as in "09" but if 10 or more minutes late it appears as two digits, as in "23". If the display shows a schedule deviation of two plus signs ("++"), this means the train is more than 99 minutes late.

If the train is running early by less than 10 minutes, this appears as in "-8", and if 10 or more minutes early, as two minus signs: "--".

The following is a train on the track-diagram display in the Zurich dispatching center. It is moving eastbound through Schlieren station. Is it early or late?

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Drivers follow schedules that state the time at which they should pass stations and junctions. However, the system has a more detailed schedule prescribing the time of passage at each signal. The system compares this scheduled time with the actual time at which a train reaches a given signal (or more precisely, when the train enters the next block downstream), and updates the late/early indicator on the displays accordingly.

This is helpful in keeping an accurate view of the situation, as each driver drives differently in terms of where and how fast he accelerates and brakes, even if he sees nothing but clear signals.