Railroad Rail Size and Clip Specifications

When engineers and track maintenance professionals discuss railroad rail size, they are rarely referring to length alone. In the railway industry, size is a function of weight and cross-sectional geometry, critical factors that determine a track’s capacity to handle modern freight and passenger loads. The term specifically relates to the weight of the rail per unit of length—pounds per yard in the Imperial system or kilograms per meter in the metric system. Understanding this weight-to-performance ratio is fundamental because the correct rail profile dictates everything from maximum axle load to the selection of compatible fastening components like rail clips.

Selecting the wrong profile or misidentifying an existing railroad rail size can lead to catastrophic failures or costly maintenance issues. A rail designed for light industrial use cannot withstand the dynamic forces of a heavy-haul coal train. Similarly, the fastening systems—specifically the rail clips—must be precision-engineered to match the specific geometry of the rail foot. If the clip does not fit the rail base width perfectly, the clamping force will be insufficient, leading to gauge widening or rail rollover. This guide delves deep into the specifications of rail sizes and the corresponding clips that secure them.

Railroad Rail Size by Weight and Section

Weight as the Primary Indicator

The most immediate way to classify rail is by its weight. When you hear terms like “136 lb rail” or “60 kg rail,” this refers to the mass of the steel. In North America, the standard nomenclature uses pounds per yard (lbs/yd). For example, a 115 lb rail weighs 115 pounds for every three feet of length. Internationally, and increasingly in modern engineering projects, kilograms per meter (kg/m) is the standard.

Historically, lighter rails such as 60 lb, 80 lb, or 85 lb sections were common. You might still find these on short lines, in mining operations, or on older sidings that see infrequent traffic. However, as locomotive power and freight car capacities have increased, the railroad rail size has evolved to keep pace. Modern Class I railroads in North America typically rely on heavy-haul sections ranging from 115 lb to 141 lb. These heavier sections provide greater vertical stiffness and beam strength, which spreads the immense load of the wheels over a larger area of the ballast and subgrade, reducing track degradation.

Section Profiles (ASCE, RE, UIC)

Weight is only half the story; the distribution of that weight—the profile—is equally important. Different engineering bodies have established standard profiles that optimize the rail’s shape for specific applications.

• ASCE (American Society of Civil Engineers): In the late 19th and early 20th centuries, the ASCE established a series of rail sections (e.g., ASCE 60, ASCE 85). These profiles are characterized by relatively uniform proportions between the height and the base width. While largely obsolete for mainlines, they remain prevalent in industrial tracks, crane runways, and light rail applications.
• RE (AREMA): The American Railway Engineering and Maintenance-of-Way Association (AREMA) maintains the current standard for North American rail. “RE” stands for “Railroad Engineering.” Profiles like 115 RE, 132 RE, and 136 RE are the workhorses of the continent. They feature a “T” rail design with a thicker web and a specific head radius designed to minimize contact stresses with the wheel.
• UIC (International Union of Railways): The UIC standards dominate outside North America. Profiles like UIC54 and UIC60 are standard for high-speed and heavy-haul networks in Europe, Asia, and Africa. These sections are optimized for stability and often feature a slightly different head curvature compared to RE rails.

Rail Size Chart for Proper Identification

In the field, you may encounter rail that is rusted, worn, or lacking clear manufacturer stamps. In these cases, physical measurement is the only reliable method for identification. To determine the railroad rail size, you need to measure four key dimensions:

1. Height: The vertical distance from the flat bottom of the base to the highest point of the rail head. This is often the most distinct differentiator between similar weights.
2. Head Width: The measurement across the widest part of the rail head. Wear on the running surface can slightly alter this, so measuring at the full width is crucial.
3. Base Width: The measurement across the bottom flange. This dimension is critical for selecting tie plates and rail clips.
4. Web Thickness: The thickness of the vertical “stem” of the rail at its thinnest point.

Reading Rail Markings

Before breaking out the calipers, check the web of the rail for rolled-in brands. Manufacturers roll raised characters into the web during production. These markings typically follow a standard sequence: Weight, Section, Manufacturer, Year, and Month. For example, a marking might read “136 RE CC TN 2021 /////”. This translates to a 136 lb RE section, Control Cooled, manufactured by Tennessee (generic example) in May of 2021 (indicated by the slashes). Interpreting these codes saves time and ensures 100% accuracy in identification.

