UIC Leaflet 491: Technical Conditions for the Transport of Road Vehicles on Wagons

What is UIC Leaflet 491?

UIC Leaflet 491 is the primary standard for “Piggyback” transport, titled “Technical conditions for the transport of road vehicles on wagons.” As a pillar of Combined Transport, it bridges the gap between road and rail by providing the rules for loading semi-trailers and trucks onto specialized Rolling Stock.

The central challenge addressed by UIC 491 is the Gauging problem. Because road vehicles are often taller than standard rail containers, they risk striking trackside structures. This leaflet provides the mathematical and physical framework to ensure Clearance throughout the journey.

The Codification System (The “P” and “C” Codes)

To simplify international operations, UIC 491 established a coding system that allows terminal staff to quickly determine if a specific trailer can travel on a specific route:

• Profile Number (e.g., P400): A code assigned to a semi-trailer based on its height and width when loaded on a standard wagon. A “P400” trailer requires a route cleared for a 4.00-meter height profile.
• Route Compatibility: Infrastructure Management authorities code their lines (e.g., a line might be “C-coded” for swap bodies or “P-coded” for trailers).
• The Yellow Label: Every intermodal unit must have Wagon Labeling (or unit labeling) that displays this code, ensuring that the rail operator can verify the “loading envelope” at a glance.

Technical Requirements for Pocket Wagons

UIC 491 defines the design criteria for the wagons used in this service, particularly Pocket Wagons (wagons with a “well” or “pocket” to house the trailer’s wheels):

• Securing Devices: Requirements for the “hitch” (kingpin support) that locks the semi-trailer onto the wagon to prevent shifting during emergency Brake Application.
• Wheel Recesses: Dimensions for the pockets to ensure that the trailer sits as low as possible to the rail, maximizing Clearance.
• Lateral Stability: Limits on the center of gravity height to prevent derailment in curves or high winds.

Operational Safety and Clearance

The leaflet ensures Operational Safety by mandating:

• Inflation State: Rules regarding the air suspension of the road trailer, which must be deflated to a specific level during transport to maintain a constant height.
• Tarpaulin Security: Requirements for securing soft-sided trailers to prevent “billowing” which could violate the kinematic gauge and strike passing trains.

Comparison: Semi-Trailer (P-Code) vs. Swap Body (C-Code)