We are in the process of finalizing our MASH MGS standard details and would like a quick review for the content.
One of the remaining details is the minimum distance either behind the post or from the face of rail to a hazard. Do you have a detail of the distance and how it is measured for the MASH testing or a description similar to page 225 of the NCHRP 350 report?
Thanks
The following text is located in MASH with respect to the deflections and working width. They may help serve as basic definitions for you.
“Test article deflections—Report the permanent and dynamic deflections of the test article plus the working width during impact. These measurements normally apply to longitudinal barriers, terminals, crash cushions, and TMAs. Permanent deflection is the residual lateral displacement of the test article remaining after the impact. Dynamic deflection is the maximum lateral displacement of the test article on the traffic side that occurs during the impact. The working width is the maximum dynamic lateral position of any major part of the system or vehicle. These measurements are all relative to the pre-impact traffic face of the test article. For the working width, the height of the maximum working width should also be documented and reported.”
“working width—The distance between the traffic face of the test article before the impact and the maximum lateral position of any major part of the system or vehicle after the impact”
Working width would define the distance from the face of the rail to the hazard.
We have fielded questions regarding the variation of the MGS dynamic deflection and working width in the past for several states. Related to that, we have compiled charts of the working width and deflections for the standard system. These can be seen below. A chart with similar values is located in the Roadside Design Guide.
Table 1. Guardrail Testing under Test Designation 3-11.
Testing Agency
Test Number
Testing Criteria
Dynamic Deflection
in. (mm)
Working Width
MwRSF
NPG-4
350
43.1 (1,094)
49.6 (1,260)
2214MG-1
MASH
57.0 (1,447)
57.4 (1,457)
2214MG-2
43.9 (1,114)
48.6 (1,234)
MGSMIN-1
42.2 (1,072)
48.8 (1,240)
MGSDF-1*
60.2 (1,529)
60.3 (1,530)
MGSPP-1*
37.6 (956)
MGSWP-1*
46.3 (1,176)
58.4 (1,483)
MGSSYP-1*
40.0 (1,016)
53.8 (1,367)
MGSRF-1*
55.8 (1,417)
57.4 (1,458)
MGSNB-1**
34.1 (867)
43.2 (1,097)
TTI
220570-2**
40.9 (1,040)
44.0 (1,119)
SwRI
GMS-1**
35.0 (890)
NA
400001-TGS1**
38.4 (975)
40.8 (1,036)
Holmes Solutions
057073112**
41.3 (1,050)
*Guardrail with alternate posts and/or blockouts.
**Guardrail with no blockouts.
Table 2. Guardrail Testing under Test Designation 3-10.
NPG-1
17.4 (441)
40.3 (1,022)
2214MG-3
35.9 (913)
48.3 (1,227)
MGSSYP-2*
22.2 (564)
39.7 (1,008)
MGSRF-3*
MGSNB-2**
29.1 (740)
34.5 (877)
The deflections and working widths listed for the MGS do fluctuate, even for the steel post version with standard 6’-3” post spacing. This fluctuation in the working widths is a reflection of several factors.
While it is clear that deflection and working width data taken from full-scale crash tests can vary for several reasons, we have still not answered the question regarding what values you need to consider for your installations. Our advice here would be to review the available data from the crash tests of most similar systems and error on the side of being conservative. For example, if you have an MGS system installed on a 2:1 slope, then we would recommend using the working width guidance from the full-scale crash test of the 2:1 slope. For standard, steel post installations, we may suggest considering a working width of 60 in. The 60-in. working width corresponds with the upper end of the values observed in the full-scale testing and also allows for some tolerance if the soil for your real world installations in not as stiff as the soil currently specified in MASH. For the wood post versions of the standard MGS system, we would recommend that you refer to the crash tests of the specific wood post system and use those working widths if they are increased over the 60-in. For the ½ post and ¼; post spacing versions of the system, we would recommend using the tested working widths listed in the RDG.
Let me know if this addresses your concerns and if you have further questions.
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