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I work for PennDOT and I’m reaching out about a research report that Midwest conducted back in 2010 using MASH vehicles that it looks like you assisted with. Specifically, I’m reaching out about MwRSF Research Report No. TRP-03-237-10 “PERFORMANCE LIMITS FOR 6-IN. (152-MM) HIGH CURBS PLACED IN ADVANCE OF THE MGS USING MASH VEHICLES PART III: FULL-SCALE CRASH TESTING (TL-2)”. This report is fairly old, but I’m hoping you can help us out with a dilemma we’re having with it.

We are looking to add the information found in this report into our PennDOT standards, however we question the specific phrasing of the report and just want to see if any additional insight could be provided on the thinking found in the report. The section we have questions on is in this paragraph:

We understand the concern over the ground slope, and we understand the concern for making sure the rail height relative to the ground directly below the rail should be no higher than 34”, but we question if making sure the top rail height relative to the top of curb needs to be between 31 and 32 inches, especially if the rail can be laterally placed up to 12’ away from the curb. Our thinking is that the height of the guide rail when the vehicle hits the w-beam is more important than the height relative to the curb.

I know this is a question on a report from 14 years ago, but do you have any additional recollection on the necessity of the 31-32 inch height restriction? We are contemplating if we could restrict the guidance so that the guide rail distance laterally from the curb can be between 4’ to 12’, the maximum cross slope allowed is 4%, and the guide rail height relative to the ground directly beneath it could be between 31” minimum and 34” maximum. We think that could provide enough limitations on the slope to be satisfactory, however we are unsure if that is missing some important factor that the 31-32 inch height relative to curb restriction is providing.

Just for reference, below is a snippet of what we’re considering for implementation of this guidance, with the 2’-7” to 2’-8” measurement and Note 3 possibly being removed:

It’s ok if you are unable to recollect or provide any feedback on our above question, but your feedback is greatly appreciated.

Thanks for reaching out.

We have recently updated the guidance from that report in a follow on study that was completed last year through NCHRP. You can get that report at the link below.

https://nap.nationalacademies.org/catalog/27463/development-of-installation-guidelines-for-midwest-guardrail-system-in-combination-with-roadside-curbs-for-mash-tl-3-applications

See the updated, revised guidance in that report regarding guardrail adjacent to curbs with larger offsets. It is much more detailed than the original effort as we had more modeling and funding.

If you still have questions, let me know.

Thank you, I appreciate the quick response! Yes, that new report is part of the reason we were also looking at this old report from 2010. That new report gives great guidance for TL-3 that we are adding to our standards, but we were hoping to also provide guidance from the older report from 2010 as we thought the TL-2 guidance found there was different enough to still be usable for roadways 40 MPH or under.

Just to pick your brain, do you primarily recommend only using guidance found in the latest report?

NCHRP Report 1089 did look at lower speed curb impacts and the associated effects on vehicle trajectory. The data found that lower speed impacts had minimal affect on the vehicle trajectory and the bumper heights. As such, the recommendations developed for TL-3 in that report are likely valid for TL-2 speeds as well. At least until additional research can be done in that area.

Thanks