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I think the best treatment for the area would be to added a short concrete parapet section adjacent to the bridge rail on the other side of the joint. This was previously mentioned by Victor Veliz in the email string attached, and I believe you had noted that IL-DOT currently installs a 15-ft long parapet adjacent to joints for new construction.  I will go one step further and recommend using the standardized buttress that shape that was recently developed for thrie beam transitions.  The length of the buttress may be only 5-7 ft and the downstream end of the buttress could be made to match the geometry of the existing bridge rail.  The thrie beam would attach to the new buttress and the entire system would be crashworthy.  I have attached a TRB paper that was written on this standardized transition buttress (the report has not yet been completed).  If you are interested in using the buttress, I can work with you on developing the details for this application.

I don’t really understand the design being recommended that incorporates a strong post connection to the abutment similar to your standard 630101-10.  I pulled that detail from IL-DOT website, and this attachment design is for use on culverts or other locations where the embedment depth for the post is not attainable. Maybe I misunderstood the installation issues you are having, but I don’t know how this helps.  If you need to attach a transition post using this design, I don’t think it would hurt the performance of the transition.  However, this attachment does not address the issue of running guardrail across an expansion/contraction joint, which is not recommended.

Parts of the email state that the joints are being “removed/replaced.”  If the joint is being removed altogether, then there is no issue with spanning guardrail across the old joint location.  If the joint is repaired/replaced and is still expected to allow movement, I would not recommend spanning rail across the joint.  Even if the terminal connector (or end shoe) were slotted to allow some movement without loading the thrie beam, this could also allow the thrie beam to deflect significantly prior to building any axial tension and forming the membrane action required to redirect vehicles with guardrail systems.  Thus, slots may result in increased system deflections and snag issues on the concrete bridge rail.

Let me know what else I can do to help