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                Safety Eligibility Letter B-56B
  
  **Hardware Type:**
            Longitudinal Barriers and Bridge Rails
                          **Code:**
            B-56B
                          **Date:**
            09/05/2003
                          **Testing Criteria:**
            NCHRP 350
                          **Manufacturer:**
            Structures of Ironwood
                          **Device Description:**
            Design alternative: rectangular timber rail
                          **View PDF:**
            b56b.pdf (50.67 KB)
    
    
United States Department of Transportation - Federal Highway Administration
  August 15, 2003HSA-10/B56B
Mr. David Hubbell
    Structures of Ironwood
    P.O. Box 600
    Saranac Lake, New York 12983
  Dear Mr. Hubbell:
  In your July 17 letter to Mr. Richard Powers of my staff, you requested acceptance 
    of a modification to the design of your Ironwood barrier.  The original design 
    was approved for use on the National Highway System in Mr. Dwight A. Horne's 
    June 18, 1999 letter to you.
  You have requested the use of a 203-mm deep by 178-mm wide timber rail element 
    as an alternative to the originally tested 203-mm diameter round timber rail.  
    This alternative design serves to increase the effective height of the barrier 
    by changing the traffic face of the rail (i.e., the 203-mm dimension) from 
    a curved surface to a vertical surface. Even with the change in rail shape, 
    the Ironwood barrier should be installed at a minimum height of 660 
    mm to the top of the rail as tested, but a mounting height up to 710 mm is 
    suggested to increase the performance limits of the barrier.  Since Ironwood 
    is a weak-post design, vehicular snagging on the posts is not likely at the 
    higher rail height and a higher rail is likely to perform better under varied 
    crash scenarios.
  I find your request to use rectangular timber rails as an alternative to 
    round rails on the TL-3 Ironwood barrier to be acceptable.  The same timber 
    species/specifications noted for the round rail will apply to the alternative 
    design.
  
  Sincerely yours,
        (original signed by John Baxter)
        John Baxter
          Director, Office of Safety Design
          Office of Safety
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