# Determining Factors Influencing Operating Speeds on Road Tangents
## 4 Discussion and Conclusions
The ANOVA results showed that only terrain type had a statistically significant effect on the operating speed (F = 10.99, \(p=0.0005\)), with post hoc comparisons revealing that vehicles drove significantly faster on hilly and flat terrain than in mountainous areas. This finding aligns with the existing literature [51], which consistently links reduced speeds to increased perceived and actual driving difficulty in mountainous regions. Additionally, lane width, design speed (Vp), and edge line quality exhibited marginal \(p\)-values (all around 0.05), suggesting potential effects that warrant further investigation. Consequently, a Tukey-Kramer post hoc analysis was conducted for these variables. For lane width, the comparison between 3.00 m and 3.25 m widths reached statistical significance (\(p=0.0435\)), with wider lanes supporting higher operating speeds, which is consistent with findings from the road safety literature. Edge line quality, while not yielding statistically significant differences, showed a tendency toward higher speeds on road sections with higher edge line quality ratings, though these differences did not achieve significance in pairwise comparisons. Importantly, these results underscore the need for nuanced interpretation when analyzing categorical variables. Unlike continuous predictors, which are often evaluated through correlation, categorical variables require group-wise comparison methods, such as ANOVA and post hoc testing, to uncover meaningful patterns. In summary, while the majority of the investigated factors did not show statistically significant associations with the operating speed, the influence of terrain type was clearly evident. Additionally, lane width demonstrated borderline significance and could contribute to speed behavior under certain conditions. These findings reinforce the complexity of speed choice on single-carriageway road tangents, and highlight the importance of con sidering both environmental context and roadway design features in road safety analyses. Future studies should expand the dataset to enhance the statistical power, to incorporate objective measures for road quality assessments, and to explore the interactive effects among multiple road attributes. The analysis of dual-carriageway road tangents included a separate examination of the left (overtaking) and right (driving) lanes, recognizing their distinct traffic functions. Various factors were tested for their statistical association with operating speed, using correlation analysis for continuous variables (Pearson or Spearman's depending on the data distribution), \(t\)-tests for the binary variables, and ANOVA with post hoc Tukey-Kramer testing for categorical variables with more than two levels. Among the continuous variables, the most consistent and statistically significant associations were observed for traffic flow-related parameters, especially in the left (overtaking) lane. A strong negative correlation was found between traffic flow density and operating speed in both lanes, particularly in the left lane (\(p=-0.7434\), \(p=0.0002\)) and the right lane (\(p=-0.7901\), \(p<0.0001\)). Similarly, the average summer daily traffic (ASDT) was significantly negatively correlated with the operating speed in both lanes, more prominently in the right lane (\(p=0.0115\)). These results confirm the intuitive expectation that increased traffic volumes and densities reduce the potential for maintaining higher operating speeds. A statistically significant positive correlation was also identified between the share of heavy goods vehicles in the left lane and the operating speed in that same lane (\(p=0.6152\), \(p=0.0039\)). This may indicate driver tendency to accelerate in overtaking lanes when passing slower heavy goods vehicles, thereby increasing the average speeds. However, other continuous factors, such as longitudinal slope, object distances (previous and following), and total tunnel length in the preceding 20 km, did not show statistically significant associations with the operating speed in either lane.