Introduction: Understanding Railway Rail Classification

Railway rails are the backbone of modern transportation infrastructure. Whether you're an engineer specifying track components, a procurement professional sourcing materials, or simply someone interested in railway technology, understanding rail classification is essential.

Rails can be classified in two primary ways: by cross-sectional shape (the physical profile of the rail) and by function (where and how the rail is used on the track). This guide provides a comprehensive overview of both classification systems, complete with specifications and real-world applications.

Part 1: Classification by Cross-Sectional Shape

The cross-sectional profile of a rail determines its structural behavior, load-bearing capacity, and compatibility with other track components. Modern rails are hot-rolled steel of specific cross-sectional profiles. There are three primary shape categories:

1. Flat Bottom Rail ( Vignole Rail)

Definition: The flat bottom rail—also known as the Vignole rail—features a wide, flat base (foot) that sits directly on the rail sleepers (ties) and is secured with fastening systems.

Structure: A standard flat-bottom rail consists of three main components: the head (the top running surface for wheels), the web (the vertical connecting section), and the base or foot (the wide bottom flange).

Characteristics:

• Wide, flat base for stable fixation

• Asymmetrical "I" or "I" shape

• Directly fixed to sleepers using rail clips and pads

• Highest strength-to-weight ratio among rail profiles

Applications: This is the most commonly used rail type worldwide, employed in:

• High-speed passenger railways

• Heavy-haul freight mainlines

• Subway and metro systems

• General mixed-traffic corridors

Standards: Flat bottom rails are manufactured according to various international standards including AREMA (American), UIC (European), BS (British), DIN (German), and JIS (Japanese).

Common AREMA Sections: The most widely used AREMA flat bottom rail sections include 115RE, 132RE, and 136RE. These sections vary by weight and dimensional proportions to suit different traffic demands.

The choice between sections depends on axle load, annual tonnage, train speed, and curve radius. Heavier sections like 136RE and 141RE provide greater bending resistance and fatigue strength for demanding mainline service.

2. Bull Head Rail 

Definition: The bull head rail is an older design where the head and foot are similar in size and shape. Its name derives from the prominent, "bull-like" head that extends outward.

Structure: Unlike the flat bottom rail, the bull head rail has a nearly symmetrical cross-section with the head and foot being roughly equal in dimensions. It cannot stand independently on a flat surface and must be secured in cast iron chairs (rail bases) that hold the rail in position.

Characteristics:

• Symmetrical or near-symmetrical head and foot

• Requires specialized cast iron chairs for fixation

• Narrower web compared to flat bottom rails

• Lower stability than modern flat bottom designs

Historical Usage: The bull head rail was the standard in British railways for many decades. In general use, 95 lb/yd sections were employed on main lines, while 85 lb/yd sections served branch lines with lighter traffic.

Current Status: All new track is now laid with flat bottom rails. Bull head rails have been largely replaced by flat bottom (Vignole) rails for better performance and cost-effectiveness. Some legacy installations remain, particularly on heritage railways and in certain underground systems. For example, London Underground is in the process of replacing their bull head rails with BS113A flat bottom rails.

Typical Dimensions (95R BH):

3. Grooved Rail ( Grooved Tram Rail)

Definition: The grooved rail features a longitudinal groove in the head section, specifically designed to accommodate the wheel flanges of tram and light rail vehicles.

Structure: The rail head contains a continuous vertical slot (groove) that guides the wheel flange. When installed in city streets, the groove allows the flange to roll within the slot while the rail head surface remains flush with the roadway, minimizing interference with other road traffic.

Characteristics:

• Longitudinal groove in the rail head

• Flush installation with road surface

• Designed specifically for flange-guided vehicles

• Prevents interference with automobile and pedestrian traffic

Applications:

• Urban tram (streetcar) systems

• Light rail transit (LRT) networks

• City-center street tracks

Standards: Grooved rails are manufactured according to EN 14811 (European standard), which defines requirements for grooved rails with a linear mass of 42 kg/m and upwards for tram transport systems.

Typical Dimensions (59R2 Grooved Rail):

Part 2: Classification by Function

Beyond shape, rails are also categorized by their specific function on the track. These functional rails may have specialized profiles or be made from standard sections adapted for particular purposes.

4. Guard Rail ( Check Rail)

Definition: A guard rail (also called a check rail) is a rail placed parallel to the regular running rail to keep the wheels of rolling stock in alignment and to prevent derailment.

Function: Guard rails serve to align the wheels on railroad car axle sets, preventing damage to other trackwork components and ensuring that the wheel set tracks a particular path where a wheel may have a tendency to derail. The head portion of the guard rail is configured to contact the wheels to prevent them from slipping off the drive rail.

Applications:

• Turnouts (switches and crossings): Installed to guide wheels through complex track geometry

• Bridges: Provides additional protection against derailment on elevated structures

• Sharp curves: Reduces the risk of flange climb derailment

• Areas with high derailment risk: Where a derailment would present a particular safety hazard

Specifications: Guard rails are covered by standards such as BS EN 13674-3, which provides dimensions, tolerance measurements, and product quality requirements to ensure track safety. In China, grooved steel guard rails (槽型钢护轨) are commonly used in turnouts, with specifications such as 60 kg/m for turnouts with speeds up to 200 km/h.

Key Point: Unlike running rails, guard rails are normally not loaded by train wheels—they only come into contact with wheels during lateral movement or potential derailment scenarios.

5. Girder Rail ( Girder Rail)

Definition: A girder rail is a deep, heavy rail used for streetcars in cities, with a cross-section similar to that of an I-beam with a projection on top forming the tread of the rail.

Function: Girder rails serve a dual purpose: they function as both the running rail for vehicles and as a structural beam (girder) that supports the track structure. This is particularly important in bridge applications and elevated track sections.

Characteristics:

• Deep section with high vertical stiffness

• Combines rail and structural beam functions

• Often used on bridges and elevated structures

• May have a wider base than ordinary rails

Applications:

• Railway bridges: Where the rail itself contributes to the bridge's structural integrity

• Elevated railways: Supporting track on viaducts and overpasses

• Streetcar systems in cities: Particularly on curves

Historical Note: The term "bridge rail" was historically used for a shallow but wide section first laid on bridges on the Great Western Railway. Modern girder rails have evolved significantly from these early designs.

Summary: Complete Rail Classification Reference

Conclusion

Understanding railway rail classification is fundamental for anyone involved in track design, maintenance, or procurement. The three primary shape-based categories—flat bottom, bull head, and grooved—define the physical characteristics of the rail, while functional categories like guard rails and girder rails describe specialized applications.

Today, flat bottom rails (particularly AREMA sections like 115RE, 136RE, and 141RE) dominate global railway infrastructure, offering the best combination of strength, stability, and cost-effectiveness. Bull head rails, once the standard, have been largely phased out in favor of modern flat bottom designs. Grooved rails remain essential for urban tram networks, while guard rails and girder rails serve critical safety and structural roles in specialized track locations.

Whether you're specifying rails for a new high-speed line, maintaining an existing freight corridor, or designing an urban tram network, understanding these classifications will help you select the right rail type for your application.