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You are correct that TL-4 testing of the 10000S single unit truck vehicle during the NCHRP 22-14 project resulted in the truck rolling over the rail in tests at TTI and MwRSF. The increased mass and velocity of the new TL-4 test criteria in MASH have created a more severe test both in terms of impact loading and vehicle stability.

I have attached the TTI report to the email and placed a link to the MwRSF report below.

http://mwrsf.unl.edu/researchhub/files/Report146/TRP-03-177-06.pdf

Subsequent to this work, MwRSF and TTI have done some research into revised barrier heights. MwRSF performed simulation analysis of a vertical shape precast bridge rail design that indicated that 34.5” high vertical shape barriers could potentially meet MASH TL-4. However, this system was never full-scale crash tested to verify those results.

TTI also performed simulation analysis of single-slope barriers that indicated that 36”  high single-slope barriers would meet MASH TL-4. TTI tested the 36” high single-slope barrier with the 10000S vehicle and found that it did safety redirect the SUT vehicle.

http://tti.tamu.edu/documents/9-1002-5.pdf

No testing of increased height safety shape barriers has been performed to date, so we cannot definitively say what the height for those sections would be. However, based on the previously research, it would be recommended that a minimum height of 36” would be reasonable and that the required height may decrease as the barrier geometry becomes more vertical.

No 42” high barriers have been tested to MASH TL-4 to the best of my knowledge. It is highly likely that these barriers would meet MASH in terms of vehicle stability. Keep in mind that it is believed that the MASH TL-4 impact loads have increased as well due to the increased speed and mass. Thus, barrier reinforcement for existing TL-4 barriers may need to be re-evaluated.

Thanks