Truck size and weight issues have been at the center of highway cost allocation studies, pavement thickness and geometry design standards for separate jurisdictions, and vehicle configuration regulation. Policy makers have proposed longer trucks with increased axle weights as a way to improve industry efficiency, thicker pavements to reduce road system maintenance costs, and alternate pavement designs with modified taxing and licensing structures to encourage a more effective national transportation infrastructure. The issue of an appropriate state response to Federally mandated acceptance of Longer Commercial Vehicles has been delayed, but states such as Iowa must examine the need for modified design specifications for designated commercial highway networks that may someday have to accommodate heavier and longer vehicles.

The relationships between axle weight and pavement damage are traditionally based on the data collected in the AASHO road tests nearly forty years ago. The pavement designs and vehicle configurations evaluated were far different from those in use today. The Strategic Highway Research Project (SHRP) collected additional data on accumulated pavement damage and the relationship to estimated Equivalent Single Axle Loads (ESALs) over the life of the pavement. The problem is by nature very multi-dimensional, involving very specific aspects of pavement design and maintenance, quality control in the initial earthwork and paving that defines the geometry of the roadbed, and maintenance of pavement serviceability. The vehicle mix using the system coupled with enforcement of vehicle configuration and axle weight regulations, will determine the eventual service life of the high facility.

This study provides information about the issues involved through models of vehicle dynamic loads and their effect on selected pavement structures. The model structure allows estimates of the cracking and failure of rigid pavement slabs and joints as a result of repeated applications of the dynamic loads estimated for specific gross vehicle loads and tractor-trailer configurations. Different pavement thickness designs are evaluated in terms of their time to full depth cracking and slab failure. A summary of studies related to safety and vehicle performance details some critical issues facing highway engineers and transportation planners.

Research for this project was carried out at the University of Iowa Public Policy Center. Funding was provided by the U.S. Department of Transportation, University Transportation Centers Program. This program was created by Congress in 1987 to "contribute to the solution of important regional and national transportation problems." Following a national competition, the program established university-based centers in each of the ten federal regions. The Midwest Transportation Center that funded this project is one of those centers; it is a consortium that includes Iowa State University and the University of Iowa. Matching funds were provided by the Iowa Department of Transportation, which also provided some of the data needed to complete this project.

The research team has benefited greatly from its collaboration with a five-member project advisory committee. This committee helped to focus the issues to be addressed, and its members shared their insights throughout the research process.

$6.95, 109 pp., 89 figures, tape binding