THE DEVELOPMENT OF A PROCEDURE FOR ANALYZING LOAD LIMITS ON LOW-VOLUME ROADS

The Commonwealth of Pennsylvania has 44,000 miles of roads under its jurisdiction, the majority of which have pavements with limited structural capacity. The state has the authority to restrict axle loads on its roads if it believes that those axle loads would result in excessive damage to the pavement structure. The purpose of the research reported herein was to develop rational guidelines for the posting of load limits. To evaluate the effect of axle loads under a variety of conditions, a theoretical analysis was conducted that considered various load magnitudes and configurations for different pavement thicknesses and material properties. It was found that axle configuration (i.e., single-, tandem-, and triple-axle assemblies) did not significantly affect theoretical pavement response, provided that the load per tire and the tire pressure remained the same. After the axle loads were analyzed, a performance model was developed that uses deflection measurements from either the road rater or the Falling Weight Deflectometer to predict pavement performance for a given level of traffic. A microcomputer program was written that incorporates the new procedure and includes a default traffic stream that is typical of low-volume rural roads. The program generates information on the predicted number of years to failure for different load limits, which would enable the user to quantitatively consider the effects of axle-load limits on pavement deterioration. In addition, information useful for determining which axle loads are responsible for pavement damage is provided by the program. An example is given of how the responsibility for pavement damage can be converted to cost responsibility by assessing charges to heavy haulers.