FACTORIAL STUDY OF RELATIONS BETWEEN PAVEMENT COST AND LEGAL AXLE LOADS

Results are presented of a study conducted to estimate lifetime costs for flexible pavements as a function of legal axle-load limits by using an improved version of the VESY IIM computer program. VESYS IIM was modified to include capabilities for (a) seasonal characterizations of pavement materials, (b) a discretized representation of axle-load distribution, and (c) predictions of low-temperature cracking. A literature survey and a laboratory testing program were combined to produce definitions of the variations in permanent deformation parameters as important material characteristics vary seasonally with the environment. These data and other information and experience were applied to produce input data that would yield realistic performance predictions. A factorial of 64 solutions was obtained by using the input data and the improved version of VESYS IIM to study the effects of truck traffic for four levels of legal axle-load limits, two levels of traffic, two levels of pavement-section thickness, and four environmental zones. When failures were predicted, an overlay was applied and a new solution obtained until a pavement life of at least 20 years was attained. Initial and overlay costs were estimated, and these costs, for 20 years of pavement service, were related to legal axle-load limits. Estimated costs for 20 years of pavement service were considerably increased by increasing legal axle loads, and estimated cost increases were more severe for the northern than for the southern environmental zones of the United States. (Author)