Systems Approach to Flexible Pavement Design and Management

A project is reported which resulted in the improvement of the computer program, SAMP5, to an operational program, SAMP6, which provides a basis for selecting flexible pavement design and management strategies with the lowest predicted total cost over a prescribed analysis period when considering such cost elements as initial construction, routine maintenance, periodic rehabilitation, interest on investment, salvage value, and roadway user costs. The SAMP6 program uses the AASHTO Interim Guides as its structural subsystem and the predicted decreases in serviceability with time and traffic as developed at the AASHO Road Test. The SAMP6 is capable of considering all aspects of the systems approach to pavement design and management except those of the cost of seal coats and the cost of skidding accidents. The program requires 12 classes of input variables: program control and miscellaneous variables, environmental serviceability, traffic and reliability; constraint; traffic delay; maintenance; cross-section, cost-model, shoulder; track coat, prime coat, bituminous materials; wearing surface; overlay; pavement material; and shoulder material variables. The output of the SAMP6 program is provided in three parts: Summary of the input data; summary of the best design strategy for each material and layer combination; and a summary of the 80 best design strategies in order of increasing total cost per square yard of traffic lane. The results are given of a limited sensitivity analysis conducted to provide an indication of the influence of the individual variables on the output. As an illustration of the application of SAMP6, a comparison is described of the economics of staged construction and planned rehabilitation versus the "no-overlay", or a strong initial construction approach. Another illustration involved the effect of fluctuating material costs on optimum design.