1200 New Jersey Ave., SE

 Washington, D.C. 20590

August 19, 2011 

In Reply Refer To: 

HSST/ B-41A 

Mr. Robert Bielenberg

Research Associate Engineer

Midwest Roadside Safety Facility

130 Whittier Research

2200 Vine Street 

Lincoln, NE 68583-0853 

Dear Mr. Bielenberg: 

This letter is in response to your request for the Federal Highway Administration (FHWA) 

acceptance of a roadside safety system for use on the National Highway System (NHS).

Name of system: End-to-End Approach Transition between F-shape Temporary Concrete 

Barrier and Permanent Concrete Median Barrier

Type of system: Thrie Beam Transition

Test Level: AASHTO Manual for Assessing Safety Hardware (MASH) Test Level 3

Testing conducted by: Midwest Roadside Safety Facility

Date of request: December 28, 2010

You requested that we find this system acceptable for use on the NHS under the provisions of the 

American Association of State Highway and Transportation Officials (AASHTO) “Manual for 

Assessing Safety Hardware” (MASH).

Requirements 

Roadside safety devices should meet the guidelines contained in the MASH.

Decision

The following device was found acceptable, with details provided below: 

• Thrie Beam Transition between F-shape Temporary Concrete Barrier and Permanent 

Concrete Median Barrier

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Description

The following combinations of barrier were researched to determine the type of permanent 

concrete barrier that would be the most critical when used in an approach transition. To make 

this determination, the shapes of various permanent median barrier designs were compared to the 

shape of both the narrow and wide versions of the 32 inches (813 millimeters) tall F-shape 

temporary barrier. The following comparisons were completed: 

1. 32-inch (813- millimeter) F-shape temporary barrier to 32-inch and 42-inch (813- millimeter 

and 1,067- millimeter) F-shape and New Jersey (NJ) -shape median barriers,

2. 32-inch (813- millimeter) F-shape temporary barrier to 32-inch and 42-inch (813- millimeter 

and 1,067- millimeters) Texas (TX) and California (CA) single-slope median barriers,

3. 32-inch (813- millimeter) F-shape temporary barrier to 32-inch and 42-inch (813- millimeter 

and 1,067- millimeter) vertical median barriers,

4. 32-inch (813- millimeter) wider F-shape temporary barrier to 32-inch and 42-inch (813- 

millimeter and 1,067-millimeter) F-shape and NJ-shape median barriers, 

5. 32-inch (813- millimeter) wider F-shape temporary barrier to 32-inch and 42-inch (813- 

millimeter and 1,067- millimeter) TX and CA single-slope median barriers,

6. 32-inch (813- millimeter) wider F-shape temporary barrier to 32-inch and 42-inch (813- 

millimeter and 1,067- millimeter) vertical median barriers.

From the comparison of the various shapes, it was determined that the 42 inches. (1,067 

millimeters) tall CA single-slope median barrier provided the worst case situation. Comparison 

of the F-shape temporary barrier geometry with the single-slope barrier showed that there was a 

high potential for vehicle snag on the sides of the permanent barrier as well as on the 10 inches 

(254 millimeters) height difference of the barriers. It was determined that shifting the temporary 

barrier toward the traffic-flow side of the single-slope so that the slope breakpoint at the top of 

the toe of the temporary barrier lines up with the traffic-side face of the permanent single slope 

would help alleviate some of the snag potential on the single-slope barrier. This asymmetrical 

placement would only present a safety concern if the temporary barrier were used to separate 

traffic flowing in the same direction, such as in a gore area. However, it was believed that this 

situation would be better treated with a barrier end treatment.

The 166 feet 10inches (50.9 meters) long test installation details for a transition from temporary 

concrete barriers to a permanent concrete barrier are shown in Figures 4 through 20. The test 

installation consisted of a rigid parapet, four transition barriers, eight free-standing barriers on 

the upstream end, and a transition cap. The transition and free-standing barriers were installed 

on a 3 inches (76 millimeters) thick asphalt pad. The transition utilized a varied spacing of the 

asphalt pin tie-down system to create a transition in stiffness over a series of four barrier 

segments. The asphalt pins used in the design were 11⁄2 inches (38 millimeters) diameter x 381⁄2 

inches (978 millimeters) long ASTM A36 steel pins with 3 inches x 3 inches x 1⁄2-inch

(76 millimeters x 76 millimeters x 13 millimeters) ASTM A36 steel cap plates with a 11⁄2 inches 

(38.1 millimeters) diameter hole in the center. The steel cap was welded on to the pin on both 

the top and bottom surfaces of the plate at a position of 36 inches (914 millimeters) from the 

bottom of the pin to the top of the plate. These pins were installed in the holes on both the front 

and back faces of the four barriers in the transition section of the installation. The first barrier in 

the transition (the one adjacent to the free-standing barrier) had a single pin at the downstream 

end on both the front and back sides. The second barrier had pins installed at the two outermost 

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hole locations on both the front and back faces. The final two barriers had all three pins installed 

on both the front and back faces. 

