November 25, 2002
Refer to: HSA-10/SS-114
Mr. Darren Hesse
National Sales Manager
S-Square Tube Products
5495 East 69th Avenue
Commerce City, Colorado 80022
Dear Mr. Hesse:
Thank you for your July 12, 2002, letter to Mr. Nicholas Artimovich requesting Federal Highway Administration (FHWA) acceptance of your company=s NEX Tube as a breakaway component of a crashworthy mailbox support for use on the National Highway System (NHS). Accompanying your letter were photographs of your proposed mailbox mounting systems. You requested that we find the NEX Tube Mailbox Support System acceptable for use on the National Highway System under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features." On October 12, 2002, you provided additional information on a redesigned support for accommodating multiple mailboxes.
Pendulum and full-scale automobile testing of NEX Tube sign supports was completed in 1998, and was in compliance with the guidelines contained in the NCHRP Report 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. Requirements for breakaway supports are those in the American Association of State Highway and Transportation Officials' Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals. Our Acceptance Letter, SS-81, found the NEX Tube sign supports acceptable for use on the NHS.
The NEX Tube mailboxes use the same deformed cross-section 14 gage steel pipe, formed into what might be called a "question mark" shape. The base of the support is inserted into a ground socket and secured with a wedge. Drawings of the supports are enclosed for reference.
The testing of the NEX Tube sign supports showed that the socket and wedge arrangement was a successful breakaway design, with vehicle velocity changes well below the desirable limit of 3 m/sec for single supports and approximately 3 m/s for a dual post support. You asked that we compare your socket design to the V-Loc system, which has already been tested as a mailbox support. We concur with your assertion that the same technology will be effective as a single/double mailbox support. Therefore, the NEX Tube sign support will be acceptable for use as a single/double mailbox support using the socket and wedge design as shown in the enclosed drawings.
You also asked that we accept the NEX tube for use with multiple mailboxes using the "nverted coat hanger" arrangement. When the V-Loc system was tested with a multiple mailbox support (using 14 gage steel pipe in an "inverted coat hanger" arrangement) the occupant impact speeds were almost at the limit of acceptability. Because your design did not replicate the basic "closed loop" shape of the V-loc system, we were not as certain that five-box support using the NEX tube would meet the occupant impact velocity requirements. You have since redesigned your multiple mailbox support to replicate the "inverted coat hanger" arrangement, which we expect will perform in an acceptable manner.
The single/double mailbox support and the "inverted coat hanger" multiple mailbox support described above and shown in the enclosed drawings for reference are acceptable for use as Test Level 3 devices on the NHS under the range of conditions tested, when proposed by a State. The single box supports are considered crashworthy for conventional rural mailboxes weighing up to 5 pounds. The multiple box supports are considered crashworthy when boxes weighing up to 3.5 pounds each, are used.
Please note the following standard provisions that apply to FHWA letters of acceptance:
Carol H. Jacoby, P.E.
Director,Office of Safety Design