For Paris-Nord, a busy railroad station, routing traffic and allocating platforms to trains is a complex process. Every day, Paris-Nord planners at the French National Railway Company (SNCF) handle over 1,700 trains sharing 300 kilometers of network - a combination that can generate up to 400,000 itineraries. Many constraints must be analyzed in order to route traffic properly. This is a time-consuming task which has so far been done manually by a team of 15 planners using pen and paper.

 With an ever increasing traffic load - principaly due to high speed TGV trains and the Eurostar shuttles between London and Paris - SNCF has turned to constraint programming technology to help its planners face this new challenge. Today, Sagitaire, the new system developed with ILOG Solver, cuts weeks off the tedious process of scheduling trains and helps SNCF draw up timetables which route traffic safely, smoothly, and efficiently.

Flexibility for rapidly evolving changes
Planning and routing trains at Paris-Nord is a typical over-constraint problem, where no solution can satisfy every constraints placed upon the system. Given all the trains, network conditions, and platform information, Sagitaire automatically generates a schedule that breaks as few constraints as possible.

Schedules are updated regularly. Six times a year, SNCF adjusts them to include vacations and daylight savings time. Minor changes, such as the presence of a VIP or local strikes, are taken into account each day.

In order to smooth user transition from the old pen-and-paper method to computer-assisted planning, Sagitaire displays information graphically in a format familiar to planners. Users are also able to point and click the screen to modify Sagitaire's suggested schedule, applying their preferences and making use of their expertise.

 Validated schedules are used to handle tasks ranging from switching devices to automatic display panels in the station.

Designed to adapt to any kind of new constraints at Paris-Nord, Sagitaire can be easily customized for other railroad stations.

Benefits

ILOG Solver has reduced design and planning of new schedules from a few days to less than an hour, and has drastically improved replanning time. Above all, Sagitaire's interactive and user-friendly graphic environment manages all the routine work and lets SNCF planners concentrate on the task that requires most of their expertise - difficult planning situations.

Project
Developed by the software house Ingenia and a small SNCF team of one planner and two engineers from the station's MIS department, Sagitaire runs on a Sun Microsystems Sparc workstation. Train information and updated schedules are available from an Ingres database. Schedules are drawn automatically by Sagitaire using the Autocad CAD tool.

With more than 58 billion passengers per kilometre anually, and 182,000 employees, SNCF is one of the largest railroads in the world. The French company offers services ranging from the TGV high-speed lines and Eurostar trains to freight and parcel services. SNCF's future is significantly linked to European construction, and the company has signed many cooperation agreements with other European nations.