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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter CC-106

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U.S. Department of Transportation
Federal Highway Administration

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

December 23, 2009

In Reply Refer To:
HSSD/CC-106

Mr. Andy Keel, P.E.
Roadway Design Standards Engineer
605 Suwannee Street, MS 32
Tallahassee, FL 32399-0450

Dear Mr. Keel:

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

Name of device: Florida Low-Profile Barrier Terminal
Type of device: End Terminal
Test Level: TL-2
Testing conducted by: E-Tech Testing Services, Inc., Rocklin, CA
Date of request: October 19, 2009
Date initially acknowledged: October 19, 2009
Date of completed package: November 27, 2009
Task Force 13 Designator: SER-04

You requested that we find this device 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.”

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.

Description
The Florida Low-Profile work zone concrete (low-profile) barrier was earlier approved for use on the NHS as per FHWA Acceptance Letter HSA-10/B-115 dated August 12, 2003. The height of this low profile barrier is 18 inches. A study was conducted of existing end terminals successfully tested as per NCHRP 350 to specify with this low-profile barrier. This study revealed all end terminals were taller than 18inches. Furthermore, none of the end terminals researched were compatible with the unique barrier-to-barrier connection system used by this low-profile barrier system. Upon impact this connection will simultaneously engage adjoining barrier segments. Barrier resistance in both inertial mass and contact surface friction serves to redirect the Test Level 2 (TL-2) impact force without requiring any positive mechanical anchorage to the roadway surface (e.g. vertical steel pins). This low-profile barrier also serves in providing an unobstructed driver view of cross-traffic.

The following design goals were established to develop a new end terminal for the Florida low-profile barrier.

In addition, it was also determined that a barrier height of less than 18in. would not provide the necessary level of safety with regard to vehicle redirection and resistance to vehicle rollover. Therefore there exists a diminished likelihood the tapered end terminal will successfully redirect a full-size pickup truck. For this reason, no part of the end terminal is considered to contribute to the required length of need (LON) of barrier to protect a particular work zone.

The end terminal is 20ft. long. It is composed of two sections, (1) 12-ft. long reinforced concrete segment and (1) 8-ft. steel segment. The end terminal height varies from 18 inches at the point of connection to the low-profile barrier, tapering to 2 inches at the end of the end terminal. An innovative connection system and a nearly symmetric shape make the end terminal reversible. This reversibility permits the end-treatment to be attached to either the key or keyway ends of low‑profile barrier segments. Neither the end terminal nor the low-profile barrier to which it attaches requires any mechanical anchorage to the roadway surface. This design was completed using a combination of numerical finite element impact simulation followed by full-scale crash tests per the requirements of NCHRP Report350. The finite element impact analysis was used to establish the geometric shape of the end terminal and to quantify design forces.

Crash Testing
Full-scale crash tests conducted on the Florida low-profile barrier (Consolazio etal.2003) were carried out in accordance with the longitudinal barrier requirements of NCHRPReport350. Testing was conducted at TL-2 conditions (45mph impact speed), hence the design and testing of the end terminal shall also correspond to 45mph impact conditions. The newly developed end terminal shall be designed and tested as a gating terminal device. The following crash tests are required as per NCHRP Report 350 for a gating end terminal (descriptions have been adapted from Beason et al. 1998):

Findings
Using simulation and physical crash testing, a new crashworthy end terminal was developed for specification with the Florida low-profile barrier system. Based on results obtained from separate simulations, the minimum required lateral deflection space that provides adequate barrier performance in drop-off zone applications is 6in. for an impact speed of 45 mph. Subsequently, the end terminal was structurally-designed, fabricated, and subjected to a series of seven full-scale crash tests per the TL-2 requirements of NCHRP Report 350. Crash tests involving both a small car (820kg) and a full-size pickup truck (2000 kg) were successfully passed. The test data summary sheets are enclosed for reference.

Therefore, the device described in the request above and detailed in the enclosed drawings is acceptable for use on the NHS under the range of conditions tested, when acceptable to a highway agency.

Standard provisions

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

Enclosures

Page last modified on January 17, 2013.
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