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                Safety Eligibility Letter B-211A
  
  **Hardware Type:**
            Longitudinal Barriers and Bridge Rails
                          **Code:**
            B-211A
                          **Date:**
            06/10/2011
                          **Testing Criteria:**
            NCHRP 350
                          **Manufacturer:**
            MWRSF
                          **Device Description:**
            Midwest Guardrail System placed adjacent to a 2H:1V fill slope
                          **View PDF:**
            b211a.pdf (565.74 KB)
    
    Safety Eligibility Letter B-211A
			

						
**Download Version**PDF [139 KB]

			DOT logoU.S. Department of Transportation**Federal Highway Administration**

			1200 New Jersey Ave. S.E.Washington, D.C. 20590

			June 10, 2011

			In Reply Refer To: HSSD/B-211A

			

			Mr.  Dean L. Sicking, Ph.D., P.E.
			  Director,  Midwest Roadside Safety Facility
			  University  of Nebraska - Lincoln
			  P.O.  Box 880601
		    Lincoln,  NE  68588-0601
			Dear Mr. Sicking:

          This  letter is in response to Messrs. Robert Bielenberg and Ronald Faller request  for the Federal Highway Administration (FHWA) acceptance of a wood post  alternative to the steel post Midwest Guardrail System (MGS) installed adjacent  to a 2H:1V fill slope.
Name of  system:

               	  Midwest Guardrail System placed adjacent to a  2H:1V fill slopeType of system:

               	  Wood Post and W-beam roadside barrierTest Level:

               	  NCHRP Report 350 Test Level 3Testing conducted by:

               	  Midwest Roadside Safety FacilityDate of request:

