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What is your current recommendation regarding the maximum offset of the MGS behind a 6" AASHTO Type B curb for TL-3 conditions?
I am specifically interested in the case where the top of rail height is 31 inches relative to the gutter elevation.

I am enclosing a copy of a presentation that I gave a few years ago at a TRB AFB20 summer workshop. This presentation was given prior to conducting the failed TL-3 test at the 8 ft offset location. At that time, we had critical lateral locations where we believed one would need to transition from 31" to 37" MGS relative to the road. However, testing would be needed to evaluate these limits.

Originally, the research study was geared toward a performance limits study where we would increment through critical test conditions and locations. However, the project was refocused by the sponsors in the middle of the study where the performance limits portion was replaced with testing at practical locations and then later a lower test level following a failed TL-3 test. As such, we later obtained a successful TL-2 test at the 6-ft lateral offset but still were unable to explore all of the critical locations.

We really are unable to provide much guidance beyond our original MGS testing with the 6" offset at TL-3 and extrapolate some guidance at TL-2 due to the 2270P test. No small car testing was performed with combination curbs and barriers.

An ongoing study funded under NCHRP Project 22-39 is investigating the safe offset and installation height of MGS installed in conjunction with a 6-in. tall, AASHTO Type B curb under MASH TL-3 impact conditions. Additional curb shapes and impact conditions were also considered. The final recommendtions will be published on the NCHRP website. The ongoing research will be updated here:

https://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=4585

At this time, results are not yet publicly available. Nonetheless, two full-scale crash tests were conducted with 37-in. and 32-in. tall MGS systems relative to the roadway at different offsets from a 6-in. tall, AASHTO Type B curb. Both crash tests were determined to be successful according to MASH evaluation criteria. Implementation guidance and limitations on system installations are anticiapted in the final report.