AAR Car Type Codes Explained & Resources

The Association of American Railroads (AAR) car type codes system is a comprehensive classification used to categorize the various types of railcars in use today.

Understanding these codes is crucial for professionals in the railway industry, as they provide essential information about the characteristics and capabilities of each car type.

In this detailed guide, we will explore the nuances of AAR car type codes, providing insights into their structure, significance, and how they are used in the industry.

Understanding the AAR Car Type Codes

Code Structure:

  • First Letter: The first letter of the AAR code identifies the major category of the railcar.
  • Following Numbers: The next three numbers specify more detailed characteristics, such as dimension, roof type, door type, capacity (in gallons or cubic feet), load limit, floor type, coupler type, tank type, unloading type, etc. These numeric categories vary for each major railcar category​​.

Example of Code Breakdown:

  1. Covered Hopper Example (C112): In the code ‘C112’, ‘C’ stands for a covered hopper. The numbers break down as follows:
    • 1st number: Type of unloading mechanism (e.g., gravity unloading)
    • 2nd number: Type of roof
    • 3rd number: Capacity in cubic feet (e.g., 3,000 to 4,000 cubic feet)​​.
AAR Car Type Codes Explained & Resources

Major Categories of Railcars

  • Equipped Box Cars (A): These are box cars with specific equipment for cargo securing.
  • Unequipped Box Cars (B): Standard box cars without additional equipment.
  • Covered Hopper Cars (C): Used for transporting dry bulk commodities.
  • Locomotive (D): The engine or the power car of the train.
  • Equipped Gondola (E): Gondolas with special equipment for cargo.
  • Flat Cars (F): Open cars used for large or awkwardly shaped cargo.
  • Unequipped Gondola (G): Basic gondola cars without special equipment.
  • Unequipped Hopper (H): Basic hopper cars for bulk commodities.
  • Gondola Car (J): Typically used for transporting heavy bulk commodities.
  • Equipped Hopper Cars (K): Hoppers equipped with specific features for certain types of cargo.
  • Special Type Cars (L): Cars designed for specific or unusual types of cargo.
  • M-O-W, Scale, Passenger, Caboose, and End-of-train Information Systems (M): Miscellaneous category including maintenance cars and passenger cars.
  • Conventional Intermodal Cars (P): Standard intermodal cars for containers.
  • Lighter Weight, Low-Profile Intermodal Cars (Q): Specially designed for efficient intermodal transport.
  • Refrigerator Cars (R): Cars equipped with refrigeration for perishable goods.
  • Stack Car (S): Designed for carrying containers stacked on top of each other.
  • Tank Cars (T): Used for transporting liquids and gases.
  • Containers (U): Standardized containers for various types of cargo.
  • Vehicular Flat Cars (V): Flat cars designed specifically for transporting vehicles.
  • Trailers (Z): Used for transporting standard road trailers on rail​​.

Resources for Deciphering Numeric Codes

The numeric part of the AAR code varies depending on the major car category. To understand these codes in detail, certain resources are necessary:

  • The Official Railway Register: Often referred to as the “big yellow book,” this resource provides comprehensive information on all numeric codes for each major car type. It is available for purchase and is considered the ultimate resource for AAR car type codes.
  • Rail Fan Sites: Some websites offer explanations of these numeric codes. However, their information might be outdated, and accuracy is not guaranteed.
  • BNSF Railway Page: BNSF Railway provides an online platform where you can enter any railcar number to view its characteristics along with the AAR Car Type Code​​.

UMLER Car Type Codes

UMLER® (Universal Machine Language Equipment Register) is a critical data source for over two million pieces of North American rail, steamship, and highway equipment. It serves as a key system for equipment management and reporting, offering secure access to users such as railroads, equipment owners, shippers, and various industry stakeholders.

The UMLER system details internal and external dimensions, capacities, weight information, and other specific characteristics of freight cars, as well as intermodal trailers and containers​​.

AAR Mechanical Designation Codes

The AAR Mechanical Designation Codes are an integral part of the rail industry’s classification system, developed by the Association of American Railroads (AAR). These codes provide a standardized method for identifying the mechanical characteristics and specifications of railroad cars.

Understanding these codes is crucial for various stakeholders in the rail industry, including operators, manufacturers, and maintenance personnel, as they ensure uniformity and clarity in the identification and management of railcar types.

