MIDWEST STATES POOLED FUND PROGRAM
MGS installed in Mow Strips and Other Un-yielding Pavements
Sponsoring Agency Code
TPF-5(193) Supplement 57
Over the years, it has become desirable to place a longitudinal concrete slab or continuous asphalt
pavement under W-beam guardrail systems in order to reduce the time and costs for mowing operations
around guardrail posts. Likewise, many times guardrail posts must be installed in un-yielding pavements.
Unfortunately, the placement of guardrail posts in pavement restricts energy dissipation by restricting the
posts from rotating through the soil. Thus, guardrail posts have been installed in mow strips where the
concrete or asphalt surfacing does not fill a blocked-out area or â€œleave-outâ€ that surrounds each post.
These leave-outs allow post rotation in the soil and result in acceptable safety performances for standard
Recently, the MGS Bridge Rail was developed and successfully crash tested under the TL-3 MASH
guidelines. This system utilized weak steel posts placed in tubular steel sockets that were side-mounted
to a concrete bridge deck. The energy dissipation mechanism for this system was designed as bending of
the weak posts instead of post rotation through soil. Since the posts are installed in rigid sleeves, MwRSF
believes that the MGS Bridge Rail could be adapted for use in guardrail applications where mow strips
are required. In this situation, it would be unnecessary to provide large leave-outs around the posts of
guardrail systems installed in un-yielding pavements.
Prior research has demonstrated that standard W-beam guardrails may not perform in an acceptable
manner when the guardrail posts are placed directly in an asphalt or concrete pavement that restricts post
rotation. Rail ruptures have been attributed to the loss of energy dissipation in the barrier system when
posts are not allowed to rotate through the soil. The use of leave-outs around the base of the posts
alleviates this issue by allowing post rotations. Many leave-out designs incorporate weak cement or grout
mixes that restrict plant growth but crumble away under impact loads. Therefore, significant effort is
required to reset a post after an impact (i.e., material clean up, soil tamping, post driving, and pouring a
new batch of the weak cement grout).
As noted above, the proposed design for guardrail systems installed in mow strips and other un-yielding
pavements will be a modification of the current MGS Bridge Rail which consists of S3x5.7 steel posts
positioned at half-post spacing (37Â½ in. on center) mounted in sockets attached to the edge of the bridge
deck, as shown in Figure 2. Since the posts are only mounted in sockets, installation and repair of
damaged posts can be completed quickly and with relative ease. The MGS Bridge Rail was successfully
tested to TL-3 criteria of MASH.
The objective of this research effort is to adapt the MGS Bridge Rail system for use in into mow strips and
other pavements. The system may be either blocked or un-blocked.
First, a review will be conducted of the current standards of the Pooled Fund member states and a survey
of the member states to determine their desires concerning guardrail posts installed in mow strips,
concrete, asphalt, and other pavements. From this review, the critical and most common surfaces/slabs
will be identified. Next, bogie testing will be utilized to evaluate the necessity of using a sleeve/socket in
pavement as well as assess pavement damage expected during impacts. MwRSF will conduct the
required MASH full-scale crash tests, test designation nos. 3-10 and 3-11. If the differences between the
bridge rail and mow strip/pavement designs are minimal, then it may be possible to waive test designation
The successful completion of the design and full-scale testing of a MGS mow strip design utilizing weak
posts should provide insight and guidance with respect to the potential performance of other weak post
systems installed in mow strips. This would include weak post W-beam guardrail, cable guardrail, and box
Adapting the MGS bridge rail to be placed in various pavements will allow designers to install the MGS
system in mow strips without requiring leave-outs, breakaway posts, or other additional hardware. It is
anticipated that the new post foundation design will significantly reduce labor and system costs
associated with installation, repair, and maintenance of guardrail installed in mow strips and other
pavements. Insight will also be gained regarding the potential performance of other weak post guardrail
system when installed in mow strips.
Snapshot of Recent Developments
130 Whittier Research Center
2200 Vine Street
Lincoln, Nebraska 68583-0853
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