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 SS-170
  
  **Hardware Type:**
            Sign Supports, Mailboxes, and Delineator Posts
                          **Code:**
            SS-170
                          **Date:**
            11/30/2012
                          **Testing Criteria:**
            NCHRP 350
                          **Manufacturer:**
            Minnesota Department of Transportation
                          **Device Description:**
            Minnesota Type "C" and "D" Braced Leg Sign Supports
Supports
                          **View PDF:**
            ss170.pdf (649.47 KB)
    
    Safety Eligibility Letter LS-74

			

						

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

**Download Version**PDF [1.05 MB]
 

SENT VIA ELECTRONIC MAIL
Subject:
ACTION:  Minnesota DOT Braced Leg
Sign Support Eligibility Letter SS-170
Date: November 30, 2012From:
    Michael S. Griffith

Director, Office of Safety Technologies 

Office of Safety
In Reply Refer To:
HSSTTo:William Stein, Safety Engineer
 
Minnesota DivisionThis memorandum is in response to your request for the Federal Highway Administration (FHWA) to review a roadside safety system for eligibility for reimbursement under the Federal-aid highway program.
Name of system:

 	 Minnesota Type "C" and "D" Braced Leg Sign SupportsType of system:

 	 U-Channel Sign Support SystemTest Level:

 	 NCHRP Report 350 Test Level 3Testing conducted by:

 	 Texas Transportation InstituteDate of request:
 	  November 23, 2010Date of completed package:
 	  September 26, 2012Initially acknowledged:
 	  December 13, 2010**Decision**
 The following device is eligible, with details provided below and in the drawings attached as an integral part of this memorandum:
Minnesota Type "C" and "D" Braced Leg U-Channel Sign Supports****Based on a review of crash test results submitted certifying the device described herein meets the crash test and evaluation criteria of the National Cooperative Highway Research Program (NCHRP) Report 350, the device is eligible for reimbursement under the Federal-aid highway program.  Eligibility for reimbursement under the Federal-aid highway program does not establish approval or endorsement by the FHWA for any particular purpose or use.

The FHWA, the Department of Transportation, and the United States Government do not endorse products or services and the issuance of a reimbursement eligibility letter is not an endorsement of any product or service.
**Test Descriptions**
 There were no tests performed pursuant to this request for product acceptance.
The FHWA, the Department of Transportation, and the United  States Government do not endorse products or services and the issuance of a  reimbursement eligibility letter is not an endorsement of any product or  service.
**Requirements**
  To be found eligible for Federal-aid funding, roadside  safety devices should meet the crash test and evaluation criteria contained in  the NCHRP Report 350 or the American Association of  State Highway and Transportation Officials’ Manual for Assessing Safety  Hardware (MASH).
**Description**
You requested that we review this system using two posts  within a seven-foot span under the provisions of the NCHRP Report 350.
The dual-post test installation consisted of an 8-foot  wide by 7-foot tall plywood sign panel mounted on two steel U-channel supports  spaced 39 inches apart. The supports were joined in a nested splice with two  stubs driven into "strong soil." The  stubs were 84 inches long with an embedment depth of 42 inches. The length of the structural splice between  the stub and the sign riser post was 30 inches, with the bottom of the riser  post 12 inches above ground level. Structural  splices for u-channel posts should be a minimum of 18-inches long with two  fasteners at each end of the splice piece.
The sign supports were braced with two additional supports  posts mounted diagonally at a slope of 1⁄212:1 to the rear of the installation. The braces were attached to the front supports  with A-frame brackets at the sign panel and anchored to two 48-inch stubs,  located 5 feet, 3 inches behind the front support stubs at 27-inch on center  spacing. The rear stubs were also driven  into the crushed limestone to a depth of 44 inches leaving 4 inches projecting  above ground level.
All posts and stubs were 2.5 pound-per-foot rerolled rail  steel u-channel posts. Stub-post connections and posts splices were joined with  5/16-inch by 1 1⁄2-inch alloy bolts, nuts, and washers. Both posts were struck  during the crash tests. A drawing of the  test installation is enclosed for reference.
Later crash testing of a three-post support used a similar  design with 3-pound-per-foot posts, but only two of the supports were  impacted. Additional posts may be used  to support wider signs, but no two posts may be closer than 7 feet.
**Crash Testing**
  Four tests were conducted under NCHRP Report 230 criteria  in 1988 and 1989. NCHRP Report 230 Tests  62 and 63 were conducted on both the Type "C" dual-post installation and the  Type "D" triple-post installation. The  dual-post 2.5-pound-per-foot installation yielded to the vehicle in both the  high- and low-speed tests and allowed it to proceed downrange. In the low-speed test of the triple-post  installation with two posts impacted, the two 3-pound-per-foot diagonal braces  that were impacted by the test vehicle yielded by breaking from their stubs,  but the two signposts subsequently brought the vehicle to a controlled stop. In the high-speed test both of the sign posts  and diagonal braces fractured, allowing the test vehicle to proceed through. The third post that was not impacted held the  sign in place. Copies of the Test Data  Summary Sheets are enclosed for reference. Type "C" and "D" refer to the number  of u-channel rails used as lateral braces on the back of "A Frame" signs. Type  "C" is a single brace while Type "D" is a dual brace as noted on page 2 of 3 of  the attached drawings.
Since NCHRP Report 230 tests 62 and 63 use the same 820-kg  test vehicle as specified in NCHRP Report 350 and the evaluation criteria are  comparable, these tests are considered compliant with NCHRP Report 350. The bottom of the signs that span two or  three posts should be a minimum of 7 feet above the ground. Supplemental signs  placed on just one of the posts may be mounted at 5 feet above the ground.
The results of this testing was known to the researchers  who conducted a series of sign support tests at the FHWA’s Federal Outdoor  Impact Laboratory in McLean, Virginia, from 1989 to 1991. When designing a braced-leg system of  u-channel posts they made two significant changes to the Minnesota design. The first was to use a breakaway splice for  the upright sign posts where the signpost overlapped the stub by six inches,  with the stub projecting no more than 4 inches above the ground. The second innovation was to use aluminum  fasteners to ease the separation of both the upright and diagonal posts from  their respective stubs. These changes  have the potential for improving the Minnesota braced leg design.
**Summary and Standard Provisions**
  Therefore, the system described and detailed in the  attached form is eligible for reimbursement and may be installed under the  range of conditions tested.
Please note the following standard provisions that apply to FHWA letters of acceptance:
This  finding of eligibility does not cover other structural features of the systems, nor conformity with the  Manual on Uniform Traffic Control Devices.
  Any  changes that may influence system conformance with NCHRP Report 350 criteria  will require a new reimbursement eligibility letter.
  Should  the FHWA discover that the qualification testing was flawed, that in-service  performance reveals safety problems, or that the system is significantly  different from the version that was crash tested, we reserve the right to  modify or revoke this letter.
  You are  expected to supply potential users with sufficient information on design and  installation requirements to ensure proper performance.
  You are  expected to certify to potential users that the hardware furnished has the same  chemistry, mechanical properties, and geometry as that submitted for review,  and that it will meet the crash test and evaluation criteria of the NCHRP  Report 350.
  To  prevent misunderstanding by others, this letter of eligibility is designated as  number SS-170 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  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 does not become  involved in issues concerning patent law. Patent issues, if any, are to be  resolved by the applicant.Attachment 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