Refer to: HSA-10/WZ-115

Mr. Henry Ross
United Rentals Highway Technologies
P.O. Box 7050
Villla Park, Illinois  60181-7050

Dear Mr. Ross:                                                                                                                                    

Thank you for your letters of January 29 and March 15, 2002, requesting Federal Highway Administration (FHWA) acceptance of your company's portable sign trailer as a crashworthy traffic control device for use in work zones on the National Highway System (NHS).  Accompanying your letter was a letter report of crash testing conducted by E-Tech testing services and a video of the tests.  You requested that we find these devices 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.”  On April 5, 2002, in response to our request, you provided additional information via the Internet.


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 trailer consists of 2 x 2 inch square steel (ASTM A-500, Grade B) tubing with a wall thickness of 1/8 inch.  Two 14 inch diameter wheels are affixed to the axle, which is 45 inches long.  The tongue is 6 feet long. The 2 inch diameter steel pipe mast is six feet in length and carries a framework that supports signs up to 51 inches wide.  The mast is slides into a 2-˝ inch diameter pipe, which is affixed to a hinged connection that, along with the overall trailer design, is illustrated in the enclosed drawings for reference.  The overall weight of the trailer and sign is 220 pounds (99.8 kg).


Full-scale automobile testing was conducted on your company's devices.  Two stand-alone  examples of the device were tested in separate impacts.  One was struck head-on and the other was impacted at 90 degrees. The complete device as tested is shown in Enclosure 1.  The crash test is summarized in the table below:

Test Number



Test Article

United Rental Portable Sign Trailer




Height to Bottom of Sign

1276 mm (50 in)

1276 mm  (50 in)

Height to Top of Sign

2800 mm (110 in)

2800 mm (110 in)

Flags or lights



Test Article Mass (each)

99.8 kg

99.8 kg

Vehicle Inertial Mass

819 kg

816 kg

Impact Speed

101.8 km/hr

99.7 km/hr

Velocity Change

3.9 m/s

3.9 m/s

Occupant Impact Speed

3.9 m/s

3.9 m/s

Vehicle crush


Roof crush

Occupant Compart. Intrusion


Sign edge entered vehicle

Windshield Damage

No Contact



This trailer is somewhat similar to one crash-tested at the Federal Outdoor Impact Laboratory for the State of Montana.  The Montana trailer was judged acceptable for use in FHWA Acceptance Letter WZ-19 dated July 26, 1999.  The Montana trailer was also tested via two impacts, at zero and 90 degrees respectively.  There was a significant difference in the testing procedure, however, in that the sign panel was oriented perpendicular to the direction of vehicle travel in both impacts of the Montana trailer, causing the face of the sign to impact the vehicle in both tests.  In testing the UR trailer, the entire rig, sign and all, was turned through an angle of 90 degrees.  This resulted in the edge of the sign facing the test vehicle in the second test.

Apparently the testing of the Montana trailer was conducted in this manner because it was known that the leading edge of an end-on sign would be very likely to cause severe damage. 

It was also recognized that these sign trailers are removed at the end of the workday.  Therefore,  the situation where the sign is turned 90 degrees in order to obscure the message from drivers does not occur.

The URL trailers were tested with the sign blank oriented perpendicular to the trailer tongue in both tests.  In the second test the thin edge of the sign penetrated the windshield and caused extensive roof damage.  If the second test had been run with the sign perpendicular to the windshield it is expected that the results would be comparable to those of the Montana trailer.

The results of the testing met the FHWA requirements except as noted and, therefore, the devices described above and shown in the enclosed drawings for reference are acceptable for use on the NHS under the range of conditions tested, when proposed by a State.  The failing results of the second test are an indication that the trailer should never be left with the sign oriented parallel to traffic.  The design of the United Rentals trailer incorporates a hinge base feature that makes it relatively easy to obscure the message of the sign when it is no longer appropriate.

Please note the following standard provisions that apply to FHWA letters of acceptance:

The United Rentals trailer 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,

Carol H. Jacoby, P.E.

Director, Office of Safety Design