Federal Highway Administration
400 Seventh St., S.W.
Washington, D.C. 20590
March 22, 2005
Refer to: HSA-10/WZ-200
Mr. Marc Christensen
Off the Wall Products, LLC
P.O. Box 1461
Salt Lake City, Utah 84110
Dear Mr. Christensen:
Thank you for your letter of January 28, 2005, requesting Federal Highway Administration (FHWA) acceptance of your company's MB-42 x 45 high-density polyethylene (HDPE) units as crashworthy traffic control devices for use in work zones on the National Highway System (NHS). Accompanying your letter were drawings of both the original and newly designed units and material specifications for them. You requested that we find the new devices acceptable by virtue of their similarity to the original units you had tested under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features." You asked that they be accepted as a Longitudinal Channelizing Barricade at test level 1 (TL-1) when linked together and as TL-3 Manual Uniform Traffic Control Devices Type II Barricades when they stand alone. You also followed up with additional information on March 10, 2005.
The FHWA guidance on crash testing of work zone traffic control devices is contained in two memoranda. The first, dated July 25, 1997, titled "INFORMATION: Identifying Acceptable Highway Safety Features," established four categories of work zone devices: Category I devices are those lightweight devices which are to be self-certified by the vendor, Category II devices are other lightweight devices which need individual crash testing but with reduced instrumentation, Category III devices are barriers and other fixed or heavy devices also needing crash testing with normal instrumentation, and Category IV devices are trailer mounted lighted signs, arrow panels, etc. for which crash testing requirements have not yet been established. The second guidance memorandum was issued on August 28, 1998, and is titled "INFORMATION: Crash Tested Work Zone Traffic Control Devices." This later memorandum lists devices that are acceptable under Categories I, II, and III.
A brief description of the devices follows:
The original MB-48 x 40 (initially called MB-2) was a rotation molded hollow linear low-density polyethylene (LLDP) plastic barricade section which can accept water ballast. Each high impact, UV-resistant polyethylene section is 48 inches tall and 40 inches long. Each section is 23.5 inches wide at the base, tapering on one side to a top width of 6 inches. The wall thickness is 0.20 inches, and one section weighs 50 pounds empty.
This unit was tested and accepted as stand-alone Type II barricade units (FHWA acceptance letter WZ-8 dated February 5, 1999, TL-3). During the crash test, the plastic lens from the warning light broke loose and impacted the windshield, causing minor cracking.
Linked together, the units were also tested as a Longitudinal Channelizing Barricade (FHWA acceptance letter WZ-135, dated March 27, 2003, TL-1.) The test vehicles penetrated the system, as expected, but the vehicle trajectories were satisfactory and the occupant risk criteria were within acceptable limits. No parts of the LCB contacted the windshield.
The new MB-42 x 45 HDPE units are blow molded with HDPE and measure 40 inches long and 48 inches tall. Each section is 22.5 inches wide at the base, tapering on one side to a top width of 5 inches. The wall thickness is 0.156 inches and a single unit weighs 35 pounds when empty. The new units are 6 inches lower, 5 inches longer, and 15 pounds lighter than the tested units. The maximum water ballast that they can hold is 721 pounds, or 200 pounds less than the crash tested version. Because the tensile strength of the HDPE is significantly greater than that of the low density material, the wall thickness can be reduced using the HDPE and still maintain the strength of the units similar to the LLDPE crash-tested units.
Request and Findings
You requested acceptance of the new MB-42x45 HDPE units as Test Level 3 stand-alone Type II barricades and as a TL-1 Longitudinal Channelizing Barricade just as the original MB-48 x 40 was tested. We concur in your request that the crash tests originally conducted, and documented in the FHWA acceptance letters WZ-8 and WZ-135 using the MB-48 x 40 are adequate to document satisfactory performance of the new MB-42x45 as Test Level 3 stand-alone Type II barricades and as a TL-1 Longitudinal Channelizing Barricade, respectively. As a stand-alone Type II barricade there is no greater potential for windshield contact at TL-3, and as an Longitudinal Channelizing Barricade (LCB) we see no greater likelihood of adverse vehicle trajectory or potential for greater occupant risk at TL-1.
The change in fabrication from a roto-molded product using low-density polyethylene (MB-48 x 40) to a blow-molded product using high-density polyethylene (MB-42 x 45) may affect the performance of the devices. The thinner HDPE walls of the new units are roughly 20 percent stronger than the thicker LLDPE walls in the tested units. You have arranged to have a TL-3 test (NCHRP Report 350 Test 3-10) conducted on the MD-42 x 45 HDPE LCB to assess the high-speed performance of the new units. Assuming the test is successful, you asked that the FHWA consider this test as sufficient to judge the TL-3 performance of the original MB-48 x 40 also. We agree in principal to this request, but reserve final judgment pending our analysis of the crash documentation to verify that performance will be comparable.
Based on the analysis above we concur that the new MB-42 x 45 HDPE units will be acceptable as TL-3 stand-alone Type II barricades and as a TL-1 LCB for use on the NHS under the range of condition that the MB-48 x 40 was tested, when proposed by a State.
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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