Abstract: A quantitative analysis is conducted on the chaos phenomenon in the car-following fleet based on the headway kept by the two consecutive vehicles and the follow-up vehicle's speed. By studying the microscopic characteristics of the vehicles fleet in the process of stimuli and reaction, it is proved that there exists a chaos occurrence in the car-following fleet. In order to reasonably model the expected headway in traffic stream, four expected desired headway models are proposed. Then, the Rossler chaos attractors are introduced in those four models to choose the models that can describe the actual traffic characteristics. The calibration and validation procedures are conducted using high accurate GPS equipped vehicles to collect data from expressways. Based on the results it can be seen that the modified headway models can best reflect the car-following characteristics of the real traffic flow.