# Analysis of the Severity of Heavy Truck Traffic Accidents Under Different Road Conditions
## 8 Conclusions  
This study, based on five years of heavy truck traffic accident data from a region in China, uses a binary logistic regression model to analyze the factors and mechanisms affecting the severity of heavy truck traffic accidents. Considering that different road types have distinct design standards, control measures, and conflict types, we established separate models for analyzing the severity of heavy truck traffic accidents under urban roads, highways, and expressways. The results indicate significant differences in the causes of severe heavy truck accidents across different road types. Under urban road conditions, key factors that exacerbate the severity of heavy truck accidents include drivers over 50 years old, vehicles driving straight, road hazards, and nighttime lighting with street lamps. Specifically, the probability of a fatal accident for drivers over 50 years old is 3.832 times higher than for drivers under 30. When the vehicle is driving straight, the probability of a fatal accident is 1.523 times higher than for non-straight driving. When there are hazards on the road, the probability of a fatal accident is 1.987 times higher than on roads without hazards. The probability of a fatal accident at night with street lighting is 1.837 times higher than at night without street lighting. Under highway conditions, the main factors contributing to increased severity are vehicles driving straight, side collisions between vehicles, lack of roadside protection, road hazards, and visibility below 50 m. Specifically, the probability of a fatal accident when driving straight is 1.57 times higher than when driving non-straight. Side collisions have the highest probability of causing fatal accidents, with a likelihood 1.294 times higher than non-vehicle-related accidents. The probability of a fatal accident occurring in areas without roadside protection is 1.792 times higher than in areas with protection. The probability of a fatal accident on a road section is 1.506 times higher than at intersections. Roads with hazards are 1.57 times more likely to cause fatal accidents than hazard-free roads. As visibility decreases, the probability of fatal accidents increases. The likelihood of a fatal accident at visibility levels below 50 m is 2.732, 3.534, and 5.181 times higher than at visibility levels of 50-100 m, 100-200 m, and over 200 m, respectively. Under expressway conditions, key factors include speeding, traffic signal violations, non-compliance with vehicle technical standards, vehicles driving on curved or sloped roads, collisions with pedestrians, and visibility between 100 and 200 m. Specifically, the top three violations leading to fatal accidents are speeding, violating traffic signals, and non-compliance with vehicle technical standards, with probabilities 2.582, 2.116, and 2.032 times higher than other factors, respectively. The probability of a fatal accident in non-vehicle-related accidents is the highest, being 4.587, 1.575, and 4 times higher than in side collisions, rear-end collisions, and other angle collisions, respectively. The probability of a fatal accident on curved or sloped road sections is 5.228 times higher than on straight sections. As visibility increases, the probability of fatal accidents first increases and then decreases. When visibility is below 50 m, the likelihood of a fatal accident is lowest, while at 100-200 m, the likelihood is highest--3.292 times that of visibility below 50 m.  
Conceptualization, F.C. and S.M. ; Investigation, Z.T. and M.G. ; Methodology, Z.T. and F.C. ; Formal analysis, F.C. ; Visualization, Z.T. ; Validation, Z.T. and F.C. ; Writing--original draft, Z.T. and F.C. ; Writing--review and editing, M.G., F.C. and S.M. ; Resources, F.C. ; Data curation, F.C. ; Supervision, F.C. ; Project administration, S.M. ; Funding acquisition, F.C. and M.G. All authors have read and agreed to the published version of the manuscript.