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 CC-116
  
  **Hardware Type:**
            Barrier Terminals and Crash Cushions
                          **Code:**
            CC-116
                          **Date:**
            05/06/2011
                          **Testing Criteria:**
            NCHRP 350
                          **Manufacturer:**
            Eastern Federal Lands Highway Division
                          **Device Description:**
            Steel Backed Timber Guardrail Tangent End Terminal
                          **View PDF:**
            cc116.pdf (1.17 MB)
    
    Safety Eligibility Letter CC-116



			 

			**Download Version**PDF [1,216 KB]

			

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

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

			May 6, 2011

			In Reply Refer To: HSST/CC-116

			

		  Mr. Scott Whittemore

            	Highway Safety Engineer

                Federal Highway Administration
                
                Eastern Federal Lands Highway Division

                21400 Ridgetop Circle

                Sterling, VA  20166

           	Dear Mr. Whittemore:

            This letter is in response to your request for the Federal Highway Administration’s (FHWA) acceptance of a roadside safety device for use on the National Highway System (NHS).

		  Name of device:

					Steel Backed Timber Guardrail Tangent End TerminalType of device:

					Timber Guardrail Gating End TerminalTest Level:

					NCHRP 350 TL-2Testing  conducted by:

					National Crash Analysis CenterDate of  request:

					November 22, 2010Task Force 13 Designator:

					SED01You requested that we find this device acceptable for use on the NHS under the provisions of the National Cooperative Highway Research Program (NCHRP) Report 350 testing guidelines.

            **Requirements**Roadside safety devices should meet the guidelines contained in the NCHRP Report 350.  The FHWA memorandum “*ACTION*: Identifying Acceptable Highway Safety Features” of July 24, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

            **Description**The Steel Backed Timber (SBT) Guardrail Tangent End Terminal overall length is 12.42 meters 
(40 feet 9 inches).  It consists of nine (9) wood rail segments and nine (9) wood posts.  The rail segments’ cross-sectional area is 150 millimeters x 250 millimeters (6 inches x 10 inches), similar to the cross-section of the steel-backed timber SBT barrier rail segments.  The length of the first rail segment is 1.6 meters (5 feet 3 inches).  The last rail segment (number 9) is 1.75 meters (5 feet 9 inches) in length.  The remaining rails (numbers 2-8) are 1.676 meters (5 feet 6 inches) in length.  These rail segment lengths are about half the rail segment lengths of the SBT barrier and were selected such that the spacing between the posts is 1.22 meters (4 feet).  Both ends of the rail segments are cut at a 1:2 (26 degree) angle, with the exception of first rail segment, which has one end at 90 degree, and the last rail segment, which has one end cut at a 1:1 (45 degree) angle.  The first rail of the SBT guardrail is also cut at a 1:1 (45 degree) angle to fit the end of the terminal.

            The posts are 150 millimeters x 250 millimeters (6 inches x 10 inches) in cross-section and 2.1 meters (6 feet 11 inches) in length.  The post embedment in the ground is 1.43 meters (4 feet 8 inches), similar to the SBT barrier post embedment.  Holes are drilled in the posts at ground level.  The hole diameter for the first three posts is 115 millimeters (4.5 inches) and the hole diameter for the remaining six posts is 75 millimeters (3 inches).  Steel tubes encase the embedded portion of the wood posts to ensure consistent failure of the posts at ground level.  The tubes are 150 millimeters x 250 millimeters x 4.75 millimeters (6 inches x 10 inches x 3/16 inch) in cross-section and 1.422 millimeters (4 feet 8 inches) length.

The rail segments of the end-terminal are connected to the posts through steel splices and wood blockouts.  This setup is based on the original SBT barrier connection but was modified to allow for release of the rail segments from the posts in head on impacts and to absorb some the vehicle kinetic energy.  Details A, B, and C in Figure 8 show the end-terminal rail-to-post connections.  At each post, the ends of two adjacent rail segments are connected to the steel splice (splice plate?) through lag screws.  The lag screws are 16 millimeters (5/8 inch) in diameter and 100 millimeters (4 inches) in length.  Three lag screws are used to connect the splice to the rail segment that is closer to the start of the terminal while four lag screws are used for the adjacent rail segment.  With this configuration, the rail segment closer to the start of end-terminal will separate from post before the adjacent rail segment and allow for a more controlled deceleration of the vehicle during the head on impact.  The three lag screws are placed in 22 millimeter × 178 millimeter (7/8 inch × 7 inches) slotted holes and placed such that the screws pull out from the rail segments one at a time.  This design reduces the impact forces while maximizing the energy absorbed during the head on impact.  This setup was also configured such that the rail segments will not separate from the post during the redirection impacts.

