![]() ![]() They found that crash frequency increased with increasing acceleration lane length. identified the speed-change lanes as the influence areas. (1999) both used 3 years of crash data from 192 acceleration lanes in Washington to develop SPFs with the same variables. Bauer and Harwood (1998) and Bared et al. In spite of the importance of crash prediction modeling for freeway merge areas, only a few studies have been done. The basic premise in their underlying approach is that a change in traffic volume, geometry or operational characteristics at a site can result in a change in the surrogate measure (conflicts) but will not affect the crash–conflict relationship such a relationship, if it can be established with confidence, can then be used to estimate the change in crashes associated with a change in conflicts and, by inference, the safety effect of the change at the intersection. (2014) and Lorion and Persaud (2015) have demonstrated the promise of this approach in successfully developing and applying crash–conflict models (based on annual crashes and peak hour conflicts) for signalized intersections and unsignalized intersections, respectively, to evaluate the safety of alternate scenarios. In this, observed or simulated traffic conflicts, rather than historical collision data used in conventional SPFs, can be used as a surrogate safety measure to predict related crashes. Another approach that has been explored more recently, but for other site types, is based on surrogate safety measures ( Gettman et al. Conventional crash-based safety performance functions (SPFs) can in principle be estimated to determine the relationship between collisions and traffic volumes (such as annual average daily traffic (AADT), average daily traffic (ADT), and peak hour volume (PHV)), geometric features (length, lane configuration and ramp configuration), and (or) traffic control systems (with or without metering) and used for assessing the safety of ramp junctions under various design and operational scenarios. Merging movements and lane change maneuvers on freeways create turbulence and pose a high risk of collisions, so the safety of the ramp–freeway junctions is critical. Ceci suggère que l’approche de conflit de collision est une substitution raisonnable pour les modèles conventionnels de prédiction de collisions en matière d’évaluation des effets sur la sécurité dans le cas de changements de conception, particulièrement pour ces changements qui ne peuvent pas être capturés dans les modèles conventionnels. Les résultats des SPF fondés sur les conflits concordent avec ceux des SPF fondés sur les collisions développés pour le même échantillon, avec des coefficients logiquement négatifs pour la longueur de voie d’accélération et des coefficients positifs pour les volumes de trafic. Les SPF intégrant les conflits à l’origine de collisions avec les seuils de temps avant la collision ont été alors développés et comparés. Cette approche a été explorée en utilisant la micro simulation dans le but de produire et d’analyser des conflits pour les zones de convergence sur les autoroutes de l’Ontario. Une approche utilisant des mesures de sécurité de substitution peut régler cette question, pourvu que ces mesures puissent être liées aux collisions. Les fonctions de rendement en matière de sécurité (« SPF ») fondées sur les collisions ne peuvent typiquement pas tenir compte de tous les facteurs opérationnels et de conception qui contribuent à la fréquence des collisions dans l’évaluation des effets de ces facteurs sur la sécurité. This suggests that the crash–conflict approach is a reasonable substitute for conventional crash prediction models in assessing the safety effects of design changes, especially for those changes that cannot be captured in the conventional models. ![]() The results of the conflict-based SPFs are in agreement with those from crash-based SPFs developed for the same sample, with logically negative coefficients for acceleration lane length and positive coefficients for traffic volumes. Crash–conflict integrated SPFs with different time to collision thresholds were then developed and compared. This approach was explored by using microsimulation to generate and analyze conflicts for merge areas on Ontario freeways. An approach using surrogate safety measures can address this issue, providing these measures can be linked to crashes. Crash-based safety performance functions (SPFs) typically cannot account for all design and operational factors that contribute to crash frequency in assessing the safety impacts of these factors. ![]()
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