Why EN 15686 Changes European High-Speed Rail

Understanding EN 15686: Testing High-Performance Railway Vehicles

EN 15686 is a European standard that specifies the testing procedures for the acceptance of running characteristics for railway vehicles equipped with cant deficiency compensation systems (such as tilting trains) or those designed to operate safely at higher levels of cant deficiency than permitted by the general standard, EN 14363.

This standard serves as a crucial extension to EN 14363, which outlines the fundamental testing and approval processes for the running characteristics of all railway vehicles. EN 15686 addresses the unique dynamic behaviors and safety considerations of specialized rolling stock designed to navigate curves at higher speeds, thereby enhancing network capacity and reducing journey times on conventional lines.

Core Objectives and Scope of EN 15686

The primary goal of EN 15686 is to provide a standardized and reliable methodology for verifying the safety and performance of vehicles that operate beyond conventional dynamic limits. Its scope is highly specific, focusing on two main categories of vehicles:

• Vehicles with Cant Deficiency Compensation Systems: Commonly known as “tilting trains,” these vehicles have active or passive systems that tilt the carbody inwards on curves. This tilting action counteracts the centrifugal force experienced by passengers, improving comfort and allowing the vehicle to negotiate the curve at a higher speed.
• Vehicles Intended for Higher Cant Deficiency Operation: These are vehicles that, while not necessarily equipped with a tilting mechanism, are specially designed (e.g., with advanced suspension, lower center of gravity) to safely handle the increased lateral forces associated with operating at a higher cant deficiency.

The standard establishes clear procedures to ensure these vehicles do not pose a risk to track integrity or their own operational stability.

Key Technical Aspects and Testing Procedures

EN 15686 builds upon the on-track testing framework of EN 14363 but introduces additional requirements and assessment criteria tailored to the specific technologies involved. The testing process is rigorous and multifaceted, covering safety, track interaction, and ride quality.

On-Track Testing Methodology

The on-track tests are the cornerstone of the acceptance process. They involve equipping the vehicle with a suite of sensors to measure critical parameters while it operates over a carefully selected test track section with varying curve radii and track quality.

• Measurement of Forces: Key measurements include the lateral (Y) and vertical (Q) wheel/rail forces. The ratio of these forces (Y/Q) is a critical indicator for assessing the risk of wheel climbing and derailment. EN 15686 defines specific limit values for these forces under conditions of high cant deficiency.
• Vehicle Body and Bogie Accelerations: Lateral and vertical accelerations are measured on the vehicle body floor and bogie frames. These are used to assess passenger comfort (ride quality) and the dynamic loading on vehicle components. For tilting trains, the standard pays close attention to the residual lateral acceleration experienced by passengers after the tilt compensation is applied.
• Track Loading Assessment: The standard requires a thorough evaluation of the forces exerted by the vehicle on the track, including quasi-static and dynamic track-shifting forces. This is vital to ensure that the higher operational speeds do not lead to premature track degradation or compromise track stability.

Specific Tests for Cant Deficiency Compensation Systems

For tilting trains, EN 15686 mandates additional tests to validate the performance and reliability of the compensation system itself. These tests are designed to assess:

• System Response: The accuracy, speed, and smoothness of the tilting mechanism’s response to track curvature. This includes measuring the time lag between entering a curve and the system achieving the target tilt angle.
• Failure Modes: A critical part of the testing involves simulating failures of the tilting system (e.g., power loss, sensor failure) to ensure the vehicle remains safe in a degraded or non-tilting mode. The vehicle’s running characteristics are evaluated under these failure conditions.
• Transition and Reversal Curves: Special attention is given to the vehicle’s behavior in transition curves (where cant and curvature change) and S-curves, as these areas place the highest demand on the compensation system’s control logic.

EN 15686 vs. EN 14363: A Comparative Overview

While interconnected, these two standards serve different purposes. EN 14363 is the general, foundational standard for all vehicles, whereas EN 15686 is the specialized, supplementary standard for a specific class of high-performance vehicles.

The Importance of EN 15686 in Modern Railways

The implementation of EN 15686 is a key enabler for modernizing rail networks without requiring the cost-prohibitive reconstruction of existing infrastructure. By providing a safe and standardized path for the approval of tilting and high-performance trains, it allows operators to:

• Increase Speeds on Conventional Lines: Reduce journey times on routes with significant curvature.
• Enhance Passenger Comfort: Minimize the lateral forces felt by passengers, providing a smoother and more pleasant travel experience.
• Boost Network Capacity: Run more services or achieve better timetables by improving average speeds across the network.
• Foster Innovation: Gives manufacturers a clear and internationally recognized framework for developing and certifying advanced vehicle technologies.

Conclusion

In summary, EN 15686 is not a replacement for EN 14363 but a vital and highly technical extension. It addresses the complex dynamics of railway vehicles that push the boundaries of conventional operation. By defining rigorous testing procedures and strict safety criteria, the standard ensures that the pursuit of higher speeds and greater efficiency on curved tracks is achieved without compromising the fundamental principles of railway safety and reliability.