The safety risks of roadside trees: An analysis of injury outcomes in vehicle-tree collisions.

Roadside trees represent the most frequently struck fixed object in fatal crashes in the United States and constitute a substantial safety concern, particularly on high-speed rural roadways. Although trees are often retained or planted along roadways for aesthetic and environmental benefits, their presence within the roadside environment can significantly increase the risk of severe injury outcomes. This study examines the factors influencing driver injury severity in vehicle-tree collisions using a five-year dataset (2020-2024) from the state of Alabama. Following data cleaning and validation, 17,555 crash records were analyzed. Descriptive analysis indicated that fatal and serious injury crashes accounted for 15.20% of cases, with 73.14% occurring in rural areas, and 10.50% involving driving under the influence. To better understand the determinants of injury severity, both traditional regression models and advanced machine learning techniques were employed. The results consistently identified seat belt use as the most influential factor, followed by driver condition (impaired versus non-impaired) and driver gender. Additional significant predictors included crash location, weather conditions, and vehicle type. While these factors have been associated with injury severity in broader crash contexts, their prominence in vehicle-tree collisions reinforces the importance of established safety interventions. From a policy perspective, the findings point to restraint use, impaired driving, and the rural high-speed context as the associations most consistently identified, and are discussed alongside existing roadside design guidance on clear-zone treatment and barrier protection, to mitigate the severity of these high-risk crash events.