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The following recommendations apply ONLY to the MGS trailing-end anchorage system.  Upstream anchorages/terminals are designed with specific post configurations throughout the terminal's stroke length.  Thus, the upstream end of guardrail installations (within stroke length or terminal length specified by manufacturer) should be installed as-tested or as-recommended by the manufacture.

For the non-proprietary, trailing-end MGS anchorage, a reduced post spacing can be placed closer to the end of the system.  However, there are still concerns about the ridedown accelerations for small car impacts if the reduced post spacing is placed too close to the anchorage. The small car test on the downstream anchorage, test WIDA-2 contained within report TRP-03-279-13, resulted in significant snag on the cable anchorage assembly. If the guardrail was made stiffer in this area, the decelerations may exceed MASH ORA limits.  The critical impact point for the small car was located between post 2 and post 3, or about 9.5 ft upstream from the end post.  In order to avoid changing the stiffness in this area of the anchorage, and without conducting further evaluation of the system with reduced post spacing, we recommend beginning reduced post spacings beyond post 4, or 18.75 ft from the end post. This distance represents a distance nearly twice as far from the end post as the CIP for the small car on this system, and thus, shouldn't affect the performance of the trailing-end anchorage with respect to 1100C impacts. 

Note, the CIP for the 2270P pickup truck was 31.25 ft upstream from the end post. Installing reduced post spacing within this region will increase stiffness and reduce deflections.  However, there are no known crashworthiness concerns with placing reduced post spacing beginning at post 4 as described above.  The end of length-of-need would likely be shifted slightly downstream, and the working width envelopes would likely be decreased for impacts within the reduced post spacing region. However, without conducting further analysis, the corresponding values described in report TRP-03-279-13 can still be conservatively used.

Similarly. for trailing end installations utilizing standard 12.5-ft or 25-ft long guardrail segments with the end of the rail located at post 1 (no rail extending beyond the end post), the span between posts 4 and 5 from the downstream end may be reduced to 37.5 in. (half-post spacing) to move the splices away from post locations and to mid-span locations, as desired for standard MGS installations.  Thus, the guardrail upstream from post 5 from the end would be standard MGS with 75" post spacing and guardrail splices located at mid-span.