USA Banner
  U.S. flag
              An official website of the United States government Here's how you knowOfficial US Government Icon
              **Official websites use .gov**A **.gov** website belongs to an official government organization in the United States.
            Secure Site Icon
              **Secure .gov websites use HTTPS**
                  A **lock** ( A locked padlock ) or **https://** means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites. 
 U.S. Department of Transportation Icon United States Department of Transportation
 Search DOT
            Search
                    About FHWAFHWA Organization
                Headquarters Offices
                Field Offices
                Strategic Plan
                Business Opportunities
                Staff Directories
                Careers
                Highway History
                Contact UsProgramsAcquisition Management
                Civil Rights
                Federal Lands Highway
                Infrastructure
                Innovative Program Delivery
                Operations
                Planning, Environment, and Realty
                Policy
                Research, Development, and Technology
                Safety
                Browse by TopicsResourcesCore Highway Topics
                Federal Aid Essentials
                Automation
                Complete Streets
                Laws and Regulations
                Policy & Guidance Center
                Section 508
                Publications and Statistics
                Professional Development
                National Highway Institute
                Resource Center
                Accessibility Resource Library
                FHWA Research LibraryNewsroomPress Releases
                Speeches & Testimony
                Photos
                Videos
                Media ContactsMenu FHWA Highway Safety Programs Home
                        Safety
                        Roadway Departure Safety
                        Reduce Crash Severity
                        Hardware Eligibility Letters


            
            In This Section
        Roadway Departure Safety
                Strategic Approach
                                Strategic Plan
                Crash Emphasis Brochures
                Focused Approach
                Noteworthy Practices
                Partner Resources
                Keep Vehicles on the Road
                                Pavement Friction
                Horizontal Curve Safety
                Rumble Strips and Rumble Stripes
                Nighttime Visibility
                Provide for a Safe Recovery
                                SafetyEdge
                Clear Zones
                Reduce Crash Severity
                                Overview
                Hardware Eligibility Letters
                Focus on Reducing Rural Roadway Departures (FoRRRwD)
                                Overview
                All Public Roads
                Proven Countermeasures
                Systemic Approach
                Safety Action Plans
                FoRRRwD Resources
                
                Safety Eligibility Letter B-64B
  
  **Hardware Type:**
            Longitudinal Barriers and Bridge Rails
                          **Code:**
            B-64B
                          **Date:**
            03/10/2004
                          **Testing Criteria:**
            NCHRP 350
                                  **Device Description:**
            guardrail posts in rock or mowing strips
                          **View PDF:**
            b64b.pdf (109.01 KB)
    
    
  Skip to contentUnited States Department of Transportation - Federal Highway AdministrationMemorandum

Subject:
INFORMATION:  W-Beam Guardrail Installations in Rock and in
	Mowing Strips
Date:
March 10, 2004From:
***/Original Signed by/***
From:	John R. Baxter, P.E.
	Director, Office of Safety Design 
	Office of Safety
In Reply Refer to:
HSA-10/B64-BTo:
Safety Field
	Federal Lands Highway Division EngineersStrong-post (both wood and steel posts) w-beam guardrail is designed to absorb some crash energy through post rotation in the soil prior to post failure.  Restraining these posts by setting them in narrow holes drilled into solid rock, by setting them in concrete, or by placing a “mowing strip” around the posts can lead to early post failure, placing more load on the rail element itself and possibly leading to rail rupture and subsequent penetration by an impacting vehicle.  Such behavior has been modeled using finite element analysis and verified in a limited number of full-scale tests.  Two papers were presented this year at the TRB meeting in Washington, D.C. that addressed concerns related to w-beam guardrail performance when its support posts were restrained from deflecting upon impact.
The first of these was the MwRSF report entitled “Development of Guidelines for Placement of Guardrail Posts in Rock” by Rohde and Herr.  The authors' final recommendations for guardrail placement in rock are summarized in Enclosure 1.  Simply stated, posts in solid rock should be set near the roadside edge of 530-mm to 580-mm diameter shafts drilled 610-mm (24-inches) deep, and backfilled with a compressible material (ASTM C33 coarse aggregate, size no. 57) so the post can rotate back approximately 380 mm (15 inches) at the ground line upon impact.  For locations where the solid rock is below the surface, the size and depth of the drilled shaft will vary as noted as the enclosure, depending on the depth of soil above the solid rock.
The second paper was the TTI report entitled “Evaluation of Guardrail Systems Performance When Encased in Pavement Mowing Strips” by Seckinger, Abu-Odeh, Bligh, and Roschke.  The authors' summary recommendations for the design of mowing strips around w-beam barrier are shown in Enclosure 2.  As noted, a minimum “leave-out” area in the mow strip that will allow at least 180-mm (7 inches) of post deflection at the ground line is recommended.  This area is then backfilled with a low-strength concrete mix.
Concrete with a 28-day compressive strength of .85 Mpa (120 psi) was used in the crash tests, but any suitable backfill material having equal or lesser compressive strength may be used.
The AASHTO Task Force for Roadside Safety will review these recommendations and is likely to incorporate them in whole or in part into the next edition of the Roadside Design Guide.  A secondary benefit of the recommended installation practices is increased ease of removal and replacement of any posts damaged in a crash.  State DOT's should review their standard plans and specifications for strong post w-beam in light of these research findings and consider revisions where deemed appropriate.  Electronic copies of both reports are included on the 2004 TRB CD that was given to all registered attendees.
Attachments
FHWASafety 
    Home | FHWA Home 
    | Feedback
  United States Department of Transportation 
    - Federal Highway Administration U.S. DEPARTMENT OF TRANSPORTATION

**Federal Highway Administration**

1200 NEW JERSEY AVENUE, SE

WASHINGTON, DC 20590

202-366-4000Subscribe to email updates
                    About
  

        
              About FHWA
                Careers
                Org Chart
                Staff Directories
                Work with UsPrograms
  

        
              Acquisition Management
                Civil Rights
                Federal Lands Highway
                Infrastructure
                Innovative Program Delivery
                Operations
                Planning, Environment, and Realty
                Policy
                Research, Development, and Technology
                SafetyPolicies, Rights, Legal
  

        
              About DOT
                Accessibility
                Budget and Performance
                Civil Rights
                FOIA
                Information Quality
                No FEAR Act
                Office of Inspector General
                Privacy Policy
                USA.gov
                Web Policies and Notices
                Web StandardsNews & Events
  

        
              Newsroom
                Press Releases
                Speeches & Testimony
                Media Contacts
                Connect with Us