This paper presents the results of a case study on the translational slide at the Cidu section of Formosan freeway, including its kinematic process and the deposition geometry. Numerical modeling of the slides interaction was carried out using a 3D distinct element program, PFC3D (Itasca, 1999). When the friction coefficient of each particle was about 0.03, the predicted maximum velocity was about 23.6m/sec (about 85km/hr) and the debris reached the other side of Formosan freeway. Simulations showed the three cars and Formosan freeway were buried at 2-4sec (the predicted average velocity was about 10.2m/sec) and the translational slide stopped all motions to form the low fragmentation deposit at 7.5sec.