The construction of Underpass at Kentungan intersection is one of a solution to improve the road network performance on the D.I. Yogyakarta and reduce the frequent congestion and queue length . Therefore, to determine the magnitude of the impact of traffic caused by the development and efforts to deal with the problems that occur, a Traffic Impact Analysis study is needed. This study aims evaluated the performance of Kentungan intersection from the construction of the underpass, especially during construction. Data are collected through surveys of road invtentory, traffic volume, spot speed, intersection geometrics, queue length and cycle time of phase of Kentungan intersection. The analysis of traffic performance refers to Manual Kapasitas Jalan Indonesia (MKJI) 1997. The results of the study showed that at the construction stage of Kentungan intersection had a total traffic volume is 3585 pcu / hour with a degree of saturation of 0.707, an average delay of the intersection is 40.92 and the level of service is E; for the operational stage of underpass the results obtained are the level of services included in category C. The solution for handling during construction is to divert traffic flow at the Kentungan intersection especially for heavy vehicles and alternatively during operation using the change in APILL cycle time from north and south.