# 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 Urban Road Accidents  
Heavy truck accidents on urban roads are significantly correlated with four variables: lighting conditions, road safety attributes, driver age, and vehicle driving status. And driving experience, inter-vehicle accident types, accident forms, road surface conditions, intersection section types, physical isolation conditions, roadside protection measures, alignment, weather, visibility, and violations are not significant factors. The results are shown in Table 6.  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Influencing Factors** & \(\beta\) & **Standard Error** & **Wald** & **df** & **Significance** & **Exp (\(\beta\))** \\ \hline
**Lighting Conditions** & & & 15.603 & 2 & 0.000 & \\
1 = Daytime & \(-0.160\) & 0.423 & 0.143 & 1 & 0.705 & 0.852 \\
2 = Night with Streetlights & 0.608 & 0.427 & 2.026 & 1 & 0.155 & 1.837 \\
**Road Safety Attributes** (1 = Hazard) & 0.687 & 0.229 & 9.027 & 1 & 0.003 & 1.987 \\
**Age** & & & 11.654 & 3 & 0.009 & \\
1 = 30–40 & 0.623 & 0.342 & 3.317 & 1 & 0.069 & 1.864 \\
2 = 40–50 & 0.762 & 0.347 & 4.827 & 1 & 0.028 & 2.142 \\
3 = 50+ & 1.343 & 0.404 & 11.066 & 1 & 0.001 & 3.832 \\
**Driving Status** (1 = Straight) & 0.421 & 0.190 & 4.882 & 1 & 0.027 & 1.523 \\
**Constant** & \(-1.645\) & 0.532 & 9.580 & 1 & 0.002 & 0.193 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Regression Analysis Results of Heavy Truck Accidents on Urban Roads.  
1. Driver aspects: Age is a significant factor affecting urban heavy truck traffic accident severity, with a significance of 0.009 < 0.05. The probability of fatal accidents occurring among drivers of different age groups indicates that as age increases, the probability of fatal accidents increases, with drivers aged over 50 having the highest probability, 3.832 times that of drivers under 30. This could be due to the decline in physical function and extended reaction time with age, making it difficult for older drivers to respond quickly in emergencies.
2. Vehicle aspects: The driving status of the vehicle is a significant factor affecting urban heavy truck traffic accident severity. When the vehicle is driving straight, the probability of fatal accidents is 1.523 times that of non-straight driving. Compared to non-straight driving status, heavy trucks tend to drive at relatively higher speeds when going straight. Additionally, heavy trucks have the prominent characteristic of carrying large loads. The combination of these features makes it difficult for straight-moving heavy trucks to brake and stop promptly in the event of sudden incidents, often leading to severe traffic accidents.
3. Road conditions: Road safety attributes are significant factors affecting urban heavy truck traffic accident severity. When there are hazards on the road, the probability of fatal accidents is 1.987 times that of roads without hazards. Road hazards, including poor visibility, unclear traffic markings, improper placement of traffic signs, and pavement damage, can negatively impact drivers' perception, decision-making, and control, leading to serious accidents.
4. Environmental aspects: Lighting conditions are significant factors affecting urban heavy truck traffic accident severity. The probability of fatal accidents under street lighting at night is 1.837 times that of no street lighting. The cause of this phenomenon may be that better nighttime lighting conditions lead to decreased vigilance among heavy truck drivers, resulting in higher speeds and, consequently, increasing the severity of traffic accidents. The probability of fatal accidents with no street lighting at night is 1.174 times that of daytime. This indicates that fatal accidents are more likely to occur at night compared to daytime on urban roads.  
The analysis of the mechanism of urban heavy truck traffic accident severity reveals that older driver age, straight driving status, hazardous road sections, and night street lighting are risk factors leading to fatal accidents on urban roads.