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I do not have any concerns with using a 12-in. long steel backup plates with the MGS bridge rail system. The original MGS bridge rail system was designed, configured, and successfully crash tested under MASH using 6-in. steel backup plates between the W-beam rail and the S3x5.7 steel posts. Longer steel backup plates would likely reduce the propensity for the flange ends of support posts to contact the backside of the rail after bending and twisting during impact events. As such, we are supportive of using a longer steel backup plate with this system.

On another recent research project involving the 31-in. tall, weak-post, W-beam guardrail system installed in mow strips, we recommended that the 6-in. long backup plates be increased to 12 in. A weblink is provided below to access this research study, report, drawings, and videos. See pages 145 through 148 of the associated research report.

http://mwrsf.unl.edu/reportresult.php?reportId=315&search-textbox=mow%20strip

Based on this recent guardrail research, we also noted within this report that there would be benefit to increasing the length of the backup plate to 12 in. on other similar systems, such as the MGS bridge rail and the MGS post-socketed system adapted to culvert headwalls.

Please let me know if you have any further questions regarding the enclosed information. Thanks!