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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter B-224

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U.S. Department of Transportation
Federal Highway Administration

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

December 23, 2011

In Reply Refer To:
HSST/B-224

Maura Sullivan
Mass DOT Highway Division
Accelerated Bridge Program
10 Park Plaza, Room 6500
Boston, MA  02116

Dear Ms. Sullivan:

This letter 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: T401 (Based on crash test of T4)
Type of system: Bridge Railing
Test Level: NCHRP Report 350 TL-2 or TL-3
Testing conducted by: Texas Transportation Institute (TTI)
Task Force 13 Designator: SBB09c
Date of request: September 8, 2011
Date initially acknowledged:

September 8, 2011

Date all information rec'd:

December 8, 2011

Decision:
The following device is eligible, with details provided below:

Based on a review of crash test results and an engineering analysis of the modifications made on the original railing, the device described herein meets the crashworthiness 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.

Description
This railing is 33-inches high with an 18-inch concrete parapet and a steel ellipse or rectangular tube 15 inches above the concrete. It has twin one-inch cut-plate posts spaced a maximum of 10 ft. apart. It features a bolt anchorage system for the steel rail posts that may be drilled and epoxy anchored allowing slip-forming of the concrete parapet. Its parapet is thicker than the T4 rail, from which its design is derived.

Requirements
Roadside safety devices should meet the guidelines contained in the NCHRP Report 350 or the American Association of State Highway and Transportation Officials' Manual for Assessing Safety Hardware (MASH).  The FHWA Memorandum "Identifying Acceptable Highway Safety Features" of July 25, 1997 provides further guidance on crash testing requirements of longitudinal barriers.

Crash Testing
The Texas Type T4 (A) Bridge Rail was tested to NCHRP Report 350 Test 3-11.  The report is summarized in the enclosed "Figure 11" from the TTI report.  The railing contained and redirected the vehicle.  The vehicle did not penetrate, underride, or override the installation. Maximum permanent deflection of the rail during the test was 5 mm. No detached elements, fragments, or other debris were present to penetrate the occupant compartment, or to show potential for penetrating the occupant compartment, nor to present undue hazard to others in the area.  Maximum occupant compartment deformation was 158 mm in the right floor pan to instrument panel location.  The vehicle remained upright during the collision and after loss of contact with the installation.  The vehicle trajectory may intrude into adjacent traffic lanes as it came to rest 6.1 m toward traffic lanes.  Longitudinal occupant impact velocity was 8.5 m/s, and the longitudinal ridedown acceleration was -9.7 g's.  Exit angle at loss of contact was 11.3 degrees which was 46 percent of the impact angle.

Damage to the Texas T4 (A) bridge rail was extensive.  The flange on the impact side of post 4 was marred and chipped as were the base plate and front bolts.  Both the top and bottom of the rail element were scarred to a distance of 190 mm from the impact face of the rail.  Structural cracks in the concrete portion of the rail occurred 400 mm from the center of post 4.  One extended 85 mm down the field side of the concrete parapet and another radiated from the right rear bolt and extended 95 mm down the rear.  A section of concrete (200 mm x 390 mm) broke out of the rear of the concrete beam deck under the bolt on the upstream field side and exposed the bolt.  Maximum dynamic deflection of the rail during the test was not attainable and maximum permanent deformation of the metal rail element was 5 mm.  Total length of contact of the vehicle with the bridge rail was 4.3 m.

Because of the extent of the damage to the railing, additional static and dynamic testing was done to the basic design of the T4.  The modified railing includes a thicker concrete parapet and drilled and epoxied bolts to anchor the rail to the top of the parapet.  The modified design was designated at the T401, the subject of this letter.

Findings
The Texas Type T4 (A) Bridge Rail successfully contained and redirected the vehicle which remained upright during and after the collision.  Improvements to the T4 to strengthen the concrete parapet and improve the constructability of the steel railing resulted in the T401 bridge railing. Because these modifications to the T4 do not adversely affect the crash test performance, the T401 system described in this letter and enclosures is considered eligible for reimbursement on Federal-aid highway projects. It should be installed under the range of conditions tested, when such use is acceptable to a highway agency.

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

 

Sincerely yours,

/* Signature of Michael S. Griffith */

Michael S. Griffith
Director, Office of Safety Technologies
Office of Safety

Enclosures

Page last modified on June 24, 2011.
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