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HDR in Chicago, IL had questions regarding the proper connection between the Iowa approach guardrail transition and various concrete parapets.

I have reviewed the research and development effort regarding the approach guardrail transition system for safety shape parapets. The original study was funded by the Midwest State's Pooled Fund Program and dated May 15, 1998. The report no. is TRP-03-68-98. I am attaching a link for you to download this report. In the study, it is apparent that five 7/8-in. diameter, ASTM A325 bolts were used to attach the thrie beam end shoe to the parapet with the use of a special steel connector plate with a sloped end to mitigate concerns for vehicle snag. The special steel connector plate was also used to keep the thrie beam vertical and not twisted when attached to the parapet. The final design was crash tested and evaluated with both wood and steel post options and using the NCHRP Report No. 350 impact safety standards.

The file 'TRP-03-69-98.PDF' (7.1 MB) is available for download at

for the next 7 days.

It will be removed after Wednesday, October  7, 2009.

Later, MwRSF performed an additional crash test on the steel post option when completing NCHRP Project No. 22-14(2) which led to the new Manual for Assessing Safety Hardware (MASH) guidelines. One 2270-kg pickup truck crash test was successfully performed on the same design as noted above. The report no. is TRP-03-175-06 and dated October 12, 2006. I have attached a link for you to download the noted report. Once again, five 7/8-in. diameter, ASTM A325 bolts were used to attach the thrie beam end shoe to the parapet with the use of a special steel connector plate with a sloped end to mitigate concerns for vehicle snag.

The file 'TRP-03-175-06.pdf' (9.0 MB) is available for download at

for the next 7 days.

It will be removed after Wednesday, October  7, 2009.

In the pdf file that you had provided, it was apparent that the thrie beam end shoe was blocked out off of the parapet with a wood shim block. You also noted that the end shoe was attached using five ¾-in. diameter, ASTM A307 bolts. Both the shim block and bolt hardware differ from the crash tested system details.

At this time, I am unaware of any successful crash testing on thrie beam approach guardrail transitions where the thrie beam end shoe has been twisted to match the slope of the upper parapet region. As such, it is my opinion that the existing crashworthy design details should be utilized when installing this transition system. For trailing end locations, the wood shim block would potentially lead to vehicle snag on the raised end shoe. Thus, the wood shim block should be replaced with the special, sloped, steel connector plate to mitigate snag concerns and to comply with the design that received FHWA acceptance. Second, the use of a special steel connector plate can cause some of the connection bolts to be subjected to combined loading " shear and bending. With that in mind, the five bolts were upgraded in the crash tested design and utilized 7/8-in. diameter, ASTM A325 hardware. In the absence of any other test results, it is my opinion that the connection hardware should comply with that utilized in the crash testing program.

You are correct. The steel connector plate would not be needed when the transition is attached to a vertical concrete parapet. However, the 4-in. lip curb was required by FHWA as it was included in the testing program.

The attachment bolts are to be 7/8-in. diameter and ASTM A325 bolts or equivalent. Also, the steel connector plate is required for NJ, F, and single slope barriers. We have developed one for NJ and SS shapes.

Slight modification may be needed for F shapes. The Texas A&M Transportation Institute evaluated the design of an approach guardrail transition with a twisted thrie end connection to sloped face of a concrete buttress and a curb in the AGT region. The results of MASH Test Designation 3-21 in test no. 469469-5 were determined to be successful. More information may be found here:

https://www.roadsidepooledfund.org/wp-content/uploads/2020/02/0-6946-R3.pdf