Overview of AAR Mechanical Designation Codes

  1. Purpose and Functionality:
    • Standardization: The AAR Mechanical Designation Codes standardize the way railcars are identified based on their physical and mechanical characteristics. This uniformity is essential for efficient operation, management, and regulation of railcar fleets.
    • Categorization: These codes categorize railcars into groups based on their design, purpose, and capacity, aiding in logistics, maintenance, and regulatory compliance.
  2. Code Structure:
    • Format: The codes typically consist of a combination of letters and numbers, each signifying specific attributes of a railcar.
    • Mechanical Features: The codes can include information on the type of car, the specific design features (such as the type of braking system, loading mechanism, or structural features), and the intended cargo or service type.

Detailed Breakdown of the Codes

  1. Car Type Codes:
    • These designate the general category of the railcar (e.g., tank car, flatcar, hopper car).
  2. Load Capacity:
    • Codes often include information on the load capacity of the car, vital for determining appropriate usage and compliance with safety standards.
  3. Specific Design Features:
    • Details about the car’s design, such as the type of couplers, trucks (wheel assemblies), and braking systems.

Application in the Rail Industry

  1. Railcar Management and Logistics:
    • The codes are used to ensure that the right type of car is used for specific cargoes, especially when it comes to hazardous materials or specialized cargo.
  2. Maintenance and Manufacturing:
    • Manufacturers and maintenance crews rely on these codes to ascertain the specifications for building and servicing railcars.
  3. Safety and Regulatory Compliance:
    • Understanding these codes is essential for compliance with safety regulations, as different types of railcars have different safety requirements and standards.

Challenges and Evolutions

  • Keeping Up-to-Date: The rail industry is continually evolving, with new technologies and regulations emerging. Keeping the AAR Mechanical Designation Codes up-to-date with these changes is crucial.
  • Training and Knowledge Dissemination: Ensuring that industry personnel are trained in understanding and applying these codes is vital for safety and efficiency.

The listed items represent a selection of AAR Mechanical Designations that are suitable for application on the HO Scale Middle Division in the 1950s era.

Freight Cars

FB – Flat Car, bulkhead
FC – Flat Car, trailer service
FD – Flat Car, depressed center
FM – Flat Car, general service
FW – Flat Car, well hole
GA – Gondola, drop bottom, cross doors dump between the rails
GB – Gondola, solid floor, may have drop ends for mill service
GD – Gondola, solid floor, side doors
GH – Gondola, drop bottom, longitudinal doors dump outside the rails
GS – Gondola, drop bottom, longitudinal doors dump outside the rails
GT – Gondola, high side rotary dump
HM – Hopper, 2-bay
HT – Hopper, 3- & 4-bay
HK – Hopper, longitudinal doors dump outside the rails
LG – Gondola or Flat Car, equipped to carry containers
LO – Hopper, covered
NE – Caboose, eight wheel
NM – Caboose, four wheel
RA – Refrigerator, brine cooled
RAM – Refrigerator, brine cooled, beef rails
RB – Refrigerator, ice cooled, no ice bunkers
RCD – Refrigerator, solid carbon dioxide cooled
RP, RPA, RPB – Refrigerator, mechanically cooled, powered by car axle
RS – Refrigerator, ice cooled
RSM – Refrigerator, ice cooled, beef rails
SA – Stock Car, single deck
SC – Stock Car, convertible single or double deck
SF – Stock Car, double deck
SH – Horse Car
SM – Stock Car
SP – Stock Car, poultry
TA – Tank Car, specialized
TG – Tank Car, glass lined
TL – Tank Car, lined other than glass
TM, TMU – Tank Car, specialized
TP – Tank Car, specialized
TR – Tank Car, specialized
VA – Ventilated Box Car, fruits or vegetables
VM – Ventilated Box Car, fruits or vegetables, partially insulated
VS – Ventilated Box Car, fruits or vegetables, insulated
XAF – Box Car, automobile or furniture
XAP – Box Car, automobile parts with racks
XAR – Box Car, automobile with loading racks, end door
XF – Box Car, furniture
XI – Box Car, insulated
XM – Box Car, general service
XME – Box Car, merchandise with racks
XMP – Box Car, specially equipped racks not otherwise specified
XMR – Box Car, automobile with loading racks, end door
XT – Box Car, metal lined or containing one or more tanks

