Identification of road horizontal alignment inconsistencies – a pilot study from the czech republic

Ambros, Jiří; Valentová, Veronika · 2016 · Crossref

DOI: 10.3846/bjrbe.2016.07

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Summary

This pilot study addresses the safety risks associated with inappropriate speed on Czech rural roads, particularly regarding horizontal alignment inconsistencies. The research was motivated by police data indicating that over one-third of road fatalities in the Czech Republic are linked to horizontal curve accidents, with inappropriate speed being the primary cause in 66% of these cases. The authors aimed to demonstrate the practical application of alignment consistency evaluation—a measure of how well road geometry coordinates to avoid critical driving maneuvers—on historical rural roads lacking precise design data. The study sought to validate this approach using low-cost technology, investigate the relationship between consistency measures and actual safety, and propose steps for implementation by road agencies. The researchers conducted data collection on a 2.5 km section of a historical rural road (Road III/3846) near Brno, consisting of three straight segments and three curves. They utilized a low-cost Holux M-1000C Bluetooth GPS logger placed in a personal vehicle, recording position data every second during fifteen trips. Due to the absence of design documentation, the authors developed a method to determine the central trajectory and segment the road into straight and curve elements using cumulative angle calculations and curvature change rates (CCR). They calculated consistency levels based on the difference in CCR and the 85th percentile operating speed ($V_{85}$) between consecutive segments, classifying them as "good," "fair," or "poor" according to established thresholds. The results identified one curve as having "fair" consistency, characterized by a significant speed reduction and high curvature change rate, while the other two curves were classified as "good." An illustrative speed model derived from the data showed a significant negative linear relationship between CCR and $V_{85}$. Validation against police accident records from 1998–2013 revealed that the "fair" consistency curve had a significantly higher accident rate (12.1 veh⁻¹·day⁻¹·m⁻¹·year⁻¹) compared to the "good" curves (approximately 3.7–4.2). The ratio of accident rates between the "good" and "fair" segments was approximately 1:3, confirming that lower alignment consistency correlates with higher safety risks. The study concludes that alignment consistency levels can serve as effective indirect road safety indicators, allowing for proactive identification of hazardous road segments without waiting for accident occurrences. This approach supports the development of "self-explaining roads" where geometry aligns with driver expectations. While the pilot demonstrated the feasibility of using low-cost GPS technology for this purpose, the authors acknowledge limitations regarding GPS accuracy and sample size. They recommend future studies expand to larger road networks, automate the calculation procedures, and incorporate additional variables to refine speed prediction models.

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• road geometry