Exploring Driver Trajectory Preferences for Unprotected Left Turns and the Impact on Traffic Safety

The behaviour of drivers making left turns is complex, significantly affecting the safety of intersection operations. Some drivers disregard the right-of-way rules when making left turns, leading to contention with vehicles going straight, causing chaotic trajectories and widening the potential conflict area with straight-moving vehicles. This study analyses the left turn trajectory preference of drivers under different intersection conditions and compares the effects of various intervention measures in enhancing intersection safety. Twenty-seven scenarios were created with different sign and marking designs and traffic conditions using a driving simulator. Forty-four participants were recruited to gather driving data, such as speed and position, to extract key evaluation indicators representing drivers’ left turn behaviour. In addition, a one-way analysis of variance is conducted to explore the trajectory perspective on horizontal curves, driver gap acceptance time and post-encroachment time during left turn. The results revealed that drivers’ trajectories leaned more towards the left side when making left turns under crossing decisions. Whereas under yielding decisions, drivers’ trajectories stayed closer to the right side. Additionally, the absolute deviation of trajectories under yielding decisions was greater than those under crossing decisions. The findings confirm that the left-turn guidelines can influence left-turn driving behaviour to enhance safety.