# Truck Trailer Manufacturers Association — Hazardous Materials Safety Interpretation **Citation:** 98-0568 **Type / status:** guidance / guidance **Agency:** Pipeline and Hazardous Materials Safety Administration **Effective:** Not stated **Published:** 1993-06-23 98-0568 response to Truck Trailer Manufacturers Association concerning 178.345. ## Document text <<>> 1 of Transportation U.S. Department Washington, D C 400 Seventh Street, S.W. 20590 JUN 23 1993 ALice.s. Mr. Donald W. Vierimaa Vice President-Engineering Truck Trailer Manufacturers Association 1020 Princess Street Alexandria, VA 22314 Dear Mr. Vierimaa: This is in response to your letter concerning rollover protection requirements for a specification DOT 406 cargo tank. Specifically, you asked if a manufacturer, who uses two full length parallel overturn protection rails (inverted V rails), can design the rails so that each withstands one-half of the loads specified in 49 CFR 178.345-8(c)(1). The answer is no. In the case of inverted V rails that run along each side of the top of the cargo tank (not in the center), a rollover will cause a sudden impact of the ground with only one of the rails, then, if and when the tank rolls to 180 degrees, which seldom occurs, the second rail comes into : contact with the ground and experiences a different kind of loading. Then, if the tank continues to roll, the first railing will be suddenly released of all loading and the total load will shift entirely to the second rail. In such a rollover scenario, it is not reasonable for a designer to distribute the required loading between the two railings. However, a designer could provide for two inverted V railings to share the distribution of the transverse loading, by providing for transverse bracing to connect the two railings and to treat the entire design as a single device for the purpose of handling the transverse loading. Without transverse bracing, inverted V railings should be considered separate non-load-sharing devices. Other devices, such as "tombstones" are considered load sharing devices and are symetrically located along the centerline of the top of the cargo tank, so that in a normal overturn scenario, the devices strike the ground simultaneously and each device receives a sudden loading of similar magnitude. In such a case, it is reasonable to distribute the required design loading among all the devices. -- <<>> 2 If you need further assistance, please contact us. Sincerely, The #. Allan Thomas G. Allan Senior Transportation Regulations Specialist Office of Hazardous Materials Standards <<>> - i Flle: 178,345-8 SCi 333 ,310 Truck Trailer Manufacturers Association TANK CONFERENCE 1020. Princess Street, Alexandria, VA 22314 703-549-3010 Fax: 703-549-3014 Richard P. Bowling, President January 15, 1997 Edward T. Mazzullo Director Office of Hazardous Materials Standards Research & Special Programs Administration U.S. Department of Transportation 400 Seventh Street, S.W. Washington, D.C. 20590 Subject: Request for an Interpretation of Rollover Protection of 178.345-8(c)(1) Dear Mr. Mazzullo: Typically, two full length parallel overturn protection rails are installed on DOT 406 cargo tanks. It each of these overturn rails is designed to withstand one-half of the loads specified in 178.345-8(c)(1), will the pair of overturn rails comply with 178.345-8(c)(1)? Sincerely, Donald W. Vienned Donald W. Vierimaa DWV/mm Vice President-Engineering CC: Stephen Keppler Office of Motor Carriers, HSA-10 No, Each ra. / inus be - Federal Highway Administration Tank Conference Engineering Committee ts. in The •A. Pats ## Provenance - Official: Yes - Source: - Source ID: `phmsa` - SHA-256: `fb67b72f3821a6fefae9bc629361a8ca29930fc4b87b4c4eaf3f56f56fd13a4c` - Retrieved: 2026-08-20T00:59:31.977Z - Exported: 2026-08-22T10:06:43.486Z - Document slug: `phmsa-interpretation-98-0568` ### Source metadata ```json { "materialSubtype": "interpretation", "interpretationArea": "hazardous_materials", "representation": "full_text_from_official_pdf", "companies": [ "Truck Trailer Manufacturers Association" ], "individuals": [ "Mr. Donald W. 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