Passenger Cars

BE – Baggage Express
BEM – Baggage Express Messenger
BH – Horse Express
BM – Milk Car, non-refrigerated
BMR – Mike Car, refrigerated
BP – Refrigerator Express
BR – Refrigerator Express, ice cooled
BRS – Refrigerator Express, brine cooled
BX – Box Express
CA – Combination baggage/passenger
CAD – Combination baggage/passenger w/food service
CO – Combined passenger/baggage/mail
CS – Combination baggage/smoking car
CSA – Combination baggage/dormitory/kitchen
CSB – Combination baggage/dormitory
CSP – Combination mail or baggage/dormitory/passenger
DA – Dining Car
DC – Cafe Car
DCL – Lunch Counter Lounge
DD – Diner Dormitory
DE – Dining Car, less kitchen
DG – Grill Room Car
DK – Dormitory-Kitchen Car
DKP – Kitchen Car
DL – Buffet-Lounge Car
DLC – Lunch Counter Car
DO – Cafe Observation Car
DP – Dining and Parlor Car
DPA – Diner-Lounge Car (pantry instead of kitchen)
EB – Electric Baggage Car
EC – Electric Combination Car
ED – Rail Motor Car
EG – Motor Propelled Car
EM – Electric Mail Car
EP – Electric Passenger Car
ET – Electric Passenger Trailer Car
IA – Instruction Car
MA – Postal Car
MB – Baggage and Mail Car
MBE – Combination Mail-Baggage-Express
MBD – Combination Mail-Baggage-Dormitory Car
MD – Comination Mail-Dormitory Car
MR – Postal Storage Car
MS – Mail and Smoker Car
PAS – Coach-Sleeping Car
PB – Coach or Chair Car
PBC – Parlor-Coach
PBO – Coach-Observation Car
PC – Passenger, Parlor or Chair Car
PD – Tavern Car
PL – Lounge Car
PO – Observation Car
PS – Sleeping Car
PSA – Dormitory Car
PT – Tourist Car
PV – Private Car, including business cars

M-o-W Cars

MWB – Ballast Car
MWC – Caboose or Tool Car
MWD – Dump Car
MWE – Ballast Spreader and Trimmer
MWF – Flat Car
MWG – Section Gang or Track Inspection Car
MWH – Hand Car
MWJ – Ballast Unloader
MWK – Snow Removing Car
MWL – Hand Car
MWM – Store-Supply Car
MWP – Pile Driver
MWS – Steam Shovel
MWT – Tool & Block Car
MWU – Wrecking Derrick
MWV – Wrecking Derrick, flat car mounted
MWW – Wrecking Derrick
MWX – Boarding Car, boarding, sleeping, cooking, etc.

Rail Car Identification Chart

A Rail Car Identification Chart is a crucial tool in the railway industry, designed to aid in the identification and classification of various types of railcars. These charts are essential for professionals in the sector, including railroad employees, shippers, manufacturers, and logistics experts, providing a systematic approach to recognizing and understanding the wide variety of railcars in use.

Understanding Rail Car Identification Charts

  1. Purpose and Use:
    • Identification: The primary purpose of a rail car identification chart is to help users correctly identify different types of railcars. This is particularly important for logistics planning, maintenance, and safety management.
    • Standardization: The chart ensures standardization in the naming and categorization of railcars, which is crucial for efficient communication and operations within the industry.
  2. Key Components of the Chart:
    • Visual Representations: Typically, the chart includes illustrations or photographs of different railcar types. These visuals are accompanied by labels and annotations.
    • Car Type Codes: It incorporates various coding systems, such as the AAR (Association of American Railroads) car type codes, which provide a standardized language for identifying car types.
    • Specifications and Features: The chart details the unique features and specifications of each car type, including dimensions, capacity, and intended use.

Types of Railcars in the Identification Chart

  1. Boxcars: Enclosed cars used for a variety of goods, particularly those needing protection from the elements.
  2. Flatcars: Open deck cars used for heavy or oversized loads.
  3. Gondolas: Open-topped cars with sides and ends, used for bulk commodities.
  4. Hoppers: Cars with bottom-discharge for transporting bulk commodities.
  5. Tank Cars: Cylindrical cars designed for liquid or gas transport.
  6. Refrigerator Cars: Insulated and temperature-controlled for perishable goods.
  7. Intermodal Cars: For transporting shipping containers or trailers.
  8. Specialty Cars: Designed for specific cargoes like automobiles, livestock, etc.

Railcar Identification in Practice

  • For Railroads and Shippers: The chart assists in planning and allocating the right type of car for specific cargo. It ensures that cargoes are transported in the most efficient, safe, and regulation-compliant manner.
  • For Manufacturers and Maintenance Crews: Understanding different car types is crucial in designing, manufacturing, and maintaining these vehicles. The chart provides a reference for specific design features and requirements.
  • For Regulatory Compliance: Regulatory agencies use these charts to ensure that the correct types of railcars are used for specific kinds of cargo, especially hazardous materials.


The AAR car type codes system is a vital tool in the rail industry, enabling efficient and accurate classification of railcars. Understanding these codes is essential for professionals in the field, as they provide critical information regarding the specifications and capabilities of different railcar types.

With the help of the resources mentioned, one can decode and comprehend the complexities of these codes, leading to more informed decisions and better management in rail transportation.