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 / Safety Eligibility Letter

Safety Eligibility Letter CC-114

Download Version
PDF [2,337 KB]

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

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

February 9, 2011

In Reply Refer To: HSST/CC-114

Mr. Geoff Maus
Chief Design Engineer
TrafFix Devices, Inc.
160 Avenida La Pata
San Clemente, California 92673

Dear Mr. Maus:

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: SLED — Sentry Longitudinal Energy Dissipater
Type of system: Gating Crash Cushion/Impact Attenuator
Test Level: NCHRP Report 350 Test Level 3 (TL-3)
Testing conducted by: KARCO Engineering
Date of request: August 31, 2010
Date initially acknowledged: August 31, 2010

You requested that we find this system 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 the Report 350. The FHWA memorandum “ACTION: Identifying Acceptable Highway Safety Features” of July 24, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

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

Description
The SLED End Treatment is a high-density polyethylene (HDPE) water filled crash cushion designed to shield the end of permanent and portable barrier shapes including concrete, steel, and plastic. The SLED End Treatment modules are designed for uni- and bi-directional traffic applications where a gating device is acceptable to the road authority.

The SLED End Treatment modules are designated by their yellow color, each module has overall dimensions of approximately 6.3 ft (1.93 m) × 1.875 ft (.57 m) × 3.8 ft (1.16 m) and weighs approximately 160 lbs empty and 2000 lbs filled. Each module has eleven connecting lugs, five on one end and six on the opposite end. The four upper lugs on every module contain an independent corrosion resistant wire rope. A 1.125 inch (28.6 mm) diameter steel t-pin drops through the 1.5 inch (38 mm) diameter holes in the lugs linking the sections together. At the front of the end treatment, pinned directly to module #1 is the Containment Impact Sled (CIS). The CIS is made of all steel construction with a flat bottom, a curved sheet metal nose, and support frames made of structural rectangular steel tubes. The CIS is designed to attach to either the five or six knuckle ends of module #1. The CIS has a curved impact face to fit over the curved knuckle contour of module #1. The vertical t-pin connects the CIS to module #1 through the series of vertical knuckles and the internal molded-in cables. Module #1 is designed to be an empty module. To prevent module #1 from being filled, six holes are designed into the lower edge of the side walls. Modules 2, 3, and 4 are filled entirely and weigh approximately 2000lbs (907 kg) each when filled.

When the Sentry SLED End Treatment is used to shield an end of an array of Sentry Water Cable Barriers, one CIS, and one module #1 is attached. For TL-3 applications, the SLED End Treatment is attached to a minimum of ten (unlimited maximum number) Sentry Water Cable Barriers.

For shielding all permanent and portable barriers, an adjustable steel transition has been designed. This transition securely attaches the rear of the Sentry SLED End Treatment to the shielded object. The transition is designed to accommodate assorted safety barrier shapes and sizes by using hinged outboard transition panels. The transition panels are made of 0.188 inch (4.8 mm) thick steel, which when attached to the barrier, conforms to the contour of the barrier. The combination of hinging, and contouring, allow the panels allows the SLED End Treatment to be attached to narrow and wide and profile shapes with either converging, or diverging angles, up to 10 degrees. For testing, the contoured hinged panels were anchored to the barriers using a minimum of eight 1 inch diameter anchor bolts with expansion sleeves, minimum four per side.

Crash Testing
A non-redirective gating crash cushion requires the following tests be conducted:
3-40, 3-41, 3-42, 3-43, and 3-44. The following full-scale tests were conducted on the SLED:

Tests for Shielding Sentry Water Cable Barrier
NCHRP-350 Test Number Test Vehicle Weight (kg) Impact Speed (kph) Impact Condition Occ. Imp Velocity (m/s) Ridedown Acceleration (G)
3-40 820 99.6 ¼ offset 10.6 15.7
3-41 2000 102 11.1 11.0
3-43 2000 102.4 15° 8.0 4.8
Tests for Shielding F-Shape CMB Unpinned and Permanently Anchored
NCHRP-350 Test Number Test Vehicle Weight (kg) Impact Speed (kph) Impact Angle Degree Occ. Imp Velocity (m/s) Ridedown Acceleration (G)
3-41 Free Standing 2000 101.5 9.2 9.6
3-41 Anchored 2000 99.1 9.7 12.3
3-44 Anchored 2000 103.1 20° 9.8 10.6
3-44M Anchored 2000 96.2 15° 8.4 15.6

You requested waivers of the following tests:

Test 3-40 -Shielding permanent and portable concrete barriers.
Test 3-42 -Shielding Sentry Water Cable Barrier and permanent and portable concrete barriers.
Test 3-43- Shielding permanent and portable concrete barriers.
Test 3-44 -Shielding Sentry Water Cable Barrier.

You detailed your reasoning behind the waiver requests as follows:

Test 3-40 Shielding Permanent and Portable Concrete Barriers
The Sentry SLED End Treatment shielding Sentry Water Cable Barrier recorded an OIV of 10.6 m/s and a ridedown acceleration of 15.7 g’s. These values are below accepted levels, and were recorded prior to movement of the fourth Sentry module. You expect little or no change in performance with the SLED End Treatment attached to a fixed object.

Tests 3-42 Shielding Sentry Water Cable Barrier and Permanent and Portable Concrete Barriers
You expect the impacting car to push the sled and first empty module aside, allowing the end treatment to act as a gating device, similar to the 3-43 test performed. Just as the 3-43 test had lower measured values than the 3-41 test, we would expect the 3-42 test would have lower values than the 3-40 test.

Test 3-43 Shielding Permanent and Portable Concrete Barriers
As tested, shielding the Sentry Water Cable Barrier, the trajectory of the impacting vehicle carried past the angled barrier and remained upright during and after the collision with only moderate, roll pitch, and yaw. It would be expected that the impacting vehicle would have similar test results regardless of the type of barrier that is being shielded.

Test 3-44 Shielding Sentry Water Cable Barriers
The SLED End Treatment was tested twice in the most severe condition, attached to rigid anchored F-shape safety concrete barrier, in test 3-44 and 3-44M parameters. In these tests, all specified evaluation criteria (C,D,F,K, and N) were met. In addition, evaluation criteria H and I (OIV and Ridedown) were well below the maximum accepted values. Based on the 3-11 performance of Sentry Water Cable Barriers, and the products ability to deflect, you expect equal or better performance for evaluation criteria C,D,F,K and N with the SLED End Treatment attached to Sentry Water Cable Barriers.

All physical crash test summaries are included as enclosures to this correspondence.

Findings
Because the SLED is a non-redirecting, gating cash cushion, it should be applied to hazards that are not likely to be impacted at an angle on the side at any significant velocity. We note also that proper antifreezing agents must be used as filler when the SLED and Sentry products are used in areas where low temperatures can be anticipated. All users of this device should be made aware of the factors that contribute to its proper performance.

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 January 17, 2013.
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