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Railroad Car Plate Clearances

This page was last updated on March 28, 2026.

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AAR Plate Classification

In railroad terminology, Plate B, Plate C, Plate E and Plate F refer to standardized loading gauges, or clearance diagrams defined by the Association of American Railroads (AAR). These diagrams define the maximum height and width a freight car can have to safely clear bridges, tunnels, poles, signals, and trackside structures across the North American rail network. These standards are maintained by the Association of American Railroads.

Regardless of Plate designation, the width of a rail car is often reduced for very long cars to account for overhang or "swingout" when the car rounds a curve.

Civil engineers use these plate designations to determine how much clearance is needed when building new bridges or overhead power lines.

AAR Plate Classifications Compared

Plate Designation	Max Height	Max Width	Common Usage
Plate B	15' 1"	10' 8"	Universal standard; fits almost all routes. Adopted in 1948, revised in 1963.
Plate C	15' 6"	10' 8"	Standard for modern boxcars and hoppers. Adopted in 1963.
Plate E	15' 9"	10' 8"	High-cube boxcars. Adopted in 1963.
Plate F	17' 0"	10' 8"	Tall equipment; restricted to high-clearance routes. Adopted in 1974.
Plate H	20' 2"	10' 8"	Double-stack containers. Adopted in 1991.
Plate H (Lineside)	23' 0"	12' 0"	Current standard for lineside clearance

The 13-Degree Curve Rule

Each of the AAR Plate diagrams is based on the car's ability to negotiate a 13-degree curve (roughly a 441-foot radius). The truck-center limit is mathematically derived so that:

Center-of-Car Swing: The amount the middle of the car shifts toward the inside of the curve.

End-of-Car Swing: The amount the couplers and corners shift toward the outside of the curve.

For each truck-center limit these two "swing-out" values are roughly equal. If the truck-center is exceeded without narrowing the car, the center-of-car swing would exceed the clearance diagram on the inside of the curve.

Plate B: The Post War Standard

If a railcar fits within the Plate B diagram, it is generally cleared for unrestricted interchange across the entire North American network. Plate B ensures that a car sent from Mexico to Canada won't get stuck in a tunnel in Pennsylvania.

Even though Plate B is "safe" for most routes, some very old branch lines or specific urban tunnels may still have restrictions.

While there are larger plates (like Plate C or the massive Plate H for double-stack containers), Plate B is the lowest common denominator. If a car meets Plate B specs, it can go almost anywhere.

From The AAR Clearances Guide Book (Plate B):

Plate C: The Industry Workhorse

Plate C is the most prevalent clearance profile on modern rail networks. It allows for a maximum height of 15 feet 6 inches. Most standard freight equipment is built to this specification because it permits higher capacity than the older Plate B while remaining compatible with 95 percent of the North American rail system.

From the AAR Clearances Guide Book (Plate C):

Plate F: High-Cube Capacity

AAR Plate F was adopted by the Association of American Railroads in 1974.

(AAR Plate E was adopted at the same time, but with lower maximum height.)

The 1974 adoption of Plate F was a pivotal moment in rail history as the industry moved toward high-capacity equipment to compete with long-haul trucking. This era saw the rise of:

• High-Cube Boxcars: Often marked with a white "excess height" band at the top.
• Triple-Deck Auto Racks: Which required the extra vertical room Plate F provided.

Plate F is designated for "High-Cube" equipment, reaching a height of 17 feet 0 inches. These cars are primarily used for high-volume, low-density freight such as automotive parts or large appliances.

This clearance plate was introduced to accommodate the increasing height of freight equipment, specifically high-cube boxcars and specialized oversized loads. Plate F allows a limit of 17 feet 0 inches, while Plate E (adopted at the same time) set a maximum height of 15 feet 9 inches.

Plate F limits truck centers to 46 feet 3 inches or less (same as Plate C and Plate E). At truck centers of 46 feet 3", the swingout at ends of car do not exceed the swingout at center of car on a 13-degree curve.

When Plate F truck centers exceed 46 feet 3", car width is reduced to allow for the increased swingout at center and/or ends of car on a 13-degree curve so that the width of car does project excessively beyond the center of track.

If the truck centers are increased beyond 46 feet 3 inches to as much as 55 feet 1 inches (a common length for specialized equipment), the maximum allowable width typically drops to approximately 10 feet 2 inches.

Unlike Plates B and C, which allow for "unrestricted interchange," Plate F equipment is considered "limited interchange" because at that time many older routes, particularly in the Northeast, did not originally have the vertical clearance to accommodate 17-foot tall cars.

Plate H: The Current Standard

The AAR Plate H clearance diagram was adopted in September 1991 to accommodate the increasing use of double-stack container cars in North American interchange service.

Unlike the earlier Plates B and C, which were the industry standards for decades, Plate H was specifically designed for "high" equipment, primarily double-stack cars carrying two 9' 6" containers.

The Plate H diagram allows for a significantly taller profile than standard freight cars, though the width remains consistent with the standard 10' 8" maximum (subject to reduction for long truck centers).

Plate H is the primary standard for double-stack intermodal equipment. Because of its height, Plate H cars are restricted to specific "High-Wide" routes where tunnels, bridges, and signals have been undercut or raised to provide the necessary 20' 2" clearance.

The dimensions are based on a car with truck centers of 46' 3" and its overhang on the standard 13-degree curve.

The current standard for new lineside infrastructure construction on the North American rail network is not less than Plate H, allowing clearance of 23 feet maximum height and 12 feet maximum width, with top-of-rail to top-of-equipment clearance for 25KV electrification.

The big clearance problem is not tunnels, like everyone thinks. It's highway overpasses. Thousands and thousands of highway overpasses. For existing construction, tunnel floors can be lowered, but raising highway overpasses gets expensive very quickly. The added cost of potentially interfering with existing sub-grade water tables, grade-crossings, utility lines, pipelines, and drainage brings with it enormous costs.

Stenciling and Identification

To prevent accidents, freight cars are stenciled with their plate designation—typically a letter inside a small square. Dispatchers and yard crews use these markings to ensure that over-height cars are not routed through restricted trackage.

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