Mow Strip Design and Practices - WisDOT Research

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AASHTO Technology Implementation GroupCable median barriers are a focus technology for AASHTO’s Technology Implementation Group. Resources relatedto barrier design, roadway design and maintenance are available athttp://tig.transportation.org/?siteid=57&pageid=2197.National Cooperative Highway Research ProgramNCHRP has two projects in progress related to standard practice for cable barrier design, construction and use.Project 20-07, Task 210, “Guidelines for the Selection of Cable Barrier Systems”http://www.trb.org/TRBNet/ProjectDisplay.asp?ProjectID=1226Principal investigator Dean Alberson of the Texas Transportation Institute provided us with the draft final report forthis project, which we are providing as a separate document as it has not yet been approved for public distribution.The project’s purpose was to “develop preliminary guidelines for the selection and use of cable barrier systemsbased on a state-of-the practice review of cable barrier installations.” NCHRP’s administrative contact for this studyis Charles Niessner.The report references issues related to mow strips, including common practices and design issues:Extent of useBased on the investigators’ survey of state DOTs: “When asked if the participating states used mow stripsunderneath the cable barriers, 44% replied positively (27 responses were received). Some of these states alwaysuse mow strips with cable barriers, while others have used them intermittently. One of the states indicated thateven though they have experimented with using mow strips in the past, their current preference is not to usethem. One of the states indicated that the decision to use mow strips is left to the designer and another indicatedusing mow strips when the budget allowed. Most states use asphalt mow strips. One of the states indicated usingconcrete mow strips and another indicated using coarse aggregate” (page 39 of the PDF).Typical geometry“Participants were also asked about the typical width and thickness of the mow strip used in their states. Fiveout of seven states that responded indicated using a 4-ft-wide strip. One state indicated using 6-ft-wide stripsand another indicated using 2- to 4-ft-wide mow strips. Two of the six responding states indicated using 2-inchthickmow strips and the remaining four indicated using 4-inch-thick mow strips” (page 39 of the PDF).Use with socketed posts“A number of states have elected to install socketed systems that facilitate repair of the system, and whencoupled with a mow strip, they simplify mowing operations. Continuous mow strips have also eliminated socketand anchor movements in weaker soil conditions” (page 12 of the PDF). The report details the socketed design(pages 61-62) and compares state use of socketed versus driven posts (page 37).Project 22-25, “Development of Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems”http://www.trb.org/TRBNet/ProjectDisplay.asp?ProjectID=1640This project will address the “need to formulate guidelines and standardized practices for cable barrier systems.”This project is a more comprehensive follow-up to Project 20-07, Task 210 (above), and will address design,construction and performance issues in detail. The status of this project is listed as pending on the TRB Web site.NCHRP administrative contact Charles Niessner told us that a contractor has not yet been selected.Contacts:Charles Niessner, NCHRP Senior Program Officer, (202) 334-1431, cniessner@nas.edu.Dean Alberson, TTI Crashworthy Structures Program, (979) 458-3874, d-alberson@tamu.edu.2
State Experiences and PracticesThe information below includes details collected from several state DOT representatives. In addition, Illinois DOT’sHigh Tension Cable Median Barrier: A Scanning Tour Report(http://tig.transportation.org/sites/aashtotig/docs/High%20Tension%20Cable%20Median%20Barrier%20-%20Scanning%20Tour%20Report.pdf) describes installation experiences in Ohio, Oklahoma and Texas; we provideexcerpts of these descriptions by state below.GeorgiaA contract addendum for a highway project in Georgia’s Franklin and Hart counties contains specifications for apaving strip under the cable barrier. It provides two alternatives: a 6-foot-wide Superpave-compliant asphalt strip ora 4-foot-wide Class A concrete strip. Detailed drawings are attached as Appendix A to this synthesis report (pages 4and 5 of the file at http://tomcat2.dot.state.ga.us/ContractsAdministration/uploads/c002a01-061020.pdf).OhioOhio DOT Standards Engineer Dean Focke said that for a recent Ohio DOT cable barrier project, a plan sheetdetailed the construction of the paved mow strip, referred to as a “paved berm.” This plan sheet is attached asAppendix B to this synthesis report.Contact: Dean Focke, dean.focke@dot.state.oh.usAccording to the Illinois scan tour report (see pages 17-18 of the PDF), 3 miles of cable barrier system werecompleted in Ohio in October 2004: “The barrier was placed at the edge of the paved shoulder on an asphalt mowstrip. Posts were installed in sockets with concrete foundations and spaced 10 feet with a design deflection of 7.9feet. … Mowing and snow plowing are concerns that are recommended to be addressed at the design stage.”TexasFact Sheet: Cable Median Barriers, March 2007http://www.transportation.org/sites/aashtotig/docs/Texas%20-%20CMB%20Background%20and%20Facts%20%283-2007%29.pdfIn this fact sheet, Texas DOT reports that “Most districts are also placing mow strips with the cable barrier systemsfor maintenance considerations.”Memorandum: Cable Barrier Systems, June 2006http://www.transportation.org/sites/aashtotig/docs/Texas%20Cable%20Barrier%20Systems%20Memo%20%282006%29.pdfIn this memo on cable barrier systems, TxDOT notes that “future mowing requirements” are a factor to considerwhen selecting whether to use a cable barrier (see page 1 of the PDF).Further, “the Maintenance Division encourages the use of mow strips to reduce future hand mowing or herbicideoperations. Distance between the edge of the travel lane and the cable barrier should consider mower widths. Thesame consideration apply to distances between the cable barrier and other objects such as the guardrail, bridgecolumns, and end treatments” (page 5 of the PDF).“Power Curber 5700-B Accelerates Median Mow Strip Installation,” Texas Contractor, January 2007http://www.acppubs.com/article/CA6403748.htmlThis article describes the installation of 45 miles of mow strip for a cable barrier system in Texas. The process isdescribed in detail: “In the slipform application, the holes for the posts are bored first at marked locations on theinterstate. Then, the mow strip is slipformed, with concrete filling the holes. … The posts are then inserted into thewet concrete and the wire cable is installed for the Safe Roads, LLC U.S. high-tension cable system.”In addition, the Illinois scan tour report describes an installation in Texas: a 4-foot-wide by 3-inch-thick asphaltmow strip designed “to help reduce cable barrier maintenance. It is believed that the strip also makes cable barriermore noticeable for first responders, who may suddenly need to cross the median in the case of an emergencysituation…. It was recommended to control the water level at the mow strip to avoid premature asphalt deteriorationand additional maintenance. Even though cable barrier doesn’t need to be mowed because of the asphalt strip,TxDOT protects the installation from damages caused by mowing contractors by charging them $100 per postdamaged” (page 27 of the PDF).3
Page 4 and 5: A 2004 letting schedule for Texas
Page 8 and 9: Appendix B: Ohio DOT cable barrier
Page 10 and 11: Appendix D: Weed Mat specifications

Mow Strip Design and Practices - WisDOT Research

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