# Determining Factors Influencing Operating Speeds on Road Tangents
## 3 Results
### Dual-Carriageway Road Tangents
#### 3.2.1 Left (Overtaking) Lane  
In order to explore the relationships between the operating vehicle speed and the continuous factors in the left (overtaking) lane of dual-carriageway road tangents, a similar approach to that used for single-carriageway roads was employed. Following the Shapiro-Wilk test, the Pearson correlation coefficient was applied for those variables that were found to be normally distributed, while Spearman's rank correlation was utilized for the remaining variables that did not meet the assumption of normality. The results of both the Pearson and Spearman's correlations are summarized in Table 5, which highlights the strength and direction of the relationships between the operating vehicle speed and each of the continuous factors.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Factors—Dual-Carriageway Roads** & **Type** & **Normal Distribution** & **Test Used** \\ \hline Total tunnel length in last 20 km & Continuous & NO & Spearman \\ Speed limit & Categorical—Multi-level & — & ANOVA \\ Lane width & Categorical—Multi-level & — & ANOVA \\ Design speed & Categorical—Multi-level & — & ANOVA \\ Emergency lane presence & Binary & — & \(t\)-test \\ Previous object distance & Continuous & YES & Pearson \\ Following object distance & Continuous & YES & Pearson \\ Longitudinal slope & Continuous & YES & Pearson \\ Terrain type & Categorical—Multi-level & — & ANOVA \\ Heavy goods vehicles share (left lane) & Continuous & NO & Spearman \\ Heavy goods vehicles share (right lane) & Continuous & YES & Pearson \\ Heavy goods vehicles share (both lanes) & Continuous & YES & Pearson \\ AADT & Continuous & NO & Spearman \\ ASDT & Continuous & NO & Spearman \\ Traffic flow density (left lane) & Continuous & NO & Spearman \\ Traffic flow density (right lane) & Continuous & YES & Pearson \\ \hline \hline \end{tabular}
\end{table}
Table 4: Statistical approach for factors on dual-carriageway road tangents.  
Figure 14: Shapiro–Wilk test for continuous factors—dual-carriageway road tangents (Values marked with * indicate statistically significant results at the 0.05 level).  
Figure 15: Determination of statistically significant difference between measured speeds in the left and right lane on motorways (Values marked with * indicate statistically significant results at the 0.05 level).  
For multi-level categorical variables, the relationship between the operating speeds and the different levels within each variable was analyzed using an analysis of variance (ANOVA). This approach allowed for the assessment of significant differences in the operating speeds across multiple categories. The ANOVA results are shown in Figure 17.  
An analysis of variance (ANOVA) was conducted to examine the influence of several categorical factors on the operating vehicle speed (V85) in the left (overtaking) lane of dual-carriageway road tangents. The results revealed that most factors did not exhibit statistically significant differences in the operating speed. Specifically, the factors speed limit (\(p\) = 0.3981), lane width (\(p\) = 0.2427), and design speed (Vp) (\(p\) = 0.2427) all produced \(p\)-values greater than the 0.05 threshold, suggesting no significant effect on V85 in the left lane. However, terrain type (\(p\) = 0.0970) showed a borderline significant effect on the operating speed, with an F-ratio of 2.6842, indicating potential differences in speed across terrain types, but failing to reach the conventional significance level of 0.05. Given that the \(p\)-value for terrain type was close to 0.05, it was decided to perform a post hoc  
Figure 17: ANOVA results for multi-level categorical factors—left (overtaking) lane of dual-carriageway road tangents.  
Tukey-Kramer test to further investigate the pairwise operating speed differences between the terrain categories. The Tukey-Kramer test results are shown in Figure 18.