Leveraging probe data to assess left-turn driver behaviour under varying permissive signals

Flashing yellow arrows (FYAs) and circular green signals (CGs) are prevalent permissive left-turn indications at intersections. These signals can significantly influence drivers’ left-turn behaviour and, in turn, affect intersection safety. Despite this, few studies have investigated differences in left-turn behaviour under these indications. This study leverages probe data to assess speeds, accelerations, and decelerations at 106 FYA and 116 CG intersection approaches in Tucson, Arizona, while controlling for geometric and temporal factors. Results showed that FYA approaches generally exhibited lower speeds and higher decelerations than CGs. Vehicles in the outer lanes of dual left-turn approaches with FYAs showed greater acceleration fluctuations. Additionally, vehicles on dual left-turn lanes, particularly with FYAs, exhibited lower average speeds than those on single left-turn approaches. These findings enhance the understanding of how FYAs and CGs affect driver behaviour at approaches with varying geometric configurations, aiding transportation agencies in making informed decisions to improve intersection safety.