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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter B-212

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U.S. Department of Transportation
Federal Highway Administration

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

June 10, 2011

In Reply Refer To:
HSST/B-212

Ms. Karla A. Lechtenberg, MSME, EIT
Research Associate Engineer
Midwest Roadside Safety Facility
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853

Dear Ms. Lechtenberg:

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

Name of system: Midwest Guardrail System
Type of system: Steel Post and W-beam roadside barrier
Test Level: AASHTO Manual for Assessing Safety Hardware Test Level 3
Testing conducted by: Midwest Roadside Safety Facility
Date of request: December 18, 2010
Date initially acknowledged: December 18, 2010
Task Force 13 Designator: SGR20 a-b

You requested that we find this system acceptable for use on the NHS under the provisions of the American Association of State Highway and Transportation Officials (AASHTO) “Manual for Assessing Safety Hardware” (MASH).

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

Decision
The following device was found acceptable, with details provided below:

Description
The test installation consisted of 55.25 meters (181 feet 3 inches) of standard 2.66 millimeters (12-gauge) thick W-beam guardrail supported by steel posts. Anchorage systems similar to those used on tangent guardrail terminals were utilized on both the upstream and downstream ends of the guardrail system. The entire system was constructed with twenty-nine guardrail posts. Post numbers 3 through 27 were galvanized ASTM A36 steel W152 x 13.4 (W6 x 9) sections measuring 1,829 millimeters (6 feet) long. Post numbers 1, 2, 28, and 29 were timber posts measuring 140 millimeters wide x 190 mm deep x 1,080 millimeters long (5.5-inch x 7.5-inch x 42.5-inch) and were placed in 1,829 millimeters (6 feet) long steel foundation tubes. The timber posts and foundation tubes were part of anchor systems designed to replicate the capacity of a tangent guardrail terminal. Post numbers 1 through 29 were spaced 1,905 millimeters (75 inches) on center with a soil embedment depth of 1,016 millimeters (40 inches). The posts were placed in a compacted coarse, crushed limestone material that met Grading B of AASHTO M147-65 (1990) as per MASH. For post numbers 3 through 27, 152-millimeters wide x 305 millimeters deep x 362 millimeters long (6-inch x 12-inch x 14.25-inch) wood spacer blockouts were used to block the rail away from the front face of the steel posts. Standard 2.66 millimeters (12-gauge) thick W-beam rails with additional post bolt slots at half post spacing intervals were placed between post numbers 1 and 29. The following test vehicles were used at indicated guardrail heights:

  1. Test Vehicle 1100C: The W-beam’s top rail height of 813 millimeters (32 inches) with a 657 millimeters (25 7/8-inch) center mounting height.
  2. Test Vehicle 2270P: The W-beam’s top rail height was 787 millimeters (31 inches) with a 632 millimeters (24 7/8 inches) center mounting height.

The rail splices have been moved to the center of the span location. All lap-splice connections between the rail sections were configured to reduce vehicle snag at the splice during the crash test. Design details are provided as enclosure to this correspondence.

Crash Testing
Physical crash test for Test Level 3 as per MASH requires that longitudinal barrier systems be subjected to the following two full-scale vehicle crash tests:

  1. Test Designation 3-10. A 1,100-kg (2,425-lb.) small car impacting the W-beam system at a nominal speed and angle of 100 km/h (62.1 mph) and 25 degrees, respectively.
  2. Test Designation 3-11. A 2,268-kg (5,000-lb.) pickup truck impacting the W-beam system at a nominal speed and angle of 100 km/h (62.1 mph) and 25 degrees, respectively.

Findings
The MGS strong-post W-beam guardrail system was constructed and crash tested. Full-scale vehicle crash tests using a 1100C small car vehicle and a 2270P pickup truck vehicle were performed and was determined to be acceptable according to the TL-3 safety performance criteria presented in MASH. All physical crash test summaries are included as enclosure to this correspondence.

Therefore, the system described in the requests above and detailed in the enclosed drawings is acceptable for use on the NHS 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 letters of acceptance:

 

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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