# Lateral Oscillation Characteristics of Vehicle Trajectories on the Straight Sections of Freeways
## 2 Literature Review
### Vehicle Trajectory Oscillation and Lane Keeping  
Lane keeping is the tendency of the driver to drive steadily in a lane by remaining in the center as closely as possible. Another way to put it is the lateral placement of vehicles across lanes on roads [21]. Nevertheless, the lateral oscillation of vehicles during driving is a fundamental cause of many traffic accidents, such as lateral collisions and vehicle rollover. Road alignment affects trajectory oscillation, and the consistency of vehicle trajectory and road alignment forms the cornerstone of road geometry design. The existing lane was created with the presumption that the vehicle's centerline and the lane's centerline coincide, and that the space between the two represents the vehicle's lateral offset [22]. Individual differences, like driving habits and experience, prevent human-driven vehicles from consistently keeping in the center of the lane, which causes the vehicles to drift toward the edge of the road. The drivers will adjust the vehicles back to the centerline if the lateral amplitude exceeds a particular threshold they perceive. It will also lead to safety issues because the cars would continuously oscillate and swing inside the lane. This is in contrast to connected autonomous vehicles. Some researchers try to investigate the properties of vehicle trajectory oscillation to help comprehend lane departure. [PERSON] et al. [23] demonstrated the consistency between vehicle trajectory and speed. They found a positive correlation between trajectory offset and traveling speed in curved sections. From this, it can be inferred that the speed shift results in a vehicle trajectory offset. [PERSON] et al. [24] analyzed the effect of combined alignment on lane deviation and concluded that horizontal curvature and slope are the primary determining factors. [PERSON] et al. [25; 26] looked into how the weather affected lane-keeping ability and driving behavior. They discovered that inclement weather increased both the frequency and severity of lane departures. [PERSON] et al. [27] attributed the lateral offset of trajectory during a non-active lane change to two main reasons: driving inattention and distraction. In order to examine the lateral location of trajectories, another way relies on video processing and vehicle-detecting technologies. [PERSON] et al. [28] found that vehicles tend to deviate toward the centerline during low traffic volumes and toward the roadside during high traffic volumes by analyzing video data from a multi-lane highway. [PERSON] et al. [29] used specialized software to extract vehicle trajectory data from video sequences and found discrepancies in the lateral offsets of different vehicle types within the road cross-section. Table 1 shows the lane-width specifications for freeways in different countries and a comparison of the present studies. In summary, many achievements have been made in studying the driving trajectory. The scenarios for these studies are usually tough roads, such as mountain roads, curved sections, and intersections. Vehicle trajectory is not only affected by the external environment (e.g., road alignment, weather conditions, and traffic flow), but also by the driver's personal attributes (e.g., speed control, lane choice, and other driving habits). It is common knowledge that the mainline of the freeway is dominated by straight sections where about 70% of traffic accidents occur. The safety level of the freeway will be directly impacted by how well the automobiles operate on straight sections. Unfortunately, a few studies have been conducted to explore the characteristics of trajectories on straight sections of freeways, and the lateral oscillations of different vehicles have not been entirely carried out. Moreover, the lane width depends heavily on the lateral oscillation of the vehicle, but the relationship between them is still unidentified.