ABSTRACT: A series of studies were performed for developing a new test protocol and for characterizing the deformation strength, designated as SD, which was found to have relatively high correlations with wheel tracking and APA results (R2 > 0.8 on the average) at 60°C. In the test, the peak load (P) and vertical deformation (y) at the peak load point were obtained and SD is then calculated by the equation of SD = 0.32P/
( )10 20 2 2+ −y y . Since rutting is known to be induced more severely by slow-moving vehicles, it is necessary to investigate the slower loading speed than 50 mm/min, by which Marshall Stability and indirect tensile strength tests are performed, is needed to be investigated. Therefore, SD test was performed by loading speeds of 10, 30, 50 and 70 mm/min to select optimum loading speed which showed the highest correlation with WT results. From regression analysis results between SD and WT, the 30 mm/min was found to show the highest correlation.