# Determining Factors Influencing Operating Speeds on Road Tangents
## 4 Discussion and Conclusions
Regarding the binary variable of emergency lane presence, the \(t\)-test showed no statistically significant difference in the operating speed between road sections with and without emergency lanes. However, this result must be interpreted with caution due to the extremely small sample size in the group without emergency lanes, which included only one road segment. The analysis of categorical variables via ANOVA did not reveal statistically significant differences in operating speed for speed limit, lane width, design speed, or terrain type, though terrain type approached statistical significance for both lanes (\(p=0.0970\) for the left land; \(p=0.1172\) for the right). Tukey-Kramer post hoc testing suggested higher speeds on flat terrain compared to hilly or mountainous terrain, but these differences were not statistically significant at the 0.05 level. Nonetheless, the consistent trend suggests a potential practical relevance worth exploring further in future research. In summary, the results for dual-carriageway road tangents indicate that traffic-related variables, particularly traffic flow density and ASDT, are the most influential factors affecting the operating speed. These effects are more pronounced in the left lane, likely due to its function in overtaking maneuvers. While the geometric characteristics and infrastructure features did not show strong statistical relationships in this dataset, their influence may become clearer with a larger and more diverse sample. Future studies should continue to examine the interaction between traffic flow dynamics and road design elements, especially in multilane settings where lane function varies. An important consideration arising from both analyses is the overall weak association between the operating speed and most investigated factors. This pattern suggests that factors beyond road geometry and traffic flow characteristics may exert a stronger influence on driver speed choice in these contexts. One plausible explanation is the absence of strong physical constraints on speed, such as those present on horizontal curves (e.g., curve radius and therefore centrifugal force). Tangents offer relatively unobstructed sight distances and driving comfort, enabling drivers to travel at speeds of their choosing with limited immediate feedback or correction imposed by the road itself. Moreover, the research was conducted on road segments outside urban areas, where default speed limits apply (typically 90 km/h for single-carriageway roads) unless otherwise posted. In such zones, in contrast to urban areas, enforcement intensity is generally lower, and penalties for speeding are comparatively lenient, particularly for marginal excesses over the posted speed limit. Additionally, Croatian legislation [57] include a legally recognized tolerance margin of 10 km/h for speed limits up to 100 km/h, and 10% for limits above 100 km/h. This means that a driver traveling at 100 km/h in a 90 km/h zone, or at 143 km/h on a motorway with a 130 km/h limit, is not considered to be speeding. This regulatory structure likely reduces the perceived risk of enforcement and diminishes the drivers' motivation to strictly adhere to speed limits on these segments. This interpretation is further supported by the findings of the Tukey-Kramer post hoc tests, which revealed no statistically significant differences in the operating speed across different posted speed limit categories for both single- and dual-carriageway road tangents (Figure 22). Such results underscore the salience of driver psychology and enforcement perception as determinants of actual driving behavior. On many roads where the measurements were taken, fixed speed enforcement is absent and its position is likely well known through public mapping platforms (like Google Maps), allowing drivers to adjust their behavior accordingly when appearing closer to the location of enforcement.