ASSESSING THE IMPACT OF RESEARCH - THE CANADIAN EXPERIENCE WITH HEAVY VEHICLE WEIGHTS AND DIMENSIONS

The differences which existed in size and weight regulations within Canada reflected different engineering judgments of the structural capacity of highway infrastructure, the compatibility of large and heavy truck configurations with highway geometrics, and safety concerns for truck performance as weights and/or dimensions change. Research was needed to provide a common technical basis for discussion of harmonization of regulations. The research approached the issues of vehicle weights and dimensions from a "first principles" perspective, focusing in identifying the type and magnitude of impacts that change in truck size and weight parameters would have. Initial studies conducted on bridge capacity concluded that higher capacity existed than previously thought and that variations in the load carrying capacity of different pavement structures used across Canada were likely to be a greater constraining factor. To explore the remaining range of concerns, the largest cooperative highway research program ever undertaken in Canada was developed and launched. Jointly sponsored by thirteen governments and four organizations representing the truck manufacturing and operating industries, a special corporation was established (Canroad Transportation Research Corporation) to assemble the required funding ($3 million), and to organize and steer the research. Pavement strain and deflection data was collected at thirteen sites on the primary highway system across Canada under a common test program comprising a wide range of axle loads and configurations. The test results were analyzed and presented in terms of Equivalent Single Axle Loads (ESAL's for single, tandem and tridem axle groups for loading levels within and beyond the range of typical regulated limits. In support of the discussion of regulatory harmonization, companion studies were also undertaken of the impact of vehicle length, on passing on two-lane highways, and on the economic implications of changes in size and weight scenarios.