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We have a guard fence transition to a bridge that was recently hit.  This will be repaired per our maintenance policy.

My question is:

    1.    Can we use double blockouts in the portion where the curb is in front of the guard fence for the full length of the guard fence to bridge rail transition section?  How many posts can have more than one blockout and is there a limit, i.e. some may want to use three blocks on several posts.  I am looking into the height of the bridge rail to see if we can get thrie beam on it.

I have reviewed the photos you sent and I believe we can retrofit your installation to improve it significantly. I have attached a schematic of our proposed modifications. We are basically proposing that you blockout the existing system using 24" deep spacer blocks (basically three standard 8" deep blocks in series). We have used 16" blocks on several systems in the past with no problems and we believe that 24" of spacer block is okay as well. We are also recommending that you replace the first 12'-6" section of w-beam with nested 12-gauge thrie beam. Then a W-thrie transition section would be placed between the nested thrie and the standard w-beam. This layout would make you installation very similar to the Iowa transition developed by the Pooled Fund and would increase the safety of the installation greatly. After the W-thrie transition section, the spacer blocks could be reduced incrementally to taper the w-beam to meet the existing installation.

MwRSF has full-scale crash tested approach guardrail transitions (AGTs) with a standard buttress, with and without curbs, and with an asymmetrical W-to-thrie transition. The newer designs utilize MGS, instead of traditional G4(1S) W-beam. In general, updating hardware to reflect the current best-available guidance is recommended. Nonetheless, the use of additional blockouts in system design and implementing nested rail adjacent to the transition is still an effective strategy for improving crashworthiness of AGTs.

https://mwrsf.unl.edu/reportResult.php?reportId=359

https://mwrsf.unl.edu/reportResult.php?reportId=415

https://mwrsf.unl.edu/reportResult.php?reportId=295

https://mwrsf.unl.edu/reportResult.php?reportId=453