# Determining Factors Influencing Operating Speeds on Road Tangents
## 4 Discussion and Conclusions  
Road traffic safety is a critical global issue, with approximately 1.19 million fatalities occurring annually due to road traffic accidents, as reported by the World Health Organization. The socioeconomic burden of these accidents is substantial, with costs estimated at 3% of GDP in the European Union alone. Among the key contributors to road traffic accidents is excessive or inappropriate speed, which is linked to higher crash rates and severity levels. Studies have indicated that a 1% increase in average speed results in a 4% increase in fatal crash risk. Indeed, road tangents, characterized by their straight alignment and lack of geometric constraints, are particularly associated with higher operating speeds, making them crucial areas for traffic safety research. Despite their role in enhancing traffic flow efficiency, tangents pose significant safety risks due to the potential for excessive speeds and increased crash severity. Previous research has highlighted various factors influencing operating speeds, such as road geometry, traffic conditions, and human behavior, but a comprehensive understanding of these influences remains incomplete. This study aimed to address this gap by analyzing the operating speeds (V85) on road tangents of both single-carriageway and dual-carriageway roads, investigating their correlation with geometric, traffic-related, and environmental factors. To achieve this, a combination of field data  
Figure 21: Tukey–Kramer test results—terrain type—right (driving) lane of dual-carriageway road tangents. collection and statistical analysis was performed, including the Pearson correlation test and the Tukey-Kramer test for categorical variables. The research was conducted on carefully selected road segments in Croatia, covering various speed limits and road environments to ensure a diverse and representative dataset. By identifying key relationships between the operating speed and influential factors, this study contributes to a more detailed understanding of speed behavior on road tangents and its implications for road safety and infrastructure planning. The analysis of single-carriageway road tangents revealed limited statistically significant relationships between the investigated factors and the operating speed (V85). The initial assumption that road geometry, traffic flow characteristics, and roadside features substantially influence speed behavior was only partially supported by the data. Among the continuous variables, correlation analyses using the [PERSON] and [PERSON]'s tests indicated that none of the examined factors were significantly correlated with operating speed on single-carriageway road tangents at the 5% significance level. Although the average annual daily traffic (AADT) and the crash ratio demonstrated moderate negative correlations with V85 (\(p=-0.3970\), \(p=0.0547\) and \(p=0.3628\), \(p=0.0815\), respectively), the associations did not reach statistical significance. Similarly, tangent lengths, longitudinal slope, and heavy goods vehicles share exhibited weak or negligible correlations with the operating speed, suggesting that these variables alone are insufficient predictors of speed behavior on single-carriageway road tangents. For the binary variables, independent sample \(t\)-tests did not identify any statistically significant differences in the operating speed across categories such as guardrail presence, shoulder lane presence, overtaking allowance, road category, or the disruptive presence factor. These results imply that such binary features may not play a dominant role in speed selection on tangent segments or that their effects are moderated by other, unmeasured factors, such as driver behavior or the contextual environment. More insight was gained from the multi-level categorical variables assessed through one-way ANOVA and post hoc Tukey-Kramer testing.