Further Evaluation of the Relationship between Enhanced Consistency Model and Safety of TwoLane Rural Roads in Israel and Germany

Mattar-Habib, Caroline; Polus, Abishai; Farah, Haneen · 2008 · DOAJ

DOI: 10.18757/ejtir.2008.8.4.3360

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Summary

This study investigates the relationship between road design consistency and crash probability on two-lane rural highways, addressing the limitation of existing models that primarily focus on horizontal alignment in level terrain. The authors hypothesize that speed inconsistency, driven by variations in both horizontal and vertical geometric features, contributes significantly to crash risk, particularly in hilly regions where truck performance differs markedly from passenger cars. The research aims to validate an enhanced consistency model that incorporates vertical alignment and heavy vehicle dynamics, testing its predictive power using data from Israel and Germany. The methodology utilizes an enhanced integrated-consistency model calculated via the Highway Speed Profile and Consistency (HSPC) software. This model estimates consistency based on three parameters: the normalized area bounded by the car speed profile and average speed, the standard deviation of car speeds, and the normalized area bounded between the speed profiles of cars and trucks. Data were collected from 26 road segments in northern Israel (crash data from 1997–2001) and 83 segments in Saxony, Germany (crash data from 2003–2005). The analysis included only crashes involving casualties. Poisson regression models were employed to relate crash frequency to road consistency, traffic volume (AADT), and segment length, accounting for the discrete and rare nature of crash events. The results demonstrate a statistically significant negative relationship between road consistency and crash numbers in both countries. As consistency scores increase, the estimated average number of crashes per year decreases. The calibrated Poisson models for Israel and Germany showed similar trends, with consistency coefficients of -0.228 and -0.144, respectively. Traffic volume and segment length were also significant predictors; notably, the elasticity of accidents with respect to traffic volume was greater than 1 in Israel and less than 1 in Germany. The models fit the data adequately after adjusting for underdispersion in the German dataset. The similarity in model trends is attributed to comparable driver age distributions and vehicle ages, despite differences in roadside infrastructure such as narrow shoulders in Germany and pavement quality in Israel. The significance of this work lies in providing a validated tool for highway planners to assess safety during the design phase. By using the enhanced consistency model and HSPC software, engineers can identify design deficiencies related to speed variability and vehicle performance differences before construction. This approach allows for the modification of geometric designs to improve consistency, thereby enhancing safety levels and potentially saving lives on two-lane rural roads, particularly in complex terrains where traditional consistency measures are insufficient.

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• Empirical Findings: crash risk outcomes