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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter B-178

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U.S. Department of Transportation
Federal Highway Administration

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

June 5, 2008

In Reply Refer To: HSSD/B-178

Mr. Kevin K. Groeneweg
Mobile Barriers LLC
24918 Genesee Trail Road
Golden, CO 80401

Dear Mr. Groeneweg:

This letter is in response to your request for Federal Highway Administration (FHWA) acceptance of a roadside safety device for use on the National Highway System (NHS).

You requested that we find this device 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” and the proposed American Association of State Highway and Transportation Officials’ Manual for Assessing Safety Hardware – 2008 (MASH-08).

Roadside safety devices should meet the guidelines contained in the NCHRP Report 350, "Recommended Procedures for the Safety Performance Evaluation of Highway Features". FHWA Memorandum “ACTION: Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers. You have also chosen to anticipate the adoption of MASH-08, an option that FHWA has offered with the understanding that additional testing may need to be done if changes to the test criteria are made before MASH-08 is formally adopted.

The Mobile Barrier Trailer (MBT) is an integrated, rigid wall, semi-trailer that is used in conjunction with standard semi-tractors to provide mobile, improved, safety, and work environments for personnel at applicable maintenance, construction, and security sites. It is an extended, mobile, longitudinal barrier that provides a physical and visual wall between passing traffic and the maintenance and construction personnel. With an integrated crash attenuator at the rear, a semi-tractor at the front, and a rigid wall on the side toward passing traffic, the MBT will provide approximately 30.5 m (100 ft) of barrier and protected work area.

The basic trailer is comprised of two platforms and up to three wall sections. The platforms are each 6.4 m (21 ft) in overall length, 2.54 m (100 in) wide and 1.22 m (4 ft) high (riding approximately 1.52 m (5 ft) high with 305 mm (12 in) of ground clearance). The wall sections are each 6.10 m (20 ft) long, 610 mm (24 in) wide, and 1.22 m (4 ft) high (riding approximately 1.52 m (5 ft) high with 305 mm (12 in) of ground clearance). A homogenous 6.4 mm (0.25 in) steel plate is welded to cover the outer side of each wall section. Each wall section abuts up against another of the platforms and is built the same to take an impact from either direction. There. are no snag points at the seams. The outer 6.4 mm (0.25 in) plate and associated welds are ground beveled to transition from one to the other.

Dimensioned illustrations of the trailer are enclosed for reference as "Appendix A."

Crash Testing
One full-scale crash test was conducted using a 2329 kg Dodge, Ram quad cab pickup truck impacting at 23.5 degrees at 102.3 km/hr. The MBT deflected 0.61m (2 ft) during the jmpact. As seen in the enclosed test data summary sheet the evaluation criteria were within the limits specified in MASH-08.

Therefore, the-MBT described above and detailed in the enclosed dimensioned photographs is acceptable for use on the NHS under the range of condhions tested, when allowed by a highway agency. It will be acceptable for TL-2 or TL-3 usage depending on the test level of the Truck Mounted Attenuator that is affixed to the rear.

You subsequently requested that FHW A accept the MASH-08 Test 3-11 as indicative of the NCHRP Report 350 acceptance as well. Because the nature of the MBT device and the impact performance of the MASH-08 pickup truck we can conclude that the MASH-08 Test 10 and the NCHRP Report 350 Tests 10 and 11 can be waived. (The MBT is a semi-rigid vertical wall with relatively low friction characteristics that can be favorably compared to vertical concrete barrier walls that passed prior full-scale testing).

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


Sincerely yours,

Signature of David A. Nicol

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



Test Article

(Contents of Appendix A submitted by Mobile Barriers LLC)


View as assembled with three wall sections

Three wall assembly

Shortened configuration prepared for transport w/ wall sections atop combined platforms.

Shortened configuration

Overall trailer length (with 3 wall sections): 102'
Overall length (with platforms only as shown above - no wall sections installed): 42'
(lengths exclusive of tractor & TMA assembly, not shown)
Width: 100"
Approx Weight: 65,000 lbs with tractor and misc accompaniments
Breakdown:Platforms and rear axel assembly ("caboose") - 20,000 lbs
Wall sections - 5,000 lbs (ea)
Counterweight - 5,000 lbs per wall section
Tractor and accompaniments - 20,000 lbs
Clearance: 9-12" (+ / - 1") depending on configuration
Height to top of platforms (as taped): approx. 5' (58" with 12" of clearance)
Height to top of visual barrier (netting) or wall sections as stored above: approx 9'

Overview (cont)...

Length of platforms (2 shown attached): 21' ea
("caboose" or rear axel assembly under platform opposite tractor)
Length of wall sections (2 shown facing/ion opposite side): 20' ea.
Configuration options: Platform and caboose with 0-3 wall sections
Must be used with an NCHRP Report 350 compliant TMA that has been tested and accepted at TL-3 or such other level such other level as appropriate for applicable traffic speeds and deployment conditions (TMA not shown).


Diagram of length dimensions with 3 wall sections

Dimensions (cont)...

Trailer & Caboose (rear axel assembly) as seen from rear traffic side - wheel cover panel and TMA not shown. (license plate and splashguards blacked out)

Diagram of trailer & caboose

Wall construction...

Diagrams of wall constructions

Platform Construction...

Diagram of platform construction

Platforms connected and loaded for transport, shown open from work side.

Work side

Skeletal view.

Skeletal view

Table 4.1 - Summary of Test Results and Conditions
Images of crash
General Information
Test AgencySouthwest Research Institute
Test NumberMBT-1
Test Date04/03/2008
Test Category3-11 "Update"
Test Article
TypeLongitudinal Barrier
Installation Length30.5 m (100 ft)
Nom. Barrier Height1.52 m (5 ft)
Type of Primary BarrierMobile longitudinal barrier
SoilTest performed on concrete
Test Vehicle
Type½ ton Quad Cab Pickup
Model2002 Dodge Ram 1500 Quad Cab
Mass (kg)2329
Inertial Mass (kg)2329
Dummy Mass (kg)NA
Gross Static Mass (kg)2329
Impact Conditions
Speed (km/hr)102.3
Angle (degrees)23.5
Exit Conditions
Speed (km/hr)80 (calculated)
Angle (degrees)0
Occupant Risk Values
Impact Velocity (m/s)
Ridedown Accelerations (g's)
Test Article Deflection
Dynamic0.61 m (2.0 ft)
Static9.5 cm (3.8 in)
Vehicle Damage
Max. Deform (mm)0
Post Impact Vehicle Behavior
Maximum Roll Angle (degrees)-7.8 @ 0.107 sec.
Maximum Pitch Angle (degrees)2.3 @ 0.447 sec.
Maximum Yaw Angle (degrees)29.3 @ 0.374 sec.

Diagram of crash

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