What does UIC Leaflet 640 define?

UIC Leaflet 640 defines the technical conditions and calculation methods for the tractive effort of locomotives, ensuring standardized performance reporting across the rail industry.

What is the difference between starting and continuous tractive effort?

Starting tractive effort is the peak force used to move a train from rest (limited by adhesion), while continuous tractive effort is the force the motors can provide indefinitely without thermal damage.

Why is the adhesion coefficient important in UIC 640?

The adhesion coefficient determines the maximum force that can be transmitted to the rails without the wheels slipping, which is critical for safety and efficiency in heavy-haul and high-speed rail.

UIC Leaflet 640: Calculating the Pulling Power of Modern Locomotives

UIC Leaflet 640 defines the technical methods for calculating locomotive tractive effort. Master the formulas that determine a train’s pulling power and adhesion limits.

September 24, 2023 1:39 am

What is UIC Leaflet 640?

UIC Leaflet 640 is the authoritative technical document titled “Technical conditions with which leaf springs for vehicles must comply — Tractive effort.” It provides the standardized mathematical framework for determining the tractive effort of locomotives and power units.

In the railway industry, tractive effort is the force generated by the propulsion system at the wheel-rail interface to move the train. UIC 640 ensures that when a manufacturer specifies a locomotive’s “Pulling Power,” it is calculated using a methodology recognized by infrastructure managers and railway undertakings worldwide. This prevents discrepancies in load planning and ensures operational safety on steep gradients.

Core Technical Definitions

The leaflet distinguishes between several phases of traction, each critical for different operational scenarios:

Starting Tractive Effort: The maximum force the locomotive can exert at zero speed to overcome static friction and inertia.
Continuous Tractive Effort: The force that the traction motors can sustain indefinitely without overheating the electrical insulation or mechanical components.
Adhesion-Limited Tractive Effort: The physical limit of force that can be transmitted based on the friction between the steel wheel and the steel rail.

The Adhesion Factor

A central pillar of UIC 640 is the calculation of the Adhesion Coefficient. Even the most powerful motor is useless if the wheels slip. The leaflet provides empirical formulas to estimate the available friction under various weather conditions (dry, wet, or icy rails). It also accounts for the use of sanding equipment and electronic “creep control” systems that maximize the utilization of adhesion.

Comparison: Tractive Effort Types in UIC 640

Traction Phase	Limiting Factor	Operational Importance
Starting	Adhesion / Mechanical Strength	Ability to move a heavy freight train from a standstill.
Continuous	Thermal limit of Traction Motors	Maintaining speed on long, sustained gradients.
Maximum	Power Converter / Inverter Capacity	Short-term acceleration or peak performance needs.
High Speed	Available Power ($P = F \times v$)	Cruising at top speed where aerodynamic drag is high.

Impact on Timetable and Load Planning

Railway operators use the data derived from UIC 640 to determine “Load Tables.” By knowing the tractive effort curves of a locomotive, a dispatcher can calculate exactly how many tons of freight a single unit can pull across a specific mountain pass. Miscalculating these values according to UIC 640 standards can result in “stalled” trains, which block mainlines and disrupt the entire network.

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