Tank Car Class and Specification Markings

The tank car DOT number designates the exact specification to which it was designed. DOT class stencils are located on the side of the tank car at the BL and AR locations just above the tank test date and below the product stencil, if one is applied.

This is a DOT 111A100 W. This stencil indicates the following:

DOT - Designates the Department of Transportation which is the authorizing agency.

111 - Designates a specific design. There are over ninety designs.

A - Equipped with top and bottom shelf couplers.

100 - Is the Hydrostatic and / or maximum design pressure of this unit.

W - Designates this tank is made of a welded construction.
The picture below shows some of the markings found in this area, but there are also other designations which vary depending on the type of tank car.
Additional tank car specifications which could be found in this area are shown on the tank car below. The specifications that are present vary depending on the type of tank car. A detailed description of each item follows the picture.
Authorizing Agency
Tank car classes and specification numbers begin with a three letter prefix which represents the authorizing agency as follows:

  • DOT - Department of Transportation
  • AAR - Association of American Railroads
  • ICC - Interstate Commerce Commission (regulatory
    authority assumed by DOT in 1965)
  • CTC - Canadian Transport Commission

AAR tank cars differ from DOT tank cars by as little as the use of a fitting that does not meet DOT requirements but is necessary for handling the particular commodity being transported.
Tank Car Class
The DOT has specified over ninety different classes of tank cars.
Letter Indication (Number Significance)
A - equipped with top and bottom shelf couplers
S - equipped with tank head puncture resistance in addition to top and bottom shelf couplers

J - equipped with jacketed thermal protection in addition to tank head puncture resistance and top and bottom shelf couplers

T - equipped with spray-on thermal protection in addition to tank head puncture resistance and top and bottom shelf couplers
Tank Test Pressure
When present, this stencil item represents the tank test pressure in pounds per square inch.
Letter Type of the Material Used in Construction
(No Letter) - Carbon steel
AL - Aluminum (found in Classes 103, 105, 109, and 111)
N - Nickel (found in Class 103 only)
D - Stainless steel (found in Class 103 only)
Weld Construction Type
W - Fusion welding

F - Forge welding
Fittings/Material/Lining (If applicable)
Linings can be made of lead, rubber, or other elastomeric material.
Safety Valves

Safety valve stencils are also found here:

    SAFETY VALVE 75 PSI
    TESTED 1998 UTC-85 DUE 2008


The UTC 85 - Union Tank Car Shop # 85 performed the tank and safety valve test. They must be a DOT approved shop to hydrostatically test, repair and test safety valves as well as repair tank cars. The safety valve was tested for 75 PSI in 1998 and will be due on or before December 31, 2008.

Most tank cars only have one safety valve.

Tank Test

The tank was tested for 100 PSI in 1998 and will be due on or before December 31, 2008:

    TANK 100 PSI
    TESTED 1998 UTC-85 DUE 2008


All testing on tank cars (except those in Chlorine service) must be completed by the last day of the year due, regardless of the month tested. Chlorine tank cars must be tested on or before the last day of the month (originally) tested, in the year due.

The certified testing papers must be kept in the main tank car file. They are usually kept by the Corporate Logistics Department. Even though the tank car stencil indicates the test has been performed, without the certified test papers the tank car would not have been inspected as required by the DOT.

Important: File records are the only true indication a test was completed. Stencil records that do not match file records will be discarded.

The tank car shown to the right has two safety valves (as compared to AIDX 2000). They are identified by the letters "A" and "B". They both must be properly inspected and documented on or before the inspection due date.