Siemens AG R&D cooperated with Deutsche Bahn AG on railway station scheduling with AI methods and implemented a prototype capable of performing the day-to-day scheduling of a typical large station in Germany. The station chosen for this prototype is a large through station with 14 tracks and 6 platforms and a traffic flow rate of 68 trains per hour.

The computer system reacts to real-time scheduling problems which occur when trains are delayed; it then reschedules the arrivals minimizing the overall disruptance to the pre-planned timetable.




The interactive tool also allows controllers to adjust the schedule to meet other station activities. For example, track and platform maintenance may be specified which may close portions of the network for several hours. Alternatively, non-scheduled arrivals may be added to the schedule and their priorities defined.

The figure above shows a portion of the sheduled timetable for the station. Platform numbers corresponding to the lettered platforms are indicated on the x-axis. Time is indicated on the y-axis. The illustration here shows a smaller portion of the timetable than is actually interpretable on a large monitor screen. Scheduled trains may arrive from either end of the station, as indicated by the tags from- or to- the -left or -right; each train is also given a code. Known delays to certain trains are indicated below the trains arrival time.

In reality, three station controllers are responsible for the real--time allocation of incoming trains to platforms at this station. Their task is to minimise the number of passenger movements (where passengers must cross from their planned platform to a new platform), give priority to certain trains and also comply with all safety criteria.

The computer system models all aspects of the station and aims to assist the station controllers with the whole task. By specifying constraints that must be met in determining a new schedule the system searches for a good
solution.

Many established rules and safety regulations specify fixed constraints: governing, for example: the time a crossing must remain empty to ensure the train has passed. These fixed constraints may not be broken in the new computed schedule.

Other, more flexible constraints specify the minimum time a train should remain at a platform, which is less than the pre-planned time.

The application computes the new schedule based on the amendments from the station controllers and the delays to certain trains. These time and allocation constraints restrict the timetable; the schedule must compensate by reducing the time trains remain at platforms or by delaying other trains or in the worst case by allocating train and passengers to another less loaded platform. Passenger movements where passengers must simply cross to the other side of the same platform are less disruptive than those where passengers must use the subway.

Hardware: UNIX Workstation.
Software: IF/Prolog 5.0 with: Constraint Technology Package &