In order to reduce the potential vehicle snag at the joint between the pinned barriers and the 

rigid parapet, a transition cap and nested thrie beam sections were added. The nested 12-gauge 

thrie beam sections were bolted across both sides of the barrier at the joint between the pinned 

barrier and the rigid parapet. It should be noted that 10-gauge thrie beam can be substituted for 

the nested 12-gauge in actual installations if desired. The thrie beam was bolted to the barriers 

using five 3⁄4-inch (19 millimeters) diameter x 6 inches (152 millimeters) long, Power Fasteners 

Wedge-Bolt Anchors at each end of the beam, as shown in Figure 16. In addition, the middle of 

the thrie section was attached to the pinned barrier with two 3⁄4-inch (19 millimeters) diameter 

Grade 5 bolts and 3⁄4-inch (19 millimeters) diameter RedHead Multi-Set II Drop-in Anchors. A 

wooden spacer block was used to offset the thrie beam from the concrete barrier on the back side 

of the installation. The two bolts on the front face were 1 3⁄4 in. (44 mm) long, while the two on 

the back face were 5 1⁄2 inches (140 millimeters) long. The 12-gauge ASTM A36 steel cap was 6 

1/16 inches (154 millimeters) and 8 1/8 inches (206 millimeters) wide at the top and bottom, 

respectively, with a height of 10 inches (254 millimeters). Four 12-gauge ASTM A36 gussets 

were stitch welded on three sides inside the cap.

The concrete barrier utilized of Iowa’s Concrete Barrier Mix, which was configured with a

minimum 28-day concrete compressive strength of 5,000 psi (34.5 MPa). A minimum concrete

cover varied at different rebar positions within the barrier. A minimum concrete cover of 2 

inches (51 millimeters) was used along the top of the vertical stirrup rebar and at the bottom of 

the longitudinal rebar. Minimum concrete cover of 1 3⁄4 inches (44 millimeters) and 1-inch (25 

millimeters) were used along the sides of the vertical stirrup rebar and at the rebar around the 

anchor bolt block, respectively. All steel reinforcement in the barrier conformed to ASTM A615 

Grade 60 rebar, except for the loop bars which were ASTM A706 Grade 60 rebar. The barrier 

reinforcement details are shown in Figure 11. Barrier reinforcement consisted of three No. 5 and 

two No. 4 longitudinal bars, twelve No.4 bars for the vertical stirrups, and six No. 6 bars for the 

anchor bolt block reinforcement loops. Each of the five longitudinal rebar was 12 feet 2 inches 

(3.71 meters) long. The vertical spacing of the lower, middle, and upper longitudinal bars were 6 

1⁄2 inches (165 millimeters), 14 1⁄2 inches (368 millimeters), and 29 1/8 inches (780 millimeters) 

from the ground to their centers, respectively. The vertical stirrups were 72 inches (1,829 

millimeters) long and were bent into the shape of the barrier and their spacing varied 

longitudinally. The reinforcing steel loops used around the tie-down anchor holes in the barrier 

were 35 inches (889 millimeters) long, were bent into a U-shape, and were used to reinforce the 

anchor bolt area. The barriers used a pin and loop type connection comprised of two sets of 

three rebar loops on each barrier interconnection. Each loop assembly was configured with three 

ASTM A706 Grade 60 No. 6 bars that were bent into a loop shape. The vertical pin used in the 

connection consisted of a 1 1⁄4 inches (32 millimeters) diameter x 28 inches (711 millimeters) 

long round bar comprised of ASTM A36 steel. The pin was held in place using one 2 1⁄2 inches 

wide x 4 inches long x 1⁄2-inch thick (64 millimeters x 102 millimeters x 13 millimeters) ASTM 

A36 steel plate with a 1 3/8 inches (35 millimeters) diameter hole centered on it. The plate was 

welded 2 1⁄2 inches (64 millimeters) below the top of the pin. A gap of 3 5/8 inches (92 

millimeters) between the ends of two consecutive barriers was formed from the result of pulling 

the connection taut. The single-slope permanent concrete barrier was 21 1⁄2 inches (545 

millimeters) and 8 inches (203 millimeters) wide at the base and top, respectively, with an 

