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How close is too close for an approach transition post?

Vonsistent with our discussion earlier in week.  I have a contractor that is offering concern on installing Thrie beam transition adjacent to underground vault and are seeking copy of email concurrence on project direction.  Depiction attached and below. 

Bottom roughly 12” of 4 posts will be 6” +/- off of adjacent vault.  Posts will not be against vault.  Posts will be able to rotate.   Posted speed is 40 MPH.

Thrie Beam is being installed at slight angle at show connection at parapet on bridge.  We are not proposing bending the nested thrie beam or the nested W rail.  It is proposed to be installed on tangent.  We are not proposing to split any offset blocks.

Appreciate concurrence on this installation.

For the installation shown, it appears that only the lowest 12” of the post will have the potential to interact with the buried structure. When a post is loaded and displaced in soil, the post tends to rotate about a point approximately 2/3 of the embedment depth below the ground. The upper section of the embedded post rotates backwards when loaded and the lower portion below the rotation point moves forwards. In the case you have shown, we would assume that the post rotates about a point around 13” below grade. As such, the potential interaction of the post with the structure is minimal and should not post a performance issue within the AGT.