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                Safety Eligibility Letter B-175
  
  **Hardware Type:**
            Longitudinal Barriers and Bridge Rails
                          **Code:**
            B-175
                          **Date:**
            06/28/2008
                          **Testing Criteria:**
            NCHRP 350
                          **Manufacturer:**
            MWRSF
                          **Device Description:**
            MGS with round DougFir, PonderosaPine, SYPine
                          **View PDF:**
            b175.pdf (1.73 MB)
    
    Safety Eligibility Letter B-175

			 
			**Download Version**PDF [1.26 MB]
			
			DOT logoU.S. Department of Transportation**Federal Highway Administration**
			1200 New Jersey Ave. S.E.Washington, D.C. 20590
			June 25, 2008
			In Reply Refer To: HSSD/B-175
			
			Ronald K. Faller, Ph.D., P.E.
				Research Assistant Professor
				University of Nebraska Lincoln
				527 Nebraska Hall
				P.O. Box 880529
			Lincoln, NE 68588-0529
			Dear Dr. Faller:
			This letter is in response to your request for Federal  Highway Administration (FHWA) acceptance of a roadside safety system for use on  the National Highway System (NHS).
			Name of  system: Midwest Guardrail System (MGS) with round posts:Douglas Fir, Ponderosa Pine, Southern Yellow  Pine
				Type of  system: 31-inch high W-Beam guardrail system
				Test Level:  NCHRP Report 350 Test Level 3
				Testing  conducted by: Midwest Roadside Safety Facility
				Date of  request: September 26, 2007You requested that we find this system acceptable for use on  the NHS under the provisions of National Cooperative Highway Research Program  (NCHRP) Report 350 “Recommended Procedures for the Safety Performance  Evaluation of Highway Features.”
			**Requirements**Roadside safety systems should meet the  guidelines contained in the NCHRP Report 350, "Recommended Procedures for  the Safety Performance Evaluation of Highway Features". FHWA Memorandum “ACTION:  Identifying Acceptable Highway Safety Features” of July 25, 1997 provides  further guidance on crash testing requirements of longitudinal barriers.
			**Description** The MGS was first recognized in the FHWA  Acceptance Letter B-133 dated March 1, 2005.  In that letter it was described as follows:
			The MGS barrier consists of standard  12-gauge W-beam sections installed with the top of the rail set at a nominal  height of 787 mm (31 inches). It is  mounted on standard W152 x 13.4 steel posts that are 1829-mm (6-feet) long and  set on 1905-mm (75-inch) centers. To  obtain the additional rail height, each post is raised approximately 100 cm (4  inches), resulting in slightly less embedment than the posts in a  standard W-beam installation. The rail  is offset from these posts with 152-mm wide x 305-mm deep x  356-mm long (6-inch x 12-inch x 14-inch) wood offset blocks. Finally, the rail splices are located at  mid-span between adjacent posts rather than at each post as in a traditional  W-beam installation.
			Your **present request** is to allow the use of round wood posts of Douglas  Fir (DF), Ponderosa Pine (PP), and Southern Yellow Pine (SYP) based on research  conducted by the Forest Products Laboratory (FPL) and full-scale crash testing  you conducted. The FPL research  developed the following grading specifications for the three varieties of wood  posts.
			Species
                DF
                PP
                SYPMaximum Knot Diameter
                2    in
                4    in
                2.5    inMinimum Ring Density
                6    rings/in
                6    rings/in
                4    rings/inNominal Post Diameter*
                7.25    in
                8.00    in
                7.50    inPost Diameter Range*
                7.00    to 8.00 in
                7.75 to 8.75 in
                7.25    to 8.25 in*Post diameter at the ground line.
			**Crash  Testing** The MGS barrier was subjected to two  NCHRP Report 350 3-11 crash tests, MGSDF-1 using Douglas Fir posts, and MGSPP-1  using Ponderosa Pine posts. Because of  prior testing of the MGS using SYP posts, tests on other w-beam barrier systems  using round SYP posts, and the initial MGS test using the 820C vehicle  (reported in B-133 noted above) only the two 3-11 tests were deemed necessary. Test Data Summary Sheets for the two tests are  enclosed for reference. The occupant  risk criteria were met for both impacts as was the post-impact trajectory, with  no potential noted for spearing or deformation of the passenger compartment.
			For the test on the Douglas Fir system  (test no. MGSDF-1), the W-beam rail located upstream of the impact region had  fallen to the ground after the test. For  the test on the Ponderosa Pine system (test no. MGSPP-1), a smaller portion of  the W-beam rail located upstream of the impact region had fallen to the ground  after the test. The maximum dynamic  deflection in test MGSDF-1 was 60 inches, and in test  MGSPP-1 was 38 inches. For comparison,  the maximum dynamic deflection in test NPG-4 using steel posts, reported in  B-133, was 43 inches.
			**Findings** The MGS system described above using DF, PP, and SYP posts  and detailed in the enclosed drawings is acceptable for use on the NHS under  the range of conditions tested, when such use is acceptable to the highway  agency.
			Please note the following standard  provisions that apply to the FHWA letters of acceptance:
			This acceptance is limited to the  crashworthiness characteristics of the systems and does not cover their  structural features, nor conformity with the Manual on Uniform Traffic Control  Devices.
			  Any changes that may adversely  influence the crashworthiness of the system will require a new acceptance  letter.
			  Should the FHWA discover that the  qualification testing was flawed, that in-service performance reveals  unacceptable safety problems, or that the system being marketed is  significantly different from the version that was crash tested, we reserve the  right to modify or revoke our acceptance.
			  You will be expected to supply  potential users with sufficient information on design and installation  requirements to ensure proper performance.
			  You will be expected to certify to  potential users that the hardware furnished has essentially the same chemistry,  mechanical properties, and geometry as that submitted for acceptance, and that  it will meet the crashworthiness requirements of the FHWA and the NCHRP Report  350.
			  To prevent misunderstanding by others,  this letter of acceptance is designated as number B-175 and shall not be  reproduced except in full. This letter  and the test documentation upon which it is based are public information. All such letters and documentation may be  reviewed at our office upon request.
			  This acceptance  letter shall not be construed as authorization or consent by the FHWA to use,  manufacture, or sell any patented system for which the applicant is not the  patent holder. The acceptance letter is  limited to the crashworthiness characteristics of the candidate system, and the  FHWA is neither prepared nor required to become involved in issues concerning  patent law. Patent issues, if any, are  to be resolved by the applicant.Sincerely yours,
						Signature of David A. Nicol
						David A. Nicol, P.E.Director, Office of Safety DesignOffice of SafetyEnclosures U.S. DEPARTMENT OF TRANSPORTATION

**Federal Highway Administration**

1200 NEW JERSEY AVENUE, SE

WASHINGTON, DC 20590

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