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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter CC-107

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U.S. Department of Transportation
Federal Highway Administration

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

May 18, 2010

In Reply Refer To: HSSD/CC-107

Mr. Pratip Lahiri
Specifications and Standards Section, POD 23
New York State Department of Transportation
50 Wolf Road
Albany, New York 12232

Dear Mr. Lahiri:

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

Name of system: Type IIA Box Beam End Terminal
Type of system: End Terminal
Test Level: Modified MASH TL-3
Testing conducted by: Midwest Roadside Safety Facility
Date of request: November 10, 2009
Date of completed package: April 13, 2010
Request initially acknowledged: November 19, 2009

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 AASHTO MASH. The FHWA Memorandum “Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

Description
The subject Type IIA End Terminal is a re-directive gating end terminal which is used with the New York State generic box beam guiderail (6 in. x 6 in. x 3/16 in. steel tube box beam). The cross section of the end terminal is identical to the generic box beam. The effective length of the Type IIA end terminal is 25 ft., 4 in., which includes a 17 ft., 11 7/8 in. shop-curved section and 8 ft., 3 1/16 in. straight section. The curved section has a radius of 35 ft. and 43 inches of the leading end of the straight section is turned down at a 1:2 slope. The end terminal requires 8 posts which are spaced approximately 3 ft. apart. Enclosure 1 shows the general layout of the New York State DOT Type IIA and details of each component.

Crash Testing
According to MASH, test 3-30 through test 3-38 are to be conducted for end terminals. The point of impact in tests 3-30, 3-31, 3-32, and 3-33 are the face of the ramped part of the end terminal. However, New York State Department of Transportation’s (NYSDOT) intention is to utilize the Type IIA End Terminal at locations where the available clear zone is limited to less than 5 feet behind the leading end of the terminal (e.g., relatively tight radius driveways). Due to the flared design of the end terminal, it is unlikely that a vehicle can collide with the face of the ramped part of the system. Even if such a collision occurs and the vehicle is not contained, the vehicle will enter the hazard free area. Consequently, we agree that these four tests can be waived if the end terminal is properly installed and its use is confined to locations described.

Different variations of the Type IIA end terminal were crash tested by the Midwest Roadside Safety Facility. The variation described above and shown in Enclosure 1 was crash tested according to MASH test 3-34. The test article passed the test. Enclosure 2 shows a summary of the test results.

The point of impact for Test 3-34 is the Critical Impact Point (CIP). By definition, the CIP is where the behavior of the test article changes from redirecting the impacting vehicle to either capturing the vehicle or allowing it to gate through the system. Normally the CIP is determined through detailed analysis of the end terminal or use of relevant computer programs. However, in the test conducted, the CIP was assumed and then verified by a full scale crash test.

Test 3-35 was conducted on a variation of the final Type IIA End Terminal and the test article passed the test (Enclosure 3). The difference between this test article and the final Type IIA end terminal is that post 2 and 4 were moved to the back side of the rail for the final Type IIA End Terminal. This change is not expected to have a significant effect on the performance of the terminal and we concur that the final design would also be expected to pass the test.

A modified version of test 3-35 was also conducted on the end terminal described above because the NYSDOT staff considered the modified test more critical than the test recommended in MASH due to the fact that the end terminal is flared back rather than straight. The difference between the modified 3-35 and MASH 3-35 is the point of impact. In the former, the point of impact was upstream of the beginning of Length of Need (LON) (the fifth post in Enclosure 1) and in the latter it was the beginning of LON. The test article passed the test and Enclosure 4 summarizes the test results.

Test 3-36 is required where the end terminal is attached to rigid barriers or other very stiff features. As long as the Type IIA End Terminal is used with the New York State generic box beam guiderail, this test is not applicable.

Test 3-37 is to examine the behavior of the end terminal during reverse direction impact. This test was not performed. The reason for this is that the device is not intended to be utilized in a location that can result in a reverse direction impact. This acceptance letter is provided with recognition that the described Type IIA End Terminal cannot be installed in locations where there is a potential for reverse direction impacts to encounter the flared /curved portion of the end terminal, such as a median.

Test 3-38 is not required because the subject end terminal does not possess significant attenuation capability.

Findings
The system described 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, and when installed in a manner consistent with the following limitations:

  1. The Type IIA End Terminal is limited to locations where the available clear zone is less than 5 feet behind the leading end of the terminal (e.g., relatively tight radius driveways).
  2. The Type IIA End Terminal cannot be extended beyond an abrupt shoulder break such as a ditch because there is a higher potential for underride in such circumstances.
  3. Because the Type IIA End Terminal was subjected to a reduced MASH test matrix, the use of these terminals should be supervised to ensure that they are not being placed in inappropriate locations. Also, installations shall be monitored to ensure that in-service performance results in improved crash behavior compared to box beam guiderail terminals currently in use.

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

 

Sincerely yours,

/* Signature of David A. Nicol */
David A. Nicol
Director, Office of Safety Design
Office of Safety
Page last modified on January 17, 2013.
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