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                Safety Eligibility Letter WZ-138
  
  **Hardware Type:**
            Work Zone Devices
                          **Code:**
            WZ-138
                          **Date:**
            02/27/2003
                          **Testing Criteria:**
            NCHRP 350
                          **Manufacturer:**
            MDI
                          **Device Description:**
            4884 Breakaway Portable Sign Stand
                          **View PDF:**
            wz138.pdf (602.03 KB)
    
    



February 27, 2003
Refer to:
HSA-10/WZ-138
Mrs.
Kathy Rogalla
Marketing
Displays International
38271
W. Twelve Mile Road
Farmington
Hills, MI  48331-3041
Dear Mrs. Rogalla:
This is in response to your
letter of November 20, 2002, requesting Federal Highway Administration (FHWA)
acceptance of your company's portable breakaway sign stand, MDI Model 4884 as a
crashworthy traffic control device for use in work zones on the National
Highway System (NHS).  Accompanying your
letter was a drawing of the stand.  You
requested that we find this stand 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.” You provided additional
details at our request on January 30 and on February 21, 2003.
Introduction
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
were those lightweight devices which could be self-certified by the vendor,
Category II devices were other lightweight devices which needed individual
crash testing, Category III devices were barriers and other fixed or massive
devices also needing crash testing, and Category IV devices were trailer
mounted lighted signs, arrow panels, etc. 
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 MDI Model 4884 breakaway
portable sign stand is similar to your crash-tested breakaway stand, the MDI
Model 4860. The Model 4860 was found acceptable in our letter WZ-69, dated May
9, 2001.  In your model numbers the
first two digits identify the size of the sign that can be supported and the
second two digits identify the mounting height, both in inches. The Model 4860
was described as follows:
Model 4860, with breakaway
feature, tested with Aluminum panel and light:
This stand is manufactured
with two vertically mounted steel coil springs to support 1219 x 1219 x 2 mm
(48 x 48 x 0.080 inch) aluminum signs. The four legs of the stand are 32 x 32 x
2.5 mm (1.25 x 1.25 x 0.10 inch) square 6061-T6 extruded aluminum tubing. The
coil springs attach the 5 mm (0.19 inch) thick autophoretic coated steel base
to the telescoping upright. The two-piece upright, consisting of a 38
mm (1.50 inch)(bottom) and a 32 mm (1.25 inch)(top) square aluminum tube,
supports the sign. The bottom upright has a scored “breakaway section” at 483 mm (19 inches) above
grade when the stand is fully assembled. Rigid sign mounting brackets support
the aluminum sign at top and bottom and a steel flag lock bracket is attached
to the top upright supporting three hardwood dowel flags. A barricade light
assembly, consisting of a 6-volt battery and a 178 mm (7 inch) polycarbonate lens,
is mounted to the top upright above the flag bracket.  The overall height of the stand, with flags and light is 4115 mm
(162 inches) and 3251 mm (128 inches) without the light and flags. The bottom
of the sign mounts to 1524 mm (60 inches) above
grade. The total weight of the sign stand is 31.6 kg (69.7 pounds) which
includes the stand of 21.7 kg (47.7 pounds), the sign and flags of 8.4 kg (18.5
pounds) and the light of 1.6 kg (3.5 pounds) as tested in MDI 4.
Your current request is for
the Model 4884 breakaway portable sign stand. The Model 4884 is
identical in construction to the Model 4860 with the exception of the mast,
which is in three parts. The bottom section of the Model 4884's mast is
775 mm (30.5 inches) long of 44.5 mm (1.75 inch) square aluminum with a wall
thickness of 2.54 mm (0.10 inch). The middle section is 865 mm (34 inches) long
of 38.1 mm (1.50 inch) square aluminum with a wall thickness of 2.54 mm. The
top section is 1725 mm (68 inches) long of 31.75 mm (1.25 inch) square aluminum
with a wall thickness of 2.54 mm.
Testing and Findings
Full-scale automobile testing
was conducted on the Model 4860 and was found acceptable. The Model 4884 is
similarly constructed, includes the breakaway feature, and mounts the sign
higher above the roadway. The only significant difference is the size of the
lower mast, which is where the breakaway feature (external groove) is found.
Because this could have a material effect on the breakaway performance of the
stand, we asked you to conduct static tests to determine what forces were
needed to activate the breakaway feature. When subjected to horizontal beam
load tests, the 1 1⁄2 inch specimen broke under a static beam load of 1480
pounds. The 1 3⁄4 inch specimen broke at a load of 1760 pounds. The difference of
280 pounds of force was less than a 20 percent increase. After reviewing the
crash tests of the Model 4860 stand we conclude that any delay in the breakaway
action of the larger mass would very likely be offset by the increased height
of the sign and the sign and mass should still pass over the impacting vehicle.
Therefore, the MDI Model 4884 breakaway portable sign stand described above and
detailed in the enclosed drawing is acceptable for use on the NHS under the
range of conditions that the Model 4860 was tested, when proposed by a State.
Please note the following
standard provisions that apply to FHWA letters of acceptance:
Our acceptance is
limited to the crashworthiness characteristics of the devices and does not
cover their structural features, nor conformity with the Manual on Uniform
Traffic Control Devices.
Any changes that may
adversely influence the crashworthiness of the device will require a new
acceptance letter.
Should the FHWA discover
that the qualification testing was flawed, that in-service performance reveals unacceptable safety
problems, or that the device being marketed is significantly different from the
version that was crash tested, it reserves the right to modify or revoke its
acceptance.
You will be expected to
supply potential users with sufficient information on design and installation
requirements to ensure proper performance.
You will be expected to
certify to potential users that the hardware furnished has essentially the same
chemistry, mechanical properties, and geometry as that submitted for
acceptance, and that they will meet the crashworthiness requirements of FHWA
and NCHRP Report 350.
To prevent
misunderstanding by others, this letter of acceptance, designated as number
WZ-138 shall not be reproduced except in full. 
This letter, and the test documentation upon which this letter is based,
is public information.  All such letters
and documentation may be reviewed at our office upon request.
MDI portable sign stands may include patented
components and if so are considered "proprietary." The use of proprietary work zone traffic
control devices in Federal-aid projects is generally of a temporary
nature. They are selected by the
contractor for use as needed and removed upon completion of the project. Under such conditions they can be presumed
to meet requirement "a" given below for the use of proprietary
products on Federal-aid projects. On
the other hand, if proprietary devices are specified for use on Federal-aid
projects, except exempt, non-NHS projects, they:
(a) must be supplied through competitive bidding with equally suitable
unpatented items; (b) the highway agency must certify that they are essential
for synchronization with existing highway facilities or that no equally
suitable alternative exists or; (c) they must be used for research or for a
distinctive type of construction on relatively short sections of road for
experimental purposes.  Our regulations
concerning proprietary products are contained in Title 23, Code of Federal
Regulations, Section 635.411, a copy of which is enclosed.Sincerely yours,
Michael S. Griffith
Acting
Director, Office of Safety Design
Office
of Safety
Enclosure U.S. DEPARTMENT OF TRANSPORTATION

**Federal Highway Administration**

1200 NEW JERSEY AVENUE, SE

WASHINGTON, DC 20590

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