400 Seventh St., S.W. 

Washington, D.C. 20590

May 26, 2005 

In Reply Refer To: HSA-10/B-135 

Ronald K. Faller, Ph.D., P.E. 

Research Assistant Professor 

Midwest Roadside Safety Facility (MwRSF) 

University of Nebraska-Lincoln 

527 Nebraska Hall 

P.O. Box 880529 

Lincoln, Nebraska 68588-0529 

Dear Dr. Faller: 

In your March 28 letter, you requested formal Federal Highway Administration acceptance of a 

timber rub-rail developed to shield a noise wall used by the Minnesota Department of 

Transportation (MnDOT). To support your request, you also sent me copies of the Midwest 

Roadside Safety Facility’s March 8 test report entitled “Design and Evaluation of Minnesota’s 

Timber Rub-Rail for Noise Barriers” and digital videos of the test you conducted. 

The rub-rail and spacer block design consisted of treated glulam timber made from Southern 

Pine. The rail element was 13.5-in. high x 8.75-in. deep with a top mounting height of 30 in. 

The spacer blocks were 9-in. wide x 6-in. deep x 13.5 in. high and bolted on 8-ft. centers to the 

12-in. x 18-in. reinforced concrete posts that formed the framework for the noise barrier. The 

reinforced concrete posts were 16-ft long and utilized a 6-ft embedment depth. Enclosure 1 

provides drawings of the test installation. I assume that anyone interested in obtaining 

complete system drawings that include the connection hardware and mounting details and 

specifications can request them directly from MnDOT. You conducted the NCHRP Report 

350 test 3-11 (MNTR-1) and reported that all Report 350 evaluation criteria were met. Based 

on these test results, summarized in Enclosure 2, I agree that this design, when used with 

MnDOT’s noise wall or with a design structurally and geometrically similar, can be used on 

the National Highway System as a test level 3 barrier, assuming it is introduced outside the 

minimum clear zone for the highway facility or its approach end is adequately shielded from

traffic. 

I noted that the crash test was conducted without the noise wall panels installed on the posts. 

Since these horizontal panels are fabricated from small timber planking, they were not believed 

to degrade the system’s safety performance. Staff members have suggested that installing the 

 
2

timber rail on steel posts driven directly in front of the concrete noise wall columns (but not 

physically attached to them), would simplify construction and provide some additional 

overhang distance before vehicular contact with the columns would occur. This modified 

design would allow more flexibility in the lateral placement of the timber noise wall panels as 

well since there appears to be little likelihood that panels recessed beyond the traffic face of the 

concrete columns would pose a spearing problem. 

Sincerely yours, 

 

John R. Baxter, P.E. 

 Director, Office of Safety Design 

 Office of Safety 

2 Enclosures 


40

0.000 sec 0.054 sec 0.118 sec 0.222 sec 

! Test Number . . . . . . . . . . . . . . . . . . MNTR-1! Date . . . . . . . . . . . . . . . . . . . . . . . . 7/16/04! Appurtenance . . . . . . . . . . . . . . . . . Minnesota’s Timber Rub Rail for 

Noise Barriers

! Total Length . . . . . . . . . . . . . . . . . . 24.86 m! Glulam Wood Rail

Material . . . . . . . . . . . . . . . . . . Southern Pine, Combination No. 48Dimensions . . . . . . . . . . . . . . . 343 mm x 222 mm by 24.86 m longTop Mounting Height . . . . . . . 762 mm

! Post Nos. 1-11

Material . . . . . . . . . . . . . . . . . . ConcreteDimensions . . . . . . . . . . . . . . . 305 mm x 457 mm by 4,877 mm longEmbedment Depth . . . . . . . . . 1,829 mmSpacing . . . . . . . . . . . . . . . . . . 2,438 mm

! Wood Spacer Blocks Nos. 1-11

Material . . . . . . . . . . . . . . . . . . Southern Pine, Combination No. 48Dimensions . . . . . . . . . . . . . . . 229 mm x 152 mm by 343 mm long

! Vehicle Model . . . . . . . . . . . . . . . . 1999 GMC 2500 3⁄4-ton pickup

Curb . . . . . . . . . . . . . . . . . . . . 1,981 kgTest Inertial . . . . . . . . . . . . . . . 1,989 kgGross Static . . . . . . . . . . . . . . . 1,989 kg

! Vehicle Speed

Impact . . . . . . . . . . . . . . . . . 99.4 km/hExit . . . . . . . . . . . . . . . . . . . 57.4 km/h

! Vehicle Angle

Impact . . . . . . . . . . . . . . . . . . . 25Exit . . . . . . . . . . . . . . . . . . . . . . 4.1 

! Vehicle Snagging . . . . . . . . . . . . . . . M! Vehicle Pocketing . . . . . . . . . . . . . . . No! Vehicle Stability . . . . . . . . . . . . . . . . Sa! Occupant Ridedown Deceleration (10 mse

Longitudinal . . . . . . . . . . . . . . . 8.4Lateral (not required) . . . . . . . . 9.7

! Occupant Impact Velocity

Longitudinal . . . . . . . . . . . . . . . 8.9Lateral (not required) . . . . . . . . 6.8

! PHD . . . . . . . . . . . . . . . . . . . . . . . . . 10! THIV . . . . . . . . . . . . . . . . . . . . . . . . . 11! Vehicle Damage . . . . . . . . . . . . . . . . M

TAD4 . . . . . . . . . . . . . . . . . . . . 1-R

SAE5 . . . . . . . . . . . . . . . . . . . . . 1-F

! Vehicle Stopping Distance . . . . . . . . 39

1.4

! Barrier Damage . . . . . . . . . . . . . . . . . M! Maximum Rail Deflections

Permanent Set . . . . . . . . . . . . . 55 Dynamic . . . . . . . . . . . . . . . . . . 92 

! Working Width . . . . . . . . . . . . . . . . . 1,1

Figure 22. Summary of Test Results and Sequential Photographs, Test MNTR-1