Federal Highway Administration
400 Seventh St., S.W.
Washington, D.C. 20590
January 23, 2007
Refer to: HSSD/SS-144
Mr. Bryan Reeves
ARC Technologies, LLC
966 Liledoun Road
Taylorsville, NC 28681
Dear Mr. Reeves:
Thank you for your mail correspondence of August 18, 2006, requesting the Federal Highway Administration (FHWA) acceptance of your company's simulated stone mailbox columns for use on the National Highway System (NHS). Accompanying your letter was a report on testing of this roadside hardware conducted by the Texas Transportation Institute, test videos and digital photographs. You requested that we find it acceptable for use on the NHS under the provisions of the National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features."
Mailbox supports should meet the guidelines contained in the NCHRP Report 350, "Recommended Procedures for the Safety Performance Evaluation of Highway Features". The FHWA memorandum "ACTION: Identifying Acceptable Highway Safety Features" of July 25, 1997, provides further guidance on crash testing of breakaway supports.
The ARC simulated stone mailbox column for use on the NHS is fabricated as a hollow, one-piece rotational casting. The hardened shell or wall of the column has a thickness that ranges from 0.19 in. (4.8 mm) to 0.38 in. (9.7 mm) and is comprised of two layers or coats. The first coat or face mix, which has a thickness ranging from 0.09 in. (2.3 mm) to 0.19 in. (4.8 mm), consists of gypsum, sand, liquid and dry resin, hardener, accelerator, and pigment. The second coat or back-up mix is comprised of a two-component polyurethane and has a thickness ranging from 0.09 in. (2.3 mm) to 0.19 in. (4.8 mm). The exterior surface of the column is molded to resemble stone masonry construction.
The column measures 20 in. x 20 in. x 62 in. tall (508 mm x 508 mm x 1575 mm). The upper cap of the mailbox column measures 24 in. x 24 in. (610 mm x 610 mm). A U.S. Postmaster approved T2 mailbox measuring 21 in. long x 8 in. wide x 10.5 in. high (533 mm x 203 mm x 267 mm) is cast into the column at a height of 40 in. (1016 mm) to the bottom of the mailbox.
A 6 in. (152 mm) diameter x 16.5 in. (419 mm) long plastic newspaper tube is also cast into the mailbox column at a height of 30 in. (762 mm) to the bottom of the tube. The upper two thirds of the hollow simulated stone column is backfilled with two-part Instapak FlowRiteTM foam that has a molded density of 1.0-1.4 lb/ft3 (16.0-22.4 kg/m3).
Test article installation
In tests, the ARC simulated stone mailbox column was installed on precast concrete foundation pad measuring 24 in. x 24 in. x 2.5 in. thick (610 mm x 610 mm x 64 mm) and weighing 64 lb (29 kg) placed level to and flush with the surrounding ground. The pad was secured in place by driving two 0.38 in. (9.7 mm) diameter x 18 in. (457 mm) long anchoring spikes into the ground through precast holes. The bottom shell of the mailbox column was secured to the top surface of the concrete foundation pad through liberal application of Liquid NailTM adhesive. The pattern use for the adhesive included a line around the perimeter of the mailbox column and several lines extending radially outward from the center to the outer edges of the column.
Full-scale automobile testing which included the NCHRP report 350 Test 3-60 (low-speed test) and the NCHRP Report 350 Test 3-61 (high speed test) was conducted on your company’s mailbox column. The complete device as tested is shown in the enclosed drawing. The NCHRP Report 350 test 3-60 involved an 820 kg passenger car (820C) impacting the mailbox column head-on with the left quarter point of the vehicle aligned with the centerline of the mailbox column at a nominal impact speed and angle of 35 km/h and 0 degrees, respectively. The NCHRP Report 350 test 3-61 involved an 820 kg passenger car (820C) impacting the mailbox column head-on with the right quarter point of the vehicle aligned with the centerline of the mailbox column at a nominal impact speed and angle of 100 km/h and 0 degrees, respectively.
In the low-speed test, the simulated stone mailbox column yielded to the vehicle by breaking apart at the base. The largest fragment, which weighed 75 lb (34.0 kg), rode up the windshield (which shattered) and over the top of the vehicle. The fragment did not penetrate or show potential for penetrating the occupant compartment, nor to present hazard to others in the area. No occupant compartment deformation occurred. The vehicle remained upright during and after the impact. Occupant risk factors were within the preferred limits. The vehicle did not intrude into adjacent traffic lanes, as it traveled through the test site and came to rest 103 ft (31.4 m) behind the point of impact. The summary of test results is enclosed.
In the high-speed test, the simulated stone mailbox column yielded to the vehicle by breaking apart at the base. The largest piece weighed 53 lb (24.0 kg), rode up the windshield (which shattered) and over the top of the vehicle. The fragment did not penetrate or show potential for penetrating the occupant compartment, nor to present hazard to others in the area. Occupant compartment deformation was 3.5 in. (91 mm) in the roof area over the right front seat, which is less than the maximum acceptable roof crush criterion for breakaway support structures of 5 in. (127 mm) as established by the FHWA. The vehicle remained upright during and after
the collision event. Occupant risk factors were within the preferred limits. The vehicle did not intrude into adjacent traffic lanes, as it traveled through the test site and came to rest 370 ft (113 m) behind the point of impact and 11.8 ft (3.6 m) to the left of centerline. The summary of test results is enclosed.
The results of testing met the FHWA requirements and, therefore, the ARC simulated stone mailbox column described above and shown in the enclosed drawings for reference is acceptable for use as the NCHRP Report 350 Test Level 3 device on the NHS, when selected by the contracting authority, subject to the provisions of Title 23, Code of Federal Regulations, Section 635.411 as they pertain to proprietary products.
Please note the following standard provisions that apply to the FHWA letters of acceptance:
/original signed by /
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety
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