National Institute for Human Science and Biomedical Engineering of AIST and HQL(Research Institute of Human Engineering for Quality of Life ) have conducted a research project with Toyota Central R & D Labs Inc., Mazda Motor Corp, Nissan Motor Co. Ltd and Yokogawa Electric Corp. to develop technologies for realizing Personal Fitting Driving Assistance Systems. In order to understand how people drive a car in a real road environment, quantitative behavioral data of a hundred drivers were collected using equipped vehicles. The collected data were stored in a workstation to establish a Car Driving Behavior Database for convenient use of the data. We can clarify individual driving behavior quantitatively by analyzing the data in the database. Focusing on deceleration maneuver when approaching to an intersection with a stop sign, we identified range of the normal driving behavior from a large amount of the behavioral data obtained from various intersections. Based on a concept that the driving risk increases when a driving situation is out of the range of the normal driving, an on-board driving assistance system has been developed that gives a caution information to the driver when the driver behaves differently from the normal driving.