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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter B-198

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U.S. Department of Transportation
Federal Highway Administration

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

January 12, 2010

In Reply Refer To:
HSSD/B-198

Mr. Ronald K. Faller, Ph.D
Research Assistant Professor
Midwest Roadside Safety Facility
University of Nebraska-Lincoln
527 Nebraska Hall
Lincoln, NE 68588-0529

Dear Dr. Faller:

You requested that we formally find this device acceptable for use on the National Highway System (NHS) under the provisions of American Association of State Highway and Transportation Officials, Manual for Assessing Safety Hardware (MASH). This letter is a response to your request for the Federal Highway Administration (FHWA) acceptance of a roadside safety device for use on the NHS.

Name of device: West Virginia TL-1 Timber Curb-Type Bridge Barrier
Type of device: Permanent Timber Barrier Bridge Railing
Test Level: AASHTO Manual for Assessing Safety Hardware (MASH) TL-1
Testing conducted by: Midwest Roadside Safety Facility (MwRSF)
Date of request: September 13, 2009
Date of completed package: September 13, 2009
Task Force 13 Designator: SBD05a

Requirements
Roadside safety devices should meet the guidelines contained in the MASH.

Description
For this project, the research objective was to adapt an existing, crashworthy, Test Level 1 (TL-1) curb-type bridge barrier for use on transverse, timber, nail-laminated bridge decks supported by steel wide-flange beams. The barrier system was redesigned to meet the TL-1 impact safety standards set forth by MASH. The existing MwRSF curb-type timber bridge barrier system was successfully crash tested to the TL-1 safety performance criteria as per NCHRP Report 350. This timber bridge barrier system served as the basis for the new West Virginia TL-1 Timber Curb-Type Bridge Barrier design. However, the railing for this project was required to meet the TL-1 safety performance criteria provided in MASH. Therefore, modifications were made to the previous system in order to accommodate the increased impact severity and increased vehicle height resulting from the 2270P vehicle as per current MASH guidelines. These changes are described as follows.

The test installation consisted of three major sub-systems: (1) a 120-ft (36.6-m) long, nail-laminated, timber bridge deck placed on wide-flange, steel girders; (2) a curb-type, timber bridge railing system; and (3) a 35-ft (10.7-m) long, sloped, safety treatment located on the upstream end of the bridge barrier. The total length of the test installation was 155 ft (47.2 m).

The bridge barrier system consisted of three major structural components: (1) a longitudinal, glulam timber rail; (2) steel H-splice plates; and (3) post assemblies consisting of sawn lumber scupper blocks.

The glulam timber rail consisted of 19.9-ft (6.08-m) long, glulam rail segments with a 6-3/4 in. x 12 3/8 in. (171 mm x 314 mm) cross section, as shown in Figure 36. The glulam rails were manufactured from Combination No. 48 Southern Yellow Pine and were treated with pentachlorophenol in heavy oil to a minimum net retention of 0.60 lbs/ft3 (9.61 kg/m3) conforming to the American Wood Preserver’s Association (AWPA) use category UC4A [8]. The ends of each rail segment were narrowed to a width of 11 5/8 in. (295 mm) in order to accept the steel H-splice plates and allow the outer plate surface to be flush with the gross rail section.

The steel H-Splice plates were fabricated from ASTM A656 Grade 50 Type 7 material. The two side plates were 34 3/4 in. long by 6 3/4 in. wide by 3/8 in. thick (883 mm x 171 mm x 9.5 mm) with twelve 1 1/8-in. (29-mm) diameter holes. For the H-splice, the center connecting plate was installed orthogonal to the outer two plates and measured 11 5/8 in. long by 6 3/4 in. wide by 3/8 in. thick (295 mm x 171 mm x 9.5 mm). The H-splice plates connected adjacent glulam rail segments end to end using six 1-in. (25.4-mm) diameter by 14-in. (356-mm) long, ASTM A307 galvanized dome-head bolts in each rail end.

The bridge rail post assemblies consisted of two timber scupper blocks stacked on top of each other. Each scupper block was fabricated from Grade No. 1 Southern Yellow Pine sawn lumber and measured 23 in. long by 9 1/2 in. wide, and 7 1/2 in. tall (584 mm x 241 mm x 191mm). Four 13/16-in. (21-mm) diameter bolt holes were drilled in the scuppers at 5-in. (127-mm) spacing intervals.

The West Virginia TL-1 Timber Curb-Type Bridge Barrier drawings for the construction of the test installation are included with this correspondence.

Findings
We concur with your request that the West Virginia TL-1 Timber Curb-Type Bridge Barrier that has been successfully crash tested to AASHTO MASH TL-1 conditions will be considered acceptable for use on the NHS, assuming all other factors such as timber specifications and component details are identical to the tested version. For further information on the crash test, the Test Data Summary Sheet is included with this correspondence.

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

 

Sincerely yours,

Signature of George E. Rice, Jr.

for David A. Nicol, P.E.
Director, Office of Safety Design
Office of Safety

Enclosures

Page last modified on June 24, 2011.
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