THE STATE-OF-THE-PRACTICE IN MARYLAND--PART I

This drainage presentation denoting the practices of the Maryland State Highway Administration (MSHA) is divided into two parts: the drainage systems that are used by the MSHA for both rigid and for flexible pavements, and the drainage components comprising several alternative drainage systems for both rigid and flexible pavements. Of major significance to surface drainage and pavement integrity is the composition of the pavement surface course. Four types of subsurface drainage systems are used by the MSHA: extended granular subgrades or subbases, continuous longitudinal pipe underdrain, subgrade drains, and conventional pipe underdrain. The selection of one or more of these drainage systems is dependent on the type of pavement and type of shoulder that is decided for a specific project. This pavement selection is based on an economic analysis. The nature of the highway facility and the justifiable funds that can be expended for the drainage system also become weighted factors in the selection of the proper system. The concept of all-bituminous black base on a prepared subgrade has not been totally accepted as the answer to the elimination of trapped water in a pavement structure. Maryland has developed a policy of sedimentation control during construction wherein both temporary and permanent installations are constructed. These water flow controls have proven to be a significant supplement to the designated drainage system--both to limit water entrance to the pavement and to effect water discharge.