View Q&A

I’m looking for some clarification on the portion of the system that gates on the trailing end anchorage system. I didn’t think it warranted a formal submittal to the Q&A, but I’m happy to add it if that helps keep the records straight.

In the intended use section of the Standardized Hardware Guide for the system (pg 2), it states

The non-gating, redirective length-of-need of the trailing-end anchorage system is 31’-3” [9525] from the

centerline of the last PDF01 post and includes four PWE06 or PDE02 or PDE20 posts contained in a standard

Midwest Guardrail System (SGR20a-c).

Does that mean that guardrail provided 31’-3” upstream of the first wooden post is considered gating and non-redirective and should not be considered for satisfying the LON? 

The gating and redirective behavior of that system and the recommendations in the report are based on a trailing end installation impact, so the vehicle impact upstream of the end of the guardrail and proceeds toward the end posts. In that case, the end of the LON off the guardrail is further from, the final post in the system as what one is used to on the upstream end. For example the beginning of LON for most end terminals on the upstream end of a guardrail is post no. 2 or 3 in the system depending on the design. The report details some of the derivation of that guidance.

https://mwrsf.unl.edu/researchhub/files/Report279/TRP-03-279-13.pdf

We used the full-scale crash testing and simulation to establish when the vehicle would redirect or gate for the downstream impacts on the trailing terminal. We also provided guidance for hazard placement adjacent to the terminal as shown below. This may provide a better picture of the behavior for you. As you can see, full vehicle redirection was predicted upstream of 31.25’ from the end of the system. That is where the hardware guide guidance come from. To accommodate the gating as you move downstream, we provided guidance on acceptable zones for hazards.

Let me know if this answers your question or if you want to discuss it further. I’d be happy to do so.

The graphic makes all the difference but it now I have one more question.  Is the “End Post” the same as the “last PDF01” called out on the Standardized Guide?

I’m going to try to explain may question

From the graphic you provided, it looks like redirection occurs at Post 8.  Am I interpreting the graphic correctly? 

The Standardized Guide says redirective LON is 31’-3” from the CL of the last PDF01.  That would be Post 6, rather than Post 8.  It goes on to say it would include 4 posts from a standard MGS installation – this could be at Post 6 or 8, depending on whether the two PWE06 posts shown in the elevation view are considered part of the trailing-end or part of standard MGS. 

Should it read 31’-3” from the first PDF01 post (2^nd Post in the graphic)?  But that would be Post 7.  [Side note:  the description of the working width recommendations from the last PDF01 seem to line up with the graphic].

In response to your question. The 2270P vehicle did redirect for an impact at post no. 6 or 31.25’ upstream of the first post in the system. The trajectory in the plot below does not show the full vehicle response. Note that the deflection is greater than a typical redirection. See the summary sheet below with the trajectory plotted.

As such, the redirective LON is 31.25’ upstream of the end post or at post no. 6. That would include two BCT posts and four standard MGS posts.

Let me know if that clears things up or if you want to discuss further.