Under the context of smart capacity expansion, dynamically opening the emergency lane has been gradually adopted to alleviate heavy traffic pressure on expressways, showing relatively stable performance under normal conditions. However, once a traffic accident occurs, the emergency lane no longer serves solely as a traffic space but must also accommodate emergency response vehicles, and its control strategy directly affects traffic safety and the subsequent recovery process.In existing practices, the lack of differentiated responses to various accident scenarios often makes it difficult to balance traffic operations and emergency access. To address this issue, this study starts from the impact of accidents and quantifies accident severity by introducing an accident severity index. A fuzzy clustering method is then applied to classify accident levels. Based on the classification results and the location of the accident, corresponding emergency lane control strategies are developed. For high-risk segments such as bridges, stricter control measures are adopted to ensure operational safety.For validation, multiple accident scenarios are constructed on the SUMO platform, and three strategies—lane closure, permanent opening, and graded dynamic control—are compared. The results indicate that, while ensuring the passage of emergency vehicles, the graded dynamic control strategy can improve traffic operations under incident conditions, with more stable performance observed in high-risk scenarios. These findings provide a reference for the practical management of emergency lanes under smart capacity expansion conditions.