Highlights • The study proposes a novel lane change risk assessment index. • Trajectory data from a weaving section in China were used for a case study. • The suggested index incorporates both exposure time and conflict severity. • The indexes indicate the middle section is the most dangerous. • The last 100 m section before the exit is the safest.

Abstract Vehicles frequently change lanes at weaving segments, and there is a high probability of collision. To assess the risk of lane change, this study proposes a novel lane change risk assessment index (LCRAI), which takes both exposure time and conflict severity into consideration. First, the generalized time-to-collision (GTTC) and exposure-to-risk index (ERI) are proposed to evaluate conflicts during lane change, and then a spatiotemporal overlap analysis is applied to exclude the cases when two vehicles arrive at the conflict area at different times. Second, the change of velocity after a crash occurrence is calculated and used to evaluate the severity risk (SRI). Finally, ERI and SRI are combined to compute the LCRAI. A case study of a weaving segment is conducted, and the weaving segment is divided into four sections to compare their risks. Conflict frequency on the section close to the exit is the largest and it is smallest after passing the exit, while conflict severity is most serious just after entering the main line on the middle lane. As for both conflict frequency and severity, LCRAI shows that the middle section is the most dangerous while the last 100 m section is the safest in the weaving segment. The index proposed will contribute to the risk assessment of lane change in connected environments and improve safety in weaving segments of expressway combined with real-time safety countermeasures.