The Capacity Calculator: Mastering Railway Efficiency with UIC 406

UIC Leaflet 406, titled “Capacity,” is the definitive industry standard for defining, calculating, and analyzing railway infrastructure capacity. Unlike simple train-counting methods, UIC 406 treats capacity not as a fixed number, but as a dynamic variable dependent on the timetable structure. It introduces the “Compression Method,” a standardized technique to measure how much of the track’s potential is currently being consumed and how much “spare capacity” remains for additional trains.

The Core Methodology: Timetable Compression

The heart of UIC 406 is the compression method. To calculate capacity consumption, existing train paths in a timetable are pushed (compressed) as close together as the signaling system allows, removing all unnecessary wasted time between them. The remaining time in the hour or day represents the theoretical spare capacity.

Key Definitions in Capacity Analysis

• Occupancy Time: The actual time a specific track section is occupied by a train sequence, including the time required for signal clearance.
• Buffer Time: Additional time added between trains to absorb minor delays and prevent knock-on effects (secondary delays).
• Capacity Consumption: A percentage value derived from dividing the compressed occupancy time by the total reference time (usually peak hours).

Types of Capacity: Theoretical vs. Practical

UIC 406 distinguishes between what is mathematically possible and what is operationally viable. The table below breaks down these layers of capacity:

The Impact of Heterogeneity

UIC 406 highlights that capacity is heavily influenced by the mix of trains (Heterogeneity). A line running only metro trains at constant speeds has high capacity. A line mixing fast Intercity trains with slow heavy freight trains loses capacity because large gaps (headways) are needed to prevent the fast trains from catching up to the slow ones. UIC 406 provides the formulas to quantify this loss.