March 11, 2003
Mr. Albert W. Unrath Sr.
ALBERT W. UNRATH, INC.
PO Box 317
Line Lexington, PA
Dear Mr. Unrath:
In your December 27, 2002 letter to Mr. Frederick G. Wright,
Jr., former Director of the Office of Highway Safety, you requested the Federal
Highway Administration's (FHWA) acceptance of a modified U-MAD truck mounted
attenuator (TMA) at the National Cooperative Highway Research Program (NCHRP)
Report 350 test level 1 (TL-1). The Federal Highway Administration has
previously accepted both a TL-2 unit (U-MAD 70K) with a length of 7.5 feet and
a TL-3 unit (U-MAD 100K) a total length of approximately 10 feet with for use
on the National Highway System.
The modified TMA design, called the U-MAD 50K, consists of
an aluminum box with internal compartments filled with variable density
energy-dissipating material. The first
24 inches is comprised of the softest material, followed by 21 inches of a
stiffer material, and ending with 3 inches of a yet stiffer composition. The unit is rectangular, measuring 1220-mm
(48-in) long by 2286-mm (90 inches) wide.
It is 711-mm (28-in) deep and is 317 mm (12.5 in) above the roadway
surface when deployed.
To support your request, you included an analysis of the
results of your earlier 70 km/h and 100 km/h tests and extrapolated these
results to the shorter TL-1 design.
Since the impact energy to be dissipated in a 50 km/h test is
approximately half that in a 70 km/h impact and the first two feet of all three
designs consists of the same crushable material, followed by 18 or 21 inches of
a stiffer material, I agree that the U-MAD 50K would likely meet the evaluation
criteria for an NCHRP Report 350 TMA at the TL-1 speed of 50 km/h. Therefore, it may be used on the National
Highway System (NHS) when such use is deemed appropriate by the contracting
authority when expected impact speeds are near or less than 50 km/h.
Please note the following standard
provisions that apply to FHWA letters of acceptance:
acceptance is limited to the crashworthiness characteristics of the
devices and does not cover their structural features, durability, or
conformity with the Manual on Uniform Traffic Control Devices.
changes that may adversely influence the crashworthiness of the device
will require a new acceptance letter.
the FHWA discover that in-service performance reveals unacceptable safety
problems, or that the device being marketed is significantly different
from the version that was accepted for use on the NHS, it reserves the
right to modify or revoke its acceptance.
will be expected to supply potential users with sufficient information on
design and installation requirements to ensure proper performance.
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.
prevent misunderstanding by others, this letter of acceptance, designated
as number CC64C shall not be reproduced except in full. This letter, and the documentation upon
which this letter is based, is public information. All such letters and
documentation may be reviewed at our office upon request.
U-MAD50K includes patented components and is considered to be a
proprietary device. 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 has been previously provided for your ready reference.
(original signed by Michael S. Griffith)
Director, Office of Safety Design