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overall height of 42 inches (1,067 millimeters) from the ground to the top of the barrier. The 

single-slope concrete barrier had a overall length of 13 feet 4 inches (4,064 millimeters). The 

concrete used for the barrier consisted of Nebraska 47-BD Mix Type 3, with a minimum 28-day 

concrete compressive strength of 5,000 psi (34.5 MPa). A minimum concrete cover of 2 inches 

(51 millimeters) was used along the entire barrier. All the steel reinforcement in the barrier was 

ASTM A615 Grade 60 rebar. The barrier reinforcement details, which consisted of ten No. 5 

longitudinal bars and fourteen No. 4 and thirteen No. 6 bars for the vertical stirrups are shown in 

Figures 12 and 14. The single-slope barrier employed a 30 inches deep by 36 inches wide (762 

millimeters x 914 millimeters) reinforced concrete footing at its base. The footing was tied to 

the single slope barrier with fourteen No. 6 vertical stirrups that were tied to the No. 4 vertical 

stirrups in the barrier with No. 5 bars. 

Crash Testing

Approach transitions, such as temporary concrete barrier transitions, must satisfy impact 

safety standards in order to be accepted by the Federal Highway Administration (FHWA) for use 

on National Highway Systems (NHS) construction projects or as a replacement for existing 

designs not meeting current safety standards. According to TL-3 of MASH, longitudinal barriers 

must be subjected to two full-scale vehicle crash tests. The two full-scale crash tests are as 

follows: 

1. Test Designation 3-20, consisting of a 2,425-lb (1,100-kg) small car impacting the 

barrier system at a nominal speed and angle of 62.1 mph (100.0 km/h) and 25 

degrees, respectively. 

2. Test Designation 3-21, consisting of a 5,004-lb (2,270-kg) pickup truck impacting 

the barrier system at a nominal speed and angle of 62.1 mph (100 km/h) and 25 

degrees, respectively. 

A rigid, F-shaped bridge rail was successfully impacted by a small car weighing 1,800 lb 

(893 kg) at 60.1 mph (96.7 km/h) and 21.4 degrees according to the American Association of 

State Highway and Transportation Officials (AASHTO) Guide Specifications for Bridge 

Railings. In the same manner, rigid New Jersey safety shape barriers struck by small cars have 

also been shown to meet safety performance standards. In addition, a New Jersey safety shape 

barrier was impacted by a passenger car weighing 2,579 lb (1,170 kg) at 60.8 mph (97.9 km/h) 

and 26.1 degrees according to the TL-3 standards set forth in MASH. Furthermore, temporary 

New Jersey safety shape concrete median barriers have experienced only slight barrier deflection 

when impacted by small cars and behave similar to rigid barriers. The transition was designed to 

prevent any vehicle snag for the small car or truck with no exposed face of barrier when traffic is 

flowing in opposing directions. This asymmetrical placement would only present a safety 

concern if the temporary barrier were used to separate traffic flowing in the same direction, such 

as in a gore area. As such, 2,425-lb (1,100-kg) passenger car test was deemed unnecessary for 

this project.

Two Critical Impact Points (CIP's) needed to be evaluated for the approach transition. The first 

CIP was located adjacent to the point where the transition attaches to the permanent barrier and 

is used to evaluate snag and pocketing near the hazard. The second CIP was located near the 

upstream end of the transition and is used to evaluate the stiffness transition, which can cause 

pocketing and vehicle instability. LS-DYNA was used to determine the CIP (as just upstream of 

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barrier 4) for the second full-scale crash test on the TCB transition, test TCBT-2. For this CIP, 

barrier deflections are expected potentially causing pocketing in the system resulting in 

potentially unstable vehicle behavior or vehicle override of the system. A detailed model of the 

TCB was built and impacted at various locations along the barrier to determine the likely CIP. It 

should be noted that the CIP for the downstream CIP adjacent to permanent barrier was chosen 

as 4.3 feet (1.3 meters) upstream of the permanent barrier. This value is based on guidance for 

CIP values for rigid barriers and temporary concrete barriers provided in Table 2.6 in MASH. It 

represents the distance upstream of a post or joint in a rigid barrier that has increased potential 

for vehicle snag. Due to the high stiffness of the anchored temporary concrete barrier sections 

adjacent to the permanent barrier, it was believed that this CIP location would be sufficient to 

determine the potential for snag on the rigid median barrier.