               	  December 21, 2010Date initially acknowledged:
           	    December 23, 2010Task Force 13 Designator:
           	    SGR38You  requested that we find a wood post MGS barrier design to be an acceptable  alternative to the recently-accepted steel post design when installed at the  hinge point of a 2H:1V fill slope.  You  further requested that the wood post option also be accepted for use on the  National Highway System (NHS) as a TL-3 barrier under the provisions of the  National Cooperative Highway Research Program (NCHRP) Report 350.
**Requirements**
  Roadside  safety devices should meet the guidelines contained in NCHRP Report 350 when  tested prior to January 1, 2011, and the guidelines in American Association of  State Highway Transportation Official's Manual for Assessing Safety Hardware after  that date.  The FHWA memorandum "ACTION:  Identifying Acceptable Highway Safety Features" of July 24, 1997, provides further  guidance on crash testing requirements of longitudinal barriers and crash  cushions.
**Decision**
  The  following barrier design was found acceptable, with details provided below:
MGS adjacent to a 2H:1V fill slope with 7.5 feet (2.29  meters) long wood posts**Description**
  The MGS system has been successfully  crash-tested when installed at the hinge point of a 2H:1V fill slope with 9 feet  (2.74 meters) long W6 × 9 (W152 × 13.4) steel posts at a standard spacing of 75  inches (1902 millimeters) on centers.  This  design was accepted by the FHWA for use on the NHS via acceptance letter B-211.   Subsequently, the Midwest  Roadside Safety Facility was requested  to develop a 6 inches × 8 inches (152 millimeters × 203 millimeters) wood post  alternative to the steel post design.   This alternative design used 7.5 feet (2.29 meters) long wood posts on  75 inches (1902 millimeters) centers to support the W-beam rail element at the  MGS height of 31 inches (78.7 millimeters).
**Crash  Testing**
  Surrogate testing of single posts was  performed using a rigid frame bogie weighing approximately 1800 pounds (820  kilograms) and accelerated to 15 mph (24 km/h).   Since the objective of the test program was to determine a wood post  size that corresponded closely to the 9 feet (2.74 meters) steel posts  previously crash-tested, two of the 7 bogie tests used the steel posts set at  the 2H:1V slope breakpoint.  The  remaining five bogie test used 6 inches × 8 inches (152 millimeters × 203  millimeters) standard wood posts with lengths of 7.5 feet (2.29 meters) and 8  feet (2.44 meters) and with embedment depths from 58 to 64 inches (1,473 to 
  1,626 millimeters).  All posts were installed with the center of  each post at the slope breakpoint, one foot (30.5 millimeters) away from the  road side of the 3 feet (914 millimeters) diameter drilled shafts that were  then backfilled with compacted 8 inches (203 millimeters) lifts.
**Findings**
  A  summary of all bogie testing results is shown in the enclosure to this  letter.  Review of the data from all  seven impact tests found that the 7.5 feet (2.29 meters) long, 6 inches × 8 inches 
(152  millimeters × 203 millimeters) SYP wood posts provided the best alternative to  the 9 feet (2.74 meters) long, W6 × 9 (W152 × 13.4) steel posts.  Three tests of 8 feet (2.44 meters) long, 
6 inches  × 8 inches (152 millimeters × 203 millimeters) SYP wood posts resulted in post  fracture due to the post-soil forces exceeding the capacity of the wood  post.  The wood fracture prevented  effective rotation of the post in the soil and resulted in insufficient energy  absorption during the impact.  Thus, the  8 feet (2.44 meters) long, wood posts were deemed unsuitable for the MGS when  installed adjacent to a 2H:1V fill slope. In contrast, the 7.5 feet (2.29  meters) long, 6 inches × 8 inches (152 millimeters × 203 millimeters) SYP wood  posts correlated reasonably well with the data obtained from the 9 feet (2.74  meters) long, W6 × 9 (W152 × 13.4) steel post tests.  The 7.5 feet (2.29 meters) long posts did not  fracture during impact and rotated through the soil.  The average peak force for the two 7.5 feet  (2.29 meters) long, wood post tests was only 5.7 percent greater than the  average peak force of the two W6 × 9 (W152 × 13.4) steel post tests.  Similarly, the average total energy of the  two 7.5 feet (2.29 meters) long, wood post tests was only 
6.5  percent greater than the average total energy of the two W6 × 9 (W152 × 13.4)  steel post tests.  The average force  levels for the 7.5 feet (2.29 meters) long, wood post tests were 23 percent  greater through 15 inches (381 millimeters) of deflection than the values  obtained from the steel post testing.  Thus,  the two 7.5 feet (2.29 meters) long, wood posts compared very well with the  steel posts in terms of peak force and total energy absorbed, while being  slightly higher in terms of average force.   It is not believed that the reasonably small differences observed  between the 7.5 feet (2.29 meters) long, wood post and the 9 feet (2.74 meters)  long, steel post would have any adverse effects on the performance of the MGS  system.
In  subsequent e-mail correspondence, Mr. Bielenberg noted that a standard W-beam  barrier was successfully tested at the breakpoint of a 2H:1V slope using 7 feet  (2.13 meters) wood posts at 1/2 the standard post spacing.  We believe that the use of slightly longer  posts, combined with the additional height of the W-beam and the use of the  deeper offset blocks in the MGS system, would result in crash performance  similar to that seen in the successfully tested steel post design.
Based  on the above considerations, the FHWA agrees that the 7.5 feet (2.29 meters)  long, 
  6 inches  × 8 inches (152-millimeter × 203-millimeter) SYP wood post provides a suitable  alternative to the 9 feet (2.74 meters) long, W6 × 9 (W152 × 13.4) steel post.****
Please  note the following standard provisions that generally apply to all the FHWA  letters of acceptance:
This  acceptance letter provides an AASHTO/ARTBA/AGC Task Force 13 designator that  should be used for the purpose of creating a new or revised Task Force 13  drawing.
  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 (when applicable).
  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 NCHRP Report 350.
  To  prevent misunderstanding by others, this letter of acceptance is designated as  number B-211A 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.
  The  MGS barrier design is not a patented product, nor is it considered proprietary.  However, if any proprietary devices are specified by a highway agency for use  on Federal-aid projects, except exempt, non-NHS projects, (a) they must be  supplied through competitive bidding with equally suitable unpatented items;  (b) the highway agency must certify that they are essential for synchronization  with the existing highway facilities or that  no equally suitable alternative exists; or (c) they must be used for research  or for a distinctive type of construction on relatively short sections of road  for experimental purposes.  Our  regulations concerning proprietary products are contained in Title 23, Code of  Federal Regulations, Section 635.411.
  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 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 Michael S. Griffith */*

						Michael S. Griffith
Director, Office of Safety  Technologies
Office of SafetyEnclosures U.S. DEPARTMENT OF TRANSPORTATION

**Federal Highway Administration**

1200 NEW JERSEY AVENUE, SE

WASHINGTON, DC 20590

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