October 6, 2004
Refer to: HSA-10/WZ-188
Mr. William Snook
The Traffic Safety Store
P.O. Box 33
Chadds Ford, Pennsylvania 19317
Dear Mr. Snook:
This is in response to the letter of August 5, 2004, requesting Federal Highway Administration (FHWA) acceptance of the New SentryTM longitudinal channelizing barricade (LCB) as a test level 1 (TL-1) crashworthy traffic control device for use in work zones on the National Highway System (NHS). It was requested that we find these devices acceptable for use on the NHS based on its similarity to the previously tested "Off-the-Wall" LCB, under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features."
The FHWA guidance on crash testing of work zone traffic control devices is contained in two memoranda. The first, dated July 25, 1997, titled "INFORMATION: Identifying Acceptable Highway Safety Features," established four categories of work zone devices: Category I devices are those lightweight devices which are to be self-certified by the vendor, Category II devices are other lightweight devices which need individual crash testing but with reduced instrumentation, Category III devices are barriers and other fixed or heavy devices also needing crash testing with normal instrumentation, and Category IV devices are trailer mounted lighted signs, arrow panels, etc. for which crash testing requirements have not yet been established. The second guidance memorandum was issued on August 28, 1998, and is titled "INFORMATION: Crash Tested Work Zone Traffic Control Devices." This later memorandum lists devices that are acceptable under Categories I, II, and III.
The New SentryTM LCB units are rotationally molded of low density polyethylene (LDPE) and are 36 inches tall and 48 inches long, weighing 50 pounds empty. The wall thickness is a nominal 0.20 inches. The units are 20 inches wide at the base, tapering to 10 inches wide at the top. They can be filled with up to 100 gallons of water for a total weight of 884 pounds per unit. Patented U-shaped connectors are used to keep adjacent units together and prevent movement during minor hits.
The New SentryTM is comparable in design to the crash-tested LCB, the MB-48x40 Multi-Barrier. The Multi-Barrier LCB units are also rotationally molded of LDPE and are 48 inches tall and 40 inches long, weighing 50 pounds empty. The wall thickness is also 0.20 inches, however the profile is different, ranging from 23 inches wide at the base to 6 inches wide at the top. The Multi-Barrier can also be filled with up to 100 gallons of water. Full-scale automobile testing was conducted on the Multi-Barrier and reported in the FHWA acceptance letter WZ-135 as a TL-1 (50 km/hr) Longitudinal Channelizing Barricade. The crash test matrix was a modification of both the NCHRP Report 350 tests for longitudinal barriers and work zone traffic control devices. The pick up truck and small car crash tests were conducted as if the test article was a redirective barrier, but it was understood that the LCB would allow penetration by the test vehicle. The results are summarized in the table below:
|NCHRP 350 Test #||1-10 (Pick Up Truck)||1-11 (Small Car)|
|Test Article||Off-The-Wall Multi-Barrier MB 48x48|
|Length of test article||30 Sections (30.5 m, 100 ft)||30 Sections (30.5 m, 100 ft)|
|Mass of individual units||22.7 kg (50 pounds)||22.7 kg (50 pounds)|
|Mass of water ballast||418 kg (921 pounds)||418 kg (921 pounds)|
|Vehicle inertial mass||2011 kg (4433 pounds)||826 kg (1820 pounds)|
|Impact speed||51.25 km/h (31.8 mph)||49.16 km/h (30.5 mph)|
|Impact angle||25.0 degrees||20.2 degrees|
|Occupant impact speed||4.78 m/s||6.78 m/s|
|Ridedown acceleration||-3.45 g's||-3.77 g's|
|Trajectory||Vehicle penetrated, stopped||Vehicle penetrated system|
|Vehicle damage||Minor, to grill and hood||Minor, to grill and hood|
|Occup. compartment intrusion||None||None|
|Windshield damage||No Contact||No Contact|
As expected the vehicle penetrated the installation. The occupant impact velocity of the small car exceeded that for a work zone traffic control device, but the occupant impact velocities and accelerations in both tests were within those specified for a barrier. The results of the testing met the unique requirements established for water-filled LCBs and, therefore, were found acceptable for use. You have received permission from Off-the-Wall Products to use the information from the Multi-Barrier crash tests to support the request for acceptance. In addition, it was requested that certain polyethylene plastics from Exxon Chemical Americas or Equistar Chemicals be allowed as alternate materials. We concur in this request, and will retain the product information on file.
We concur in the assertion that the New SentryTM LCB, which is 12 inches shorter in height and 8 inches longer in length than the Multi-Barrier, should perform in similar manner to the tested Multi-Barrier. It was also indicated that this may be considered a temporary situation as Off-the-Wall Products intends to conduct TL-3 testing on the New SentryTM LCB system in the near future. Therefore, the New SentryTM LCB described above and detailed in the enclosed drawings are acceptable for use on the NHS as the NCHRP Report 350 TL-1 device when proposed by a State.
Please note the following standard provisions that apply to the FHWA letters of acceptance:
/Original Signed by/
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety