We have used more aggressive slopes for vertical height transitions in the past. Recent testing of the median transition from free-standing TCB to a 42" tall single slope barrier used a sloped, steel cap to transition between the 32" tall PCB segments and the 42" tall single slope barrier.
Before addressing the 27"-32" height transition, we should be clear about the guidance for the 5:1 slope. The 5:1 height transition slope that we tested with the PCB transition used a steel cap to create the vertical transition flare. There is some concern that using concrete to create the 5:1 flare may increase friction and or gouging of vehicle components in the flared region. Thus, the 5:1 is an aggressive approach with some co! ncerns for its use.
For your 27" to 32" transition, the recommendation would still be the 8:1 slope. We would recommend this based on the concerns noted above regarding the difference in the slope materials. In addition, as noted in the first response, we would not want to go to steeper slopes for barrier heights below 32" on the low side due to concerns for increased vehicle exposure to the slope and climb.
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