Standard Railroad Rail Dimensions

The following table provides the dimensional specifications for the most common rail sections found in service today. Use this data to cross-reference field measurements against known standards.

Note: Metric conversions are approximate for general reference; always consult specific engineering drawings for tolerance-critical applications.

Rail Clips Specifications for Different Rail Sizes

The integrity of the track structure depends not just on the rail, but on how securely that rail is fastened to the sleeper (tie). This is the job of the rail clip. It is a critical error to assume that rail clips are universal. The specification of the clip must correspond directly to the railroad rail size, specifically the geometry of the rail foot (base).

Matching Clips to Rail Feet

The primary interface between the clip and the rail is at the toe of the clip, which sits on the rail base. If the rail base is wider or narrower than the clip design allows, the clip will not seat correctly in its housing or on the shoulder. This misalignment results in incorrect toe load (downward pressure). Too little pressure allows the rail to creep longitudinally; too much pressure (or uneven pressure) can overstress the clip, leading to fatigue failure.

Common Clip Types and Sizes

Different rail sizes require different clip models to maintain the necessary clamping force.

E-Clips (Elastic Clips)

The “E-Clip” is a staple in the industry, known for its distinct shape. These clips are driven into a shoulder that is cast into concrete ties or welded onto steel plates.

• Small Section Rails (e.g., ASCE 60): Lighter rails require smaller clips such as the E1609 or E1809. These provide sufficient holding power for lighter loads without being excessively difficult to install on smaller rail bases.
• Heavy Haul Rails (e.g., 136 RE): For standard heavy-haul applications, larger clips like the E2055 or E2007 are standard. These are manufactured from thicker bar stock (typically 20mm diameter) to generate the high clamping forces (around 2,500 lbs per clip) needed to restrain heavy rails under massive dynamic loads.

SKL Tension Clamps

Common in Europe and on tracks utilizing UIC rail sections, the SKL system (e.g., Vossloh fastening) uses a screw-tensioned clip.

• SKL 12 / SKL 14: These are frequently paired with UIC 54 and UIC 60 rails. They offer a high degree of elasticity and are particularly effective at maintaining gauge in high-speed rail applications where vibration is a significant factor.

Material and Force Specifications

Regardless of the shape, the material science behind the clip is vital.

• Material: High-quality clips are forged from spring steel, commonly grade 60Si2MnA. This silicon-manganese alloy is heat-treated to achieve a hardness of HRC 44-48. This ensures the clip retains its “spring” memory—it can flex under the passing of a train millions of times without permanently deforming or snapping.
• Toe Load: This is the measure of the downward force the clip exerts on the rail foot. For a heavy railroad rail size like 136 RE, the specification typically demands a toe load of 11-12 kN (approx. 2,500 – 2,700 lbf). This force is non-negotiable; it is what prevents the rail from tipping over (rollover) during cornering and stops the rail from sliding forward or backward due to thermal expansion and braking forces.

Frequently Asked Questions (FAQs)

Q1: How is railroad rail size measured?
A: Railroad rail size is primarily measured by its weight per unit of length—pounds per yard in the US, or kilograms per meter internationally. Additionally, the cross-sectional dimensions (height, base width, and head width) identify the specific profile type.

Q2: What is the most common railroad rail size?
A: For modern mainlines in North America, 132 lb and 136 lb rail are the most common sizes due to their ability to handle heavy freight loads. Lighter sizes like 115 lb are still used, while older branch lines may use 85 lb or 90 lb rail.

Q3: How do I identify a rail section without markings?
A: You can identify a rail section by measuring its height, base width, and head width using calipers or a tape measure. You then compare these measurements against a standard rail size chart to find the closest match.

Q4: What is the difference between 115 RE and 136 RE rail?
A: The 136 RE rail is heavier (136 lbs/yd) and physically larger (taller with a wider base and head) than the 115 RE rail (115 lbs/yd). The 136 RE is designed for heavier axle loads and higher traffic volumes.

Q5: Can different rail sizes be joined together?
A: Yes, different rail sizes can be joined using “compromise bars” or “compromise joints.” These are special joint bars designed to align the running surfaces and gauge sides of two rails with different heights and head widths.