For the purpose of flexible pavement design, the California Bearing Ratio, or “CBR” value, is used to classify the relative strength of a soil subgrade. The CBR value for a specific material can be determined through laboratory testing. Lower CBR values indicate weaker materials and higher values indicate a material that will provide strong subgrade support. About 85 percent of soils in Kentucky are fine-grained silts and clays and these materials typically range from a CBR value of 1 to 5. Sands, gravels, and rock roadbeds will provide better support and typically have higher CBR values. It is generally assumed that a CBR value of 3 is the lowest CBR value that provides a stable platform for construction traffic. Consider mechanical or chemical stabilization of soils with a CBR value of 1 or 2.