# Analysis of the Severity of Heavy Truck Traffic Accidents Under Different Road Conditions
## 5 Mechanism Analysis of Heavy Truck Traffic Accident Severity
### Mechanism Analysis of Expressway Accidents  
Heavy truck accidents on expressways are significantly correlated with four variables: inter-vehicle accident types, driver violations, visibility, and road alignment. And age, driving experience, vehicle driving status, accident forms, road surface conditions, intersection section types, physical isolation conditions, road safety attributes, roadside protection measures, lighting conditions, and weather are not significant factors. The results are shown in Table 8.  
1. Driver aspects: Driver violations are significant factors affecting heavy truck traffic accident severity on expressways. The significance of violations is 0.039 < 0.05, indicating that violations are related to heavy truck traffic accident severity on expressways. Using other reasons (natural disasters, etc.) as a reference, the top three violations with the highest probability of causing fatal accidents are speeding, violating traffic signals (traffic signs, traffic markings), and vehicles not meeting technical standards, with probabilities 2.582, 2.116, and 2.032 times that of other reasons, respectively. Speeding increases the braking distance and the impact force during collisions. Violations of \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Influencing Factors** & \(\beta\) & **Standard Error** & **Wald** & **df** & **Significance** & **Exp (\(\beta\))** \\ \hline
**Accident Types** & & & 14.59 & 3 & 0.002 & \\
1 = Side Collision & 0.258 & 0.23 & 1.258 & 1 & 0.262 & 1.294 \\
2 = Rear-end Collision & \(-\)0.216 & 0.288 & 0.561 & 1 & 0.454 & 0.806 \\
3 = Other Collision & \(-\)0.943 & 0.323 & 8.541 & 1 & 0.003 & 0.389 \\
**Visibility** & & & 32.838 & 3 & 0 & \\
1 = 50–100 m & \(-\)1.005 & 0.302 & 11.109 & 1 & 0.001 & 0.366 \\
2 = 100–200 m & \(-\)1.263 & 0.321 & 15.509 & 1 & 0 & 0.283 \\
3 = 200+ meters & \(-\)1.646 & 0.292 & 31.875 & 1 & 0 & 0.193 \\
**Intersection Section Type** (1 = Intersection) & \(-\)0.44 & 0.204 & 4.668 & 1 & 0.031 & 0.644 \\
**Roadside Protection Measures** (1 = Protection) & \(-\)0.583 & 0.22 & 7.015 & 1 & 0.008 & 0.558 \\
**Road Safety Attributes** (1 = Hazard) & 0.547 & 0.195 & 7.863 & 1 & 0.005 & 1.727 \\
**Driving Status** (1 = Straight) & 0.451 & 0.215 & 4.392 & 1 & 0.036 & 1.57 \\
**Constant** & 0.728 & 0.33 & 4.862 & 1 & 0.027 & 2.071 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Regression Analysis Results of Heavy Truck Accidents on Highways. traffic signals by heavy trucks primarily include crossing solid lines while changing lanes and disregarding lane separation signs for passengers and cargo. Such violations can lead to side collisions or rear-end accidents involving passenger cars, which increases the risk of fatalities among passengers and drivers in these cars. Failure to meet technical standards includes the absence of side and rear under-run protection devices or reflective markings on the body, making heavy trucks difficult to detect and unable to use crash barriers to absorb energy during collisions, increasing the probability of fatal accidents. 2. Vehicle aspects: Inter-vehicle accident types are significant factors affecting heavy truck traffic accident severity on expressways. Regarding accident types, when the accident type is a non-vehicle accident, i.e., a vehicle-pedestrian accident, the probability of fatal accidents is the highest, being 4.587, 1.575, and 4 times that of side collisions, rear-end collisions, and other angle collisions, respectively. Under expressway conditions, heavy truck collisions with pedestrians who are illegally on the expressway or with occupants of disabled vehicles who have not evacuated in time are the primary types of vehicle-to-person accidents. Additionally, heavy trucks operate at high speeds on expressways, have a heavy load, and require a long braking distance. Consequently, if a collision occurs, the probability of fatalities among those struck is extremely high. 3. Road conditions: Road alignment is a significant factor affecting heavy truck traffic accident severity on expressways.