This paper presents traffic conflict analysis and proposes a new conflict indicator for developing ITSassisted traffic safety system under congested and high-speed traffic environment. The conflict analysis is carried out using a Vehicle Tracking System using a digital VCR developed by the authors. After reviewing the previous works of the traffic conflict analysis, the significance of the traffic conflict analysis is stated using hazard and risk concept that associates traffic conflicts with traffic accident occurrences. Next, the conventional traffic conflict indicators, such as TTC, approximate-TTC, PET, etc. are demonstrated. The characteristics of these conflict indicators are discussed. Then, based on these discussions, the requirements for desired conflict indicators for truly appropriate and effective to alert drivers under congested and highspeed traffic are discussed for ITS-assisted safety system. Finally, PTTC indicator as a new conflict indicator for congested traffic is proposed and demonstrated for an actual traffic conflict.