Problems of Designing Roadway Structures

The purpose of roadway structural design is to provide a structural system or pavement which will serve its intended purpose most economically, considering initial cost, maintenance, use of public resources, load use, and usage cost, i.e., lost time and vehicle cost. Many existing pavement design methods do not take this into account and erroneously consider the roadway structure in a much narrower sense, thus fulfilling only a part of the overall design problem. An uncoordinated, piecemeal attack on the problem will not be successful, and, therefore, a systems approach is presented. A more rational and realistic approach toward the understanding of the behavior of pavement materials, including subgrade soils, to provide a better understanding of the complex behavior of pavement materials is described, along with important variables omitted in many present design methods. These include environmental variables, construction variables, maintenance variables, and performance variables. An attempt to summarize and evaluate the current state of the art of the pavement structural problem and to set the stage for work in the future is presented.