Lateral collision is one of the top two accidents in the world and often occurs in the lane change. Trajectory optimisation is an effective method to solve traffic conflicts in the lane-changing process. However, current trajectory optimisation methods are not friendly to human-computer-based driving assistance. This study proposes a timedependent lanechange trajectory optimisation considering comfort and efficiency. First, spacing constraints between the lane-changing vehicle and surrounding vehicles are determined and quantified. Second, lane-changing trajectory data are obtained by driving simulation experiments and extracted by data features. Third, a quintic multinomial model of lane-changing trajectory is proposed. The results reveal that the predicted trajectory is close to the observed value. Then, the obtained trajectory is optimised by the objective function considering lane-changing efficiency and comfort. Finally, a case study is used to demonstrate the application of the model. When a lane-changing vehicle changes a lane at an initial speed of 90 km/h to the faster lane at the terminal speed of 110 km/h, the optimal lane-changing time is 3.4 s, with the lateral acceleration 1.79 m/s 2 and the maximum yaw angle 0.081 rad. 1 INTRODUCTION Lateral and rear-end collisions are the two most collision manoeuvres in the world. According to the national highway traffic safety administration (NHTSA) traffic accident data from 2014 to 2018, rear-end collisions accounted for the highest proportion, reaching 40%. The second was angle collision, accounting for 24%, of which the proportion of lateral collisions was 13% [1]. In China, lateral collisions have a higher percentage. The 2018 traffic accident data revealed that sideswipe accounted for the highest proportion, reaching 42.7%, followed by rearend collision, accounting for 7.95%. Car following is a process of following but not exceeding obstacles, during which there is only one potential traffic conflict, while lane-changing is a process of surpassing obstacles to reach the ideal position, and there are multiple potential traffic conflicts. This is also the reason why side-impact accidents occur frequently in China. The surrounding traffic environment influences the lanechanging process of the lane-changing vehicle. In the lanechanging process, drivers need to analyse and make a This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.