A vertical taper of 5:1 was used with a steel cap to mitigate vehicle snag on a barrier end above PCBs as they connected to a taller permanent barrier. For vehicle sheet metal to steel cap contact, vehicle performance was acceptable in that crash test.
https://mwrsf.unl.edu/researchhub/files/Report54/TRP-03-208-10.pdf
If vehicle contact to a concrete taper is similar enough, then one may argue to go that route. I do believe the friction and gouging are higher in the later scenario. Although it may be possible to use 5:1, a more conservative route would be to use the 6:1 that Scott had incorporated into the standardized buttress, which demonstrated acceptable crashworthiness in the 2270P transition test.
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