U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000


Skip to content
FacebookYouTubeTwitterFlickrLinkedIn

Safety

eSubscribe
eSubscribe Envelope

FHWA Home / Safety / Roadway Departure / Eligibility Letter CC-75D

Safety Eligibility Letter CC-75D

Download Version
PDF [1.5 MB]

DOT logo
U.S. Department of Transportation
Federal Highway Administration

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

August 18, 2011

In Reply Refer To:
HSST/CC-75D

Mr. Gerrit A. Dyke, P.E.
Vice President of Engineering and R & D
Barrier Systems, Inc.
3333 Vaca Valley Parkway, Suite 800
Vacaville, CA 95688

Dear Mr. Dyke:

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: Universal TAU-IIR Crash Cushion Systems
Type of system: Redirecting Crash Cushion/Impact Attenuator
Test Level: NCHRP Report 350 Test Levels 2 and 3 (TL-2 and TL-3)
Testing conducted by: Safe Technologies, Inc.
Date of request: December 30, 2010
Date initially acknowledged: January 4, 2011
Task Force 13 designator: SCT 01c

You requested that we find this system, in its various configurations, acceptable for use on the NHS under the provisions of the National Cooperative Highway Research Program (NCHRP) Report 350.

Requirements
Roadside safety devices should meet the guidelines contained in NCHRP Report 350 if tested prior to December 31, 2010. Devices tested after that date must follow the guidelines contained in the American Association of State Highway and Transportation Official's (AASHTO) Manual for Assessing Safety Hardware (MASH). The FHWA memorandum “ACTION: Identifying Acceptable Highway Safety Features” of July 24, 1997, provides further guidance on crash testing requirements of roadside features, including crash cushions.

Decision
The various configurations of the TAU-IIR crash cushion shown in Enclosure 1 are acceptable for use on the NHS at the impact speeds listed.

Description
The TAU-IIR crash cushion uses the same framework as that used in the TAU-II crash cushion configurations that were accepted by the FHWA in letters CC-75 through CC-75C. Specifically, the structural diaphragms, Thrie-beam side panels, slider bolts, backstop assemblies, cables, and anchoring systems are the same as those originally accepted for use on the NHS. The TAU-IIR design uses different energy absorbing cartridges that can be partially self-restoring after some impacts, thereby reducing the need for immediate repairs. These cartridges are made from proprietary hyperelastic (HE) polyurethane and are identified as Type1, 2, or 3 depending on the wall thickness of the cylindrical elements. Dimensions for each type are shown in Enclosure 2. A typical TL-3 installation is shown in Enclosure 3.

Crash Testing
Since only the energy-absorbing elements were changed from the TAU-II design, it was mutually agreed that only the end-on tests were needed to verify acceptable crash performance. Tests were conducted on specific configurations to determine the occupant risk factors for narrow parallel designs, moderately flared designs and wide designs for TL-2 and TL-3 impact speeds. One test was run with an impact speed of 110 km/h (70 mph). Using finite element analysis (FEA) and the results of the full-scale tests that were run, a report prepared by Roadsafe LLC for Barrier Systems, Inc. concluded that the various configurations shown in Enclosure 1were likely to produce acceptable compliance with Report 350 evaluation criteria for end-on impacts. The following summaries describe the tests that were conducted by Safe Technologies, Inc. on specific configurations of the TAU-IIR:

Narrow (parallel) at TL-2
NCHRP Report 350 tests 2-30 and 2-31 were conducted on a narrow unit at 70 km/h (42 mph) to assess the capacity and occupant risk factors associated with a lower speed impact by both test vehicles. For test 2-30, the unit was anchored to an AC base; in test 3-31, a concrete base was used. The TAU-IIR design for both tests consisted of a 4-bay unit with one Type 3 element nose piece, two Type 1 elements in bay 1, and two Type 2 elements in both bays 3 and 4. Enclosures 3 and 4 show the crash cushion design and the test summaries for the small car and the pickup truck, respectively.

Narrow (parallel) at TL-3
Tests 3-31 and 3-32 were conducted on a narrow, parallel-sided 8-bay design. The tested configuration consisted of a Type 3 element nose piece, three bays containing two Type 1 elements per bay, and five bays containing two Type 2 elements per bay. Enclosure 5 shows the tested crash cushion design and the summary sheets for both tests. This tested TL-3 configuration does not use any Type 3 elements in its interior bays.

Narrow (parallel) at TL-3
Test 3-30 was conducted on a narrow, parallel-sided crash cushion to determine its crashworthiness at an impact speed of 110 km/h (70 mph). The tested configuration was a 10-bay unit, consisting of a Type 3 nose piece, three bays containing two Type 1 elements per bay, four bays containing two Type 3 elements per bay, and three bays containing two Type 2 elements per bay. Enclosure 6 shows the tested design and the crash test summary sheet.

Flared at TL-3
Test 3-31 was conducted to verify the crashworthiness of a flared side-panel layout. The TAU-IIR configuration tested was a seven bay design consisting of a Type 3 nose piece, three bays containing two Type 1 elements per bay, one bay containing two Type 2 elements, and three bays containing four Type 2 elements per bay. Enclosure 7 shows the tested design and the crash test summary sheet.

Wide (flared) at TL-3
Tests 3-30 and 3-31 were conducted on a wide-flared unit. The tested design was a 7-bay unit with a Type 3 nose piece, three bays containing two Type 1 elements per bay and four bays containing four tyle2 elements per bay. Enclosure 8 shows the tested design and the crash test summary sheet.

Findings
Based on our review of the information you submitted, the TAU-IIR designs described above and detailed in the enclosed drawings are acceptable for use on the NHS under the range of conditions tested, when such use is acceptable to a highway agency. In addition, any of the configurations depicted in Enclosure 1 are also acceptable for use on the NHS. The five TAU-IIR configurations that were crash-tested were used to validate the FEA model from which the “family” of designs was created. In comparing the model results to the full-scale crash tests, it was seen that the model predictions were almost always conservative (i.e., they over-predicted the occupant risk factors). Consequently, the non-tested TAU-IIR configurations may be used with confidence that they will perform acceptably under the impact speeds listed.

Transportation agencies specifying the 10-bay 110 km/h (70 mph) design should be advised that this unit met all NCHRP Report 350 evaluation criteria only for a head-on impact with the 2000P pickup truck at that speed. The remaining high-speed configurations were developed through analysis and should be equally acceptable for the head-on crash with the pickup truck. However, no assumption should be made that the remaining Report 350 tests for a crash cushion would meet all appropriate evaluation criteria at a 110 km/h (70 mph) impact speed. There is no federal requirement to specify crash cushions that exceed TL-3 capacity.

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

 

Sincerely yours,

Signature of George E. Rice, Jr.

Michael S. Griffith
Director, Office of Safety Technologies
Office of Safety

Enclosures

Page last modified on February 12, 2016
Safe Roads for a Safer Future - Investment in roadway safety saves lives
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000