Test TCBT-1: 

The 5,175-lb (2,347-kg) pickup truck impacted the temporary concrete barrier to permanent 

barrier transition, at a speed of 62.5 mph (100.6 km/h) and at an angle of 24.7 degrees. Test no. 

TCBT-1 was performed to evaluate the transition directly adjacent to the permanent median 

barrier. A summary of the test results and sequential photographs are included in the 

correspondence as an enclosure.

The analysis of the test results for test no. TCBT-1 showed that the temporary concrete barrier to 

permanent concrete barrier transition adequately contained and redirected the 2270P vehicle 

without significant permanent displacement of the barrier. There were no detached elements or 

fragments which neither showed potential for penetrating the occupant compartment nor 

presented undue hazard to other traffic. Deformations or intrusion into the occupant 

compartment that could have caused serious injury did not occur. The test vehicle did not 

penetrate nor ride over the guardrail system and remained upright during and after the collision. 

Vehicle roll, pitch, and yaw angular displacements were noted, but they were deemed acceptable 

because they did not adversely influence occupant risk safety criteria nor cause rollover. After 

impact, the vehicle exited the barrier at an angle of 4.2 degrees and its trajectory did not violate 

the bounds of the exit box. Therefore, test no. TCBT-1 conducted on the temporary concrete 

barrier to permanent barrier concrete transition was determined to be acceptable according to the 

TL-3 safety performance criteria of test designation no. 3-21 found in MASH. 

Test TCBT-2: 

The 5,160-lb (2,341-kg) pickup truck impacted the temporary concrete barrier to permanent 

concrete barrier transition at a speed of 62.2 mph (100.1 km/h) and at an angle of 26.2 degrees. 

Test no. TCBT-2 was performed to evaluate the upstream end of the approach transition. A 

summary of the test results and sequential photographs are included in the correspondence as an 

enclosure.

The analysis of the test results for test no. TCBT-2 showed that the temporary concrete 

barrier to permanent concrete barrier transition adequately contained and redirected the 2270P 

vehicle. There were no detached elements or fragments which neither showed potential for 

penetrating the occupant compartment nor presented undue hazard to other traffic. Deformations 

of, or intrusion into, the occupant compartment that could have caused serious injury did not 

occur. The test vehicle did not penetrate nor ride over the guardrail system and remained upright 

during and after the collision. Vehicle roll, pitch, and yaw angular displacements were noted, 

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but they were deemed acceptable because they did not adversely influence occupant risk safety 

criteria nor cause rollover. After collision, the vehicle’s trajectory revealed minimum intrusion 

into adjacent traffic lanes. The vehicle did not exit the barrier within the exit box yet still exited 

the barrier smoothly. Therefore, test no. TCBT-2 conducted on the temporary concrete barrier to 

permanent concrete barrier transition was determined to be acceptable according to the TL-3 

safety performance criteria of test designation no. 3-21 found in MASH. 

Findings

We concur with the analysis of presented crash test results, including consideration of previous 

successfully conducted Test Designation 3-20, 2,425-lb (1,100-kg) passenger car test in deeming 

this particular crash test unnecessary for this project. Therefore, the system described in the 

requests above and detailed in the enclosed drawings is acceptable for use on the NHS under the 

range of conditions tested, when such use is acceptable to a highway agency. 

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

• This acceptance provides a AASHTO/ARTBA/AGC Task Force 13 designator that should be 

used for the purpose of the creation of a new and/or the update of existing Task Force 13 

drawing for posting on the on-line ‘Guide to Standardized Highway Barrier Hardware’ 

currently referenced in AASHTO ‘Roadside Design Guide’. 

• This acceptance is limited to the crashworthiness characteristics of the systems 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 system 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 system being marketed is 

significantly different from the version that was crash tested, we reserve the right to modify 

or revoke our 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 it will meet the crashworthiness requirements of the FHWA and the AASHTO 

MASH.

• To prevent misunderstanding by others, this letter of acceptance is designated as number 

B-41A and shall not be reproduced except in full. This letter and the test documentation 

upon which it is based are public information. All such letters and documentation may be 

reviewed at our office upon request. 

• This acceptance letter shall not be construed as authorization or consent by the FHWA to use, 

manufacture, or sell any patented system for which the applicant is not the patent holder. 

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• The acceptance letter is limited to the crashworthiness characteristics of the candidate 

system, and the FHWA is neither prepared nor required to become involved in issues 

concerning patent law. Patent issues, if any, are to be resolved by the applicant. 

Sincerely yours, 

Michael S. Griffith

Director, Office of Safety Technologies

Office of Safety 

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