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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter B-193 (REVISED)

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U.S. Department of Transportation
Federal Highway Administration

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

May 29, 2009

In Reply Refer To:
HSSD/B-193
(REVISED)

Mr. Rick Mauer
Outside National Sales Representative
Nucor Steel Marion
P.O. Box 837
Greenland, NH 03840

Dear Mr. Mauer:

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:Nu-Cable 4-Cable Median Barrier on 1V:4H Slopes
Type of system:Median Cable Barrier (TL-4 design)
Test Level:NCHRP Report 350 TL-3
Testing conducted by:Texas Transportation Institute and Holmes Solutions
Date of request:April 9, 2009
Date of completed package:May 18, 2009

You requested that we find this Test Level 4 (TL-4) median cable system acceptable for use on the NHS on 1V:4H slopes under TL-3 conditions of the National Cooperative Highway Research Program (NCHRP) Report 350 “Recommended Procedures for the Safety Performance Evaluation of Highway Features.”

Requirements
Roadside safety systems should meet the guidelines contained in the NCHRP Report 350. FHWA Memorandum “Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

Description
The Nucor 4-Cable Nu-Cable TL-4 wire rope barrier system consists of the following components:

All steel line posts were AASHTO designator CLP-06 Rib-Bak 4-pounds-per-foot (6-kg/m) cable line posts, manufactured from 80,000-psi (552-MPa) yield / 100,000-psi (690-MPa) tensile hot rolled steel. The posts were perforated full length with 3/8-in (9.5-mm) holes on 1-in (25-mm) centers. The overall length of the line posts was 5 ft, 3 in (1600 mm). The line posts were placed inside HDPE (high density polyethylene) plastic or steel sockets which were cast into 12-in (300-mm) by 30-in (750-mm) reinforced concrete foundations.

The restraints consisted of four cables constructed using 3/4-in (19-mm) 3 x 7 strand galvanized pre-stretched cable with a breaking strength in excess of 36,800 lbs (16,700 kg). The actual cable breaking strength was approximately 41,500 lbs (18,825 kg). The cables were tensioned to a nominal 5600 lbs (25 kN) at an ambient temperature of 70°F (21°C). The cables were designed to be placed at heights of 18.5 in (470 mm), 30.5 in (770 mm), 38.5 in (980 mm) and 41.5 in (1065 mm) above ground. The actual placement varied minimally between the three tests due to construction tolerance of plus or minus 2 in (50 mm). The top and bottom cables were placed on the side of the post closest to traffic while the two middle cables were on the ditch side.

The posts were located in a line, offset 4 ft (1220 mm) horizontally and 12 in (305 mm) vertically below the top edge of the backslope of the depressed median placing them 11 ft (3350 mm) from the centerline of the median ditch. The line post spacing was 20 ft (6.1 m). The soil was NCHRP Report 350 “Standard” soil.

All cable terminations used cable grip fittings which consisted of three tapered ‘jaws’ that fit inside a tapered casing and a tail piece screwed into the rear of the casing. The cable tension adjustment was achieved with turnbuckle-like devices, fabricated from 3/8-in (10-mm) x 3/4-in (20-mm) low tensile steel side arms, welded to 1 1/8-in (30-mm) thick end-washers.

A top clip was used to secure the top two cables (cables 1 and 2) to the steel line posts. The clip was fabricated from 3/4-in (19-mm) x 1/4-in (6-mm) mild steel flat. The clip is retained by a triangular shaped band manufactured from 0.1-in (2.4-mm) flat steel, folded and spot welded together at the ends. Two locking hook bolts were used to secure the lower two cables (cables 3 and 4) to the steel line posts. The locking hook bolts were manufactured from 5/16-in (8-mm) steel rod.

Crash Testing
Three tests were performed in order to capture the “worst practical conditions”. All of the tests were performed in 30-ft wide ditches. The overall length of the runs tested were all approximately 340 ft (104 m). The critical impact point (CIP) was chosen to have the impact occur directly on a line post.

  1. NCHRP Report 350 Test Designation 3-10 [TTI Test # 400001-NSM11]
    An 1808-lb (820-kg) passenger car impacted the critical impact point (CIP) of the length-of-need (LON) at 61.8 mph (99.5 km/h) and 21.4 degrees. The impact occurred on the near side of the 1V:4H slope with the barrier located 4 ft (1220 mm) down from the breakpoint. The vehicle engaged all four cables, with the top cable contacting the “A” pillar and causing a 1.8-inch (46-mm) tear in the windshield before sliding briefly up onto the roof. The test vehicle was smoothly redirected parallel to the barrier and remained upright.

  2. NCHRP Report 350 Test Designation 3-10 [Holmes Solutions Test # 102350.01-3]
    An 1808-lb (820-kg) passenger car was directed towards the CIP of the LON at 63.9 mph (102.8 km/h) and 20 degrees. The impact occurred on the far side 1V:4H slope with the barrier located 11 ft (3350 mm) beyond the centerline of the median ditch. The test vehicle initially impacted near the base of the slope, slowing the vehicle such that the subsequent impact with the test article occurred at a speed of 55.9 mph (89.9 km/h). The front of the vehicle engaged all four cables with no contact in the windshield area, and was redirected upright.

  3. Manual for Assessing Safety Hardware (MASH) Test Designation 3-11
    [TTI Test # 400001-NSM10]
    A 5100-lb (2313-kg) quad cab pickup truck impacted the CIP of the LON at 63.2 mph (101.7 km/h) and 26.6 degrees. The impact occurred on the near side of the 4:1 slope with the barrier located 4ft (1220 mm) down from the breakpoint. The test vehicle engaged all four cables and was smoothly redirected parallel to the barrier while remaining upright. The maximum dynamic deflection was 9.6 ft (2.93 m).

The test data summary sheets for these three tests are enclosed for reference.

Findings
The results of the 3-10 tests conducted under the guidance of NCHRP Report 350 and the 3-11 test conducted under the guidance of MASH met the respective test and evaluation criteria with the exception of the test article length. We considered allowing the use of the NCHRP Report 350 Test 3-10 (with a lighter small car) and the MASH Test 3-11 (with the heavier pickup truck) to represent the “worst case scenario” for qualifying the device to be compliant under both Report 350 and MASH. We agreed with you prior to the testing that you could submit this request under both criteria, however the 3-11 test using the quad cab pickup truck was conducted on an installation of 343 feet of barrier which does not meet the MASH minimum of 600 feet. Therefore, the system described above and detailed in the enclosed drawings is acceptable for use on 1V:4H median slopes on the NHS under the range of conditions tested agreeable to NCHRP Report 350 only, 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 David A. Nicol

David A. Nicol, P.E.
Director, Office of Safety Design
Office of Safety

Enclosures

Page last modified on June 24, 2011.
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