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Practical advice on rating roads 27 <br /> Good rural ditch Consider both pavement surface <br /> and driveway drainage and lateral drainage (ditches or <br /> culvert. Culvert <br /> storm sewers). Pavement should be able <br /> end needs .cleaning. to quickly shed water off the surface <br /> . _ into the lateral ditches. Ditches should <br /> RATING: Good ' be large and deep enough to drain the <br /> pavement and remove the surface water <br /> efficiently into adjacent waterways. <br /> - - Look at the roadway- y crown and <br /> check for low surface areas that permit <br /> -"" "- ponding. Paved surfaces should have <br /> approximately a 2% cross slope or <br /> crown across the roadway. This will <br /> _ provide approximately 3" of fall on a <br /> 12' traffic lane. Shoulders should have <br /> a greater slope to improve surface <br /> drainage. <br /> A pavement's ability to carry heavy <br /> High shoulder '' ' '' traffic loads depends on both the <br /> and no ditch lead .� pavement materials (asphalt surfacing <br /> ra <br /> to pavement :• t%r and granular base) and the strength <br /> damage. Needs } �. <br /> _ t of the underlying soils. Most soils lose <br /> mayor ditch . 4,` strength when they are very wet. <br /> improvement <br /> for a short46 ' L . ; <br /> L Therefore, it is important to provide <br /> -`% " <br /> distance. .' .-�'■ � - drainage to the top layer of the <br /> r subgrade supporting the pavement <br /> RATING: Fair structure. <br /> .. t. In rural areas, drainage is provided <br /> most economically by open ditches that <br /> -' - - allow soil moisture to drain laterally. As <br /> a rule of thumb, the bottom of the <br /> • °.� ditch ought to be at least one foot <br /> #'`� �1 - below the base course of the pavement <br /> ' . ' • •; in order to drain the soils. This means <br /> that minimum ditch depth should be <br /> -_"�'i'' •,a - ice, :® about 2 below the center of the <br /> A. <br /> °. .: pavement. Deeper ditches, of course, <br /> No drainage are required to accommodate roadway <br /> leads to failed -° - culverts and maintain the flow line to <br /> pavement. 3= adjacent drainage channels or streams. <br /> You should also check culverts and <br /> RATING: Poor Astorm drain systems. Storm drainage <br /> - systems that are silted in, have a large <br /> accumulation of debris, or are in poor <br /> structural condition will also degrade <br /> -® ' pavement performance. <br /> The T.I.C. publication, Drainage <br /> Manual:Local Road Assessment and <br /> Improvement, describes the elements <br /> of drainage systems, depicts them in <br /> detailed photographs, and explains how <br /> to rate their condition. Copies are <br /> available from the Transportation <br /> T Information Center. <br />