Methodology for Load-Zoning Pavements (0-2123-S)

Texas has approximately 17,500 miles of load-zoned pavements, comprising more than 20 percent of the number of centerline miles on the state-maintained system. These pavements are primarily low-volume farm-to-market roads constructed in the 1950s at a time when legal load limits were lower than they are now. Like most governments, Texas does not have the money to upgrade all existing load-zoned pavements to accommodate present truck traffic, nor is this justifiable for many of these pavements because of the continuing low traffic volumes. To do so would divert funds from higher-priority highway and bridge improvement projects. Most load-zoned roads in Texas are still posted with a gross vehicle weight (GVW) limit of 58,420 lb, corresponding to the legal load limit at the time these roads were designed and built. Since the load from a vehicle is transmitted to the pavement through its axles, establishing load limits based on axle weight and axle configuration is a more rational approach than the one presently used . Recognizing the need for a better methodology of load-zoning pavements, the Texas Department of Transportation (TxDOT) funded a project to develop a procedure for evaluating load restrictions on the basis of axle load and axle configuration. Research efforts conducted at the Texas Transportation Institute (TTI) led to the development of the Program for Load-Zoning Analysis (PLZA) that pavement engineers may use to evaluate the need for load restrictions and to determine, as appropriate, the single and tandem axle load limits based on a user-prescribed reliability level.