U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Ave. S.E.
Washington, D.C. 20590
November 14, 2008
In Reply Refer To: HSSD/B-182
Mr. Scott K. Rosenbaugh
Research Associate Engineer
Midwest Roadside Safety Facility
University of Nebraska-Lincoln
527 Nebraska Hall
Lincoln, Nebraska 38588-0529
Dear Mr. Rosenbaugh:
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: | Vertical-Faced, Concrete Median Barrier Incorporating Head Ejection Criteria |
|---|---|
| Type of system: | Concrete Median Barrier |
| Test Level: | NCHRP Report 350 TL 5 & MASH-08 TL 5 |
| Testing conducted by: | Midwest Roadside Safety Facility |
| Date of request: | February 27, 2008 |
| Date of completed package: | October 14, 2008 |
You requested that we find this system acceptable for use on the NHS under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 “Recommended Procedures for the Safety Performance Evaluation of Highway Features” and the proposed American Association of State Highway and Transportation Officials’ Manual for Assessing Safety Hardware 2008 (MASH-08).
Requirements
Roadside safety systems should meet the guidelines contained in the NCHRP Report 350, "Recommended Procedures for the Safety Performance Evaluation of Highway Features". FHWA Memorandum “ACTION: Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers. You have also chosen to anticipate the adoption of MASH-08, an option that FHWA has offered with the understanding that additional testing may need to be done if changes to the test criteria are made before MASH-08 is formally adopted.
Description
This concrete median barrier is intended to safely redirect vehicles ranging from small cars to fully-loaded tractor trailers, while (1) maximizing stability in passenger vehicles by limiting wheel climb and roll, (2) addressing occupant safety by limiting peak impact forces, (3) preventing head slap, and (4) providing an economical alternative to existing concrete barrier designs. The profile of the upper 8 inches of the barrier is set back to accommodate a “head ejection envelope” which was determined through an analysis of previous full-scale crash tests involving passenger vehicles impacting vertical-faced barriers and other rigid concrete barriers.
The geometry of this setback directly applies only to rigid barriers with a vertical or near vertical face, and for belted occupants meeting the measurements of the Hybrid III 50 and 95 percentile male dummies. The final barrier cross section design is shown in the drawings which are enclosed for reference. Also shown is the barrier end section with a footer whose function is to provide sufficient torsion resistance to match the overturning moment of the end section.
Crash Testing
Full-scale crash testing was conducted with a tractor-trailer rig having a test inertial weight of 36,154 kg (79,538 pounds) following NCHRP Report 350 Test 5-12 and MASH-08 Test 5-12. The enclosed test data summary page shows the impact velocity was 84.9 km/hr (55.7 mi/hr) at an angle of 15.4 degrees. During the impact, the maximum roll angle of the truck was 22.8 degrees. Although the dynamic deflection of the barrier was negligible (38 mm, or about 1.5 inches), the “working width” considering the incursion of the box over the top of the barrier was 1894 mm (75 inches).
Findings
The concrete median barrier adequately contained and redirected the vehicle without permanent displacements of the barrier. Vehicle roll, pitch, and yaw angular displacements were deemed acceptable, because they did not adversely influence occupant risk safety criteria nor cause rollover. After collision, the vehicle rode down the face of the barrier and did not intrude into adjacent traffic lanes. Thus, the vehicle’s exit angle was less than 60 percent of the impact angle. Therefore, test TL5CMB-2 conducted on a concrete median barrier was determined to be acceptable according to the TL-5 safety performance criteria found in NCHRP Report 350. Note, the test also satisfies all evaluation criteria for test 5-12 found in MASH-08.
Therefore, 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.
As NCHRP Report 350 does not have mandatory evaluation criteria regarding vehicle occupants contacting the hardware outside of the occupant compartment, this letter is limited to accepting the performance as a median barrier to contain and redirect vehicles, with no implication that head ejection criteria is a requirement. However, MASH-08 does identify the safety risk involved with occupants extending out of the vehicle and coming into direct contact with the test article in Section 4.2.1.5, Paragraph 2. This guidance recommends that dummies are to be placed in the front seat on the impact side of passenger vehicles during tests of longitudinal barriers taller than 33 inches. Although a passenger vehicle test was not performed, the barrier geometry was designed to prevent such occupant-barrier contact.
Please note the following standard provisions that apply to the FHWA letters of acceptance:
Sincerely yours, /signed for/ David A. Nicol |
