Cooperative Adaptive Cruise Control (CACC) is an advanced technique for organizing and managing a vehicle platoon, which employs the Vehicle-to-Vehicle/Vehicle-to-Infrastructure (V2V/V2I, or V2X) wireless communication to minimize the inter-vehicle distance while guaranteeing string-stability. Consequently, the conventional CACC system relies heavily on the quality of communications, which means that the regular CACC platoon is sensitive to the communication failure. Therefore, in this paper, a Safety Reinforced Cooperative Adaptive Cruise Control (SR-CACC) strategy is proposed to resist unexpected communication failure. Different from the regular CACC system, the safety enhanced platoon control system is embedded with a dual-branch control strategy. When a fatal wireless communication failure is detected and confirmed, the SR-CACC system will automatically activate the alternative sensor-based adaptive cruise control strategy. Moreover, to make the transforming process smooth, a linear smooth transition algorithm is added to the SR-CACC system. Then, to verify the performance of the proposed SR-CACC system, we conducted a simulation experiment with a heterogonous platoon constructed with eight vehicles. The experiments results reveal that, under the extremely poor communication environment, the proposed SR-CACC strategy can significantly improve the safety performance of the organized vehicle platoon.

Cooperative adaptive cruise control (CACC) is a promising technology to improve traffic efficiency and enhance road safety. In this paper, a modified CACC control model considering the communication time delay is proposed, which is used to investigate the longitudinal safety impacts of the communication time delay to the CACC platoon. Then, the communication time delay model is integrated into the CACC model to simulate the realistic information transfer process in the CACC platoon. Then a microscopic CACC platoon simulation is designed and conducted to verify the feasibility and reliability of the modified CACC control algorithm. The obtained results reveal that the modified CACC control algorithm can not only reduce about 96.6% of inter-vehicle spacing error, but also enhance the vehicles’ ability to sense the upstream traffic changes. Furthermore, to quantitatively analyze the longitudinal safety influence of the time delay caused by representative communication systems, sensitivity analysis experiments of headway time were designed and conducted. In the sensitivity analysis, the time exposed time-to-collision (TET) and the time-integrated time-to-collision (TIT) were introduced as the key performance indicators (KPIs) to quantify the rear-end collision risks. Sensitivity analysis results demonstrate that the performance of the CACC platoon is strictly related to the applied wireless communication style. Furthermore, the CACC system supported by the 5th generation (5G) communication system shows great advantages in narrowing the minimal headway time gap and reducing the rear-end collision risks.

This paper comprehensively investigates the feasibility of a modified cooperative adaptive cruise control (CACC) strategy to support car platooning in freeway weaving segments. Firstly, to improve the system response to cut-out and cut-in disturbance, the control structure of the typical original CACC system was modified and a synthesis control structure was designed that integrates the feedforward control module to the conventional feedback CACC system. Based on the modified control structure, a variable acceleration limited (VAL) control algorithm is proposed, which is specifically applied in the feedforward control model to suppress the propagation of the cut-in and cut-out disturbances in the CACC platoon. To investigate the performance of the VAL-CACC strategy, a series of comparative simulation experiments were carried out under simulated freeway weaving areas. In these tested scenarios, the occurance of frequent lane changing is considered, and the cut-out and cut-in disturbance of the CACC platoon are investigated, respectively. The obtained experimental results revealed that, compared with the original CACC system, the proposed VAL-CACC strategy can ameliorate the acceleration fluctuation amplitude, reducing it by 12.5% in the tested cut-out scenario. On the other hand, in the cut-in comparative experiments, it is found out that the VAL-CACC strategy can more significantly reduce by about 48.33% the jitter amplitude caused by the merging-in behavior of the non-platooned vehicle. These results demonstrate that the proposed synthesis VAL-CACC strategy can dramatically improve the CACC platoon’s ability to resist cut-in and cut-out disturbances.