The steel splices and wood blockouts are connected to the posts using 16 millimeter (5/8 inch) diameter bolts.  The bolts are 380 millimeters (15 inches) in length.  The steel splices are 150 millimeters × 750 millimeters × 10 millimeters (6 inches × 30 inches × 3/8 inch).  The wood blockouts are 300 millimeters × 225 millimeters × 100 millimeters (12 inches × 9 inches × 4 inches).  Both are of similar size to the original SBT barrier.

Drawings of the SBT Guardrail Tangent End Terminal are included as enclosures to this correspondence.

            **Crash Testing**The following methods used for analysis of the Backed Timber Guardrail Tangent End Terminal.

*Simulation* Computer simulations were performed to evaluate the end-terminal under the seven tests recommended for Test Level 2 (TL-2) impact condition. Results from these simulations are as follows.The simulation results showed that the final design meets all NCHRP Report 350 recommendations for gating end terminals under TL-2 impact conditions.  Based on these simulation results five tests were selected for testing.  These include tests 2-30, 2-31, 2-32, 2-34, and 2-35.  The other two tests, 2-33 & 2-39, were omitted based on the simulation results that showed that they meet requirements and are less critical than the remaining five. The test house therefore requests to waive the remaining two tests, 2-33 & 2-39.
	*Physical Crash Testing:* The NCHRP Report 350 outlines the criteria used to determine the crashworthiness of roadside features, including traffic barriers and their terminals.  The end terminal for the SBT guardrail was tested according to these requirements, but requested a waiver for two of the seven crash tests required for TL-2 based upon simulation and previous experience with gating terminals.  The test house has therefore conducted the following five out of seven crash tests:Test 2-30: An 820C small car impacting the end-terminal at an angle of 0 degrees and a speed of 70 km/hr (43.5 mi/hr).  The vehicle strikes the end-terminal head on with an offset of 1/4 the width of the vehicle.
    					Test 2-31: A 2000P pickup truck impacting the end-terminal at an angle of 0 degrees and a speed of 70 km/hr (43.5 mi/hr).  The vehicle strikes the end-terminal head on at the vehicle centerline.
    					Test 2-32: An 820C small car impacting the end-terminal at an angle of 15 degrees and a speed of 70 km/hr (43.5 mi/hr).  The vehicle strikes the end-terminal head on at the vehicle centerline.
    					Test 2-34: An 820C small car impacting the end-terminal at an angle of 15 degrees and a speed of 70 km/hr (43.5 mi/hr).  The vehicle strikes the end-terminal at the critical impact point (selected between posts 2 and 3 of the end-terminal).
    					Test 2-35: A 2000P pickup truck impacting the end-terminal at an angle of 20 degrees and a speed of 70 km/hr (43.5 mi/hr).  The vehicle strikes the end-terminal at the start of length of need point (selected at post 4 of the end-terminal).Crash test summaries of the above mentioned tests are provided as enclosures to this correspondence.

            **Findings**Based on the successful completion of the aforementioned simulation and NCHRP Report 350 tests, we agree that the SBT Guardrail Tangent End Terminal meets the evaluation criteria for NCHRP 350 on gating end terminals at TL-2 impact conditions.  In addition we also agree to the waiver of tests 2-33 & 2-39. Test 2-33 was a critical test specifically for turn-down terminals which are no longer recommended as an acceptable roadside safety installation.  In addition, test 2-39 is only specified if the terminal is positioned where being struck in the reverse direction at high speed is deemed to be likely.  This should be conveyed to the agency within the system specifications.

Therefore, the system described in the request above and detailed in the enclosed drawings is acceptable for use on roadways in Federal Lands jurisdiction only under the range of conditions tested, when such use is deemed acceptable by the engineer.

			Please note the following standard provisions that apply to the FHWA letters of acceptance:

			This acceptance provides a AASHTO/ARTBA/AGC Task Force 13 designator that should be used for the purpose of the creation of a new and/or the update of an existing Task Force 13 drawing.

	            This acceptance is limited to the crashworthiness characteristics of the devices 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 device 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 device 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 Manual for Assessing Safety Hardware.

                To prevent misunderstanding by others, this letter of acceptance is designated as number CC-116, 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 device for which the applicant is not the patent holder.  The acceptance letter is limited to the crashworthiness characteristics of the candidate device, 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 Michael S. Griffith */*

                        Michael S. GriffithDirector, Office of Safety TechnologiesOffice of Safety 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