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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #21-0039

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: Tank Car Safety

Individual Name: Kenneth Dorsey

Location State: DC Country: US

View the Interpretation Document

Response text:

July 19, 2021

Mr. Kenneth Dorsey
Executive Director of Tank Car Safety
425 3rd St SW
Washington, DC  20024

Reference No. 21-0039

Dear Mr. Dorsey:

This is in response to your April 13, 2021, letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to identification plates on rail tank cars. Your questions are paraphrased and answered below.

Q1: You seek clarification as to which modifications to a rail tank car would require the use of a variable identification plate as described in § 179.24(a)(3) of the HMR. Specifically, you ask whether the term "modification" as referenced in § 179.24(a)(3) is intended to have the identical meaning as the term "modification" as defined in § 180.503.

A1: The answer is no. Section 180.503 defines a "modification" as "any change to a tank car that affects the certificate of construction prescribed in § 179.5, including an alteration prescribed in § 179.6, or conversion." Section 179.24(a)(3) states that when a modification to the tank changes any of the information shown in paragraph (a)(2) of § 179.24, the car owner or the tank car facility making the modification must install an additional variable identification plate on the tank in accordance with § 179.24(a)(1) and stamp, emboss, or otherwise mark the information identified in § 179.24(a)(3)(i)-(ii). Therefore, it is the opinion of this Office that a modification as described in § 180.503 would not always necessitate a modification as described in § 179.24(a)(3).

Q2: You seek confirmation that the tank car's identification plate required in § 179.24(a)(2) is used to indicate the configuration of the tank car at the time it entered service and that the additional variable identification plate required in § 179.24(a)(3) is used to record changes to that tank car's original configuration.

A2: Your understanding is correct.

Finally, your letter notes that § 179.24(a)(3) establishes that an additional variable identification plate must show—among other requirements—all of the items in § 179.24(a)(2) that were modified. In addition, § 179.24(a)(2)(iv) requires the original identification plate include the "specification to which the tank was built from line 7 of Association of American Railroads (AAR) Form 4-2." However, you note that a modification that would trigger a change to a tank car's Department of Transportation (DOT) specification occurs through AAR-established processes by way of change to the stencil specification in line 8 of the AAR Form 4-2, not line 7 as referenced in § 179.24(a)(2)(iv). You add that the information required in § 179.24(a)(2)(iv) will never change on an AAR Form 4-2. PHMSA appreciates AAR bringing this information to our attention and will take your comments into consideration.

I hope this information is helpful. Please contact us if we can be of further assistance.


T. Glenn Foster
Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division

179.5, 179.6, 179.24, 179.24(a)(1), 179.24(a)(2), 179.24(a)(2)(iv), 179.24(a)(3), 179.24(a)(3)(i)-(ii), 180.503

Regulation Sections

Section Subject
179.24 Stamping
179.5 Certificate of construction
179.6 Repairs and alterations
180.503 Definitions