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We would like to update the approach guardrail to MGS at these existing bridge ends.  Would we still be able to install our standard AGT given the height of the existing curbs?  If not, would you recommend grinding the curb down, or should we investigate the use of a w-beam (rather than thrie-beam) AGT here?

Considering the existing concrete curb measures up to 12 in. tall, we would recommend that you remove it and replace it with the standard 4 in. wedge curb. Then, it would be appropriate to implement the modified thrie beam approach guardrail transition with new MGS stiffness transition. For now, we are also guiding the State DOTs to end the concrete curb on the thrie beam end of the asymmetrical section in order to reduce concerns for vehicle snag under the sloped rail. Please let me know if you have any more questions or comments on this matter. Thanks!

We can remove the 12-inch curb on the approach to the bridge and replace it with a 4-inch curb.  However, the 12-inch curb will still be present on the bridge.  Should we transition the 4-inch curb up to 12 inches say, in the last foot prior to the bridge?  Or is there another method we should employ to mitigate the snagging potential?  Or is snagging here not a concern?

I think there are two options.

First, you might consider tapering the brush curb back toward the face of the vertical wall as long as rebar does not get in the wall of the grinding. Then, there would be no curb at the end of the parapet but instead a vertical face. You may also need to taper the end of the wall to reduce concerns for wheel snag there. We prepared draft CAD details for this which are contained in a FHWA approval letter associated with the original Iowa transition but directed to TxDOT. Let me know if you need these details.

Second, you might consider adding a 1-2 ft long RC buttress and foundation which eliminates the curb in front of the vertical parapet and has a tapered end to reduce wheel snag concerns, similar to above.

Can you accommodate any of these ideas?