As a method to evaluate delay test quality of test patterns, SDQM (Statistical Delay Quality Model) has been proposed for transition faults. In order to derive better test quality by SDQM, the following two things are important: for each transition fault, (1) to find out the accurate length of the longest sensitizable paths along which the fault is activated and propagated, and (2) to generate a test pattern that detects the fault through as long paths as possible. In this paper, we propose a method to calculate the length of the potentially sensitizable longest path for detection of a transition fault. In addition, we develop a procedure to extract path information that helps high quality transition ATPG. Experimental results show that the proposed method not only derives more accurate SDQL (Statistical Delay Quality Level) but also enhances the test quality of generated test patterns.