Abstract:

Establishing an accurate and reasonable evaluation model of driving safety status is one of the key technologies of the forward collision warning system. As the most classical evaluation model of driving safety status, safe distance has the advantages of universality and robustness. However, traditional safety distance models often assume the initial state of the rear car receiving the warning signal as uniform motion and rely solely on the analysis of vehicle kinematics to determine the safety distance. Due to the complex force situation and multiple influencing factors during vehicle braking, analyzing braking distance only from a kinematic perspective may reduce the accuracy of the model and thus affect the reliability of the warning system.

To address these issues, this paper considers three different motion states of the rear car, including initial uniform motion, acceleration, and deceleration. Combining kinematics and dynamics methods, the force situation of a vehicle during each stage of the braking process is comprehensively analyzed for different initial states of the rear car. Longitudinal dynamic modeling is then conducted to establish safety distance models based on the front car’s stationary state, uniform or accelerated motion state, and emergency braking state. Simulation experiments are carried out to obtain the differences and variation patterns of the warning safety distance under different initial states of the rear car.

The simulation results show that there are differences in the warning safety distance for the following vehicle’s initial acceleration/deceleration state and initial uniform motion state, and the difference size is related to the initial acceleration/deceleration value and driving speed of the following vehicle. The difference in the warning safety distance generated by different initial states of the following vehicle increases with an increase in the initial acceleration/deceleration value, with a distance difference of the front vehicle’s braking condition being the most significant of up to 18.69 m.When the following vehicle initially decelerates, the reduction rate of the warning safety distance can reach a maximum of 49.53% compared with the initial uniform motion state. Regardless of the initial state, when the following vehicle’s driving speed increases, the warning safety distance also increases. The difference in the warning safety distance still increases with an increase in the driving speed, but the relative increase/decrease rate of the warning safety distance in the initial acceleration/deceleration state decreases compared with the initial uniform motion state. When the following vehicle reaches a relatively high driving speed, the impact of different initial states on the warning safety distance becomes less significant.

In summary, the following vehicle’s initial state is an important factor affecting the safety distance. By analyzing the different initial states of the following vehicle and combining kinematic and dynamic methods to model the safety distance with multiple factors, it is possible to more accurately determine the driving safety status, reduce the false alarm rate of the warning system, and improve the accuracy and coordination adaptability of the forward collision warning system.