AbstractThis work investigated the cooperative control of a highway on-ramp under a connected and automated vehicles (CAVs) environment based on improved variable time headway (IVTH). A mainline section with a connected on-ramp and off-ramp of an intelligent highway were used as research objects. An IVTH model was developed and its stability was proved. The traffic flow model of the section was established and then verified in experiments. A cooperative control strategy of highway on-off-ramps is proposed. The cooperative merging control model (CMCM) based on IVTH (CMCM-IVTH) was constructed in which the influence of off-ramp separation is considered. The model predictive control method based on particle swarm optimization is used to obtain the acceleration and deceleration of platoon leaders with CMCM-IVTH and the time headway of the following vehicles with the traffic flow model based on IVTH. The control effects were determined via simulation experiments. The results indicate that the acceleration and deceleration times of vehicles, fuel consumption, and collision possibility decreased significantly using the proposed method. Under a 20% diverging rate, the maximum number of slow-moving vehicles was reduced by as much as 75.0% and 33.3%, total delay time was reduced by as much as 72.9% and 18.9%, the average traveling velocity was increased by as much as 21.9% and 2.1%, compared with the no-optimization-control method and a method with only cooperative merging control, respectively. The operating efficiency and safety level can be enhanced.