Search

A microscopic gap acceptance model is presented that simulates overtaking behavior on two-lane highways. The decision to initiate overtaking is expressed as a function of each driver's perception of the expected time-to- collision (TTC) with the nearest opposing vehicle at the end of maneuver. The available gap is accepted if the driver's perception of TTC exceeds a predetermined threshold for safe return (critical TTC). The gap acceptance model is calibrated and validated based on overtaking video-recording data for a two-lane highway. The overtaking gap acceptance model is then compared, for consistency and transferability, with independent aggregate field data, as well as with two other simulation models and values given in the Highway Capacity Manual for similar two-lane highways. The gap acceptance simulation demonstrated that the proposed overtaking model is able to provide reliable measures of traffic attributes for two-lane highway operation, as verified experimentally. Key words: two-lane highways, overtaking, gap acceptance. Dans le cadre de cette etude, on presente un modele microscopique d'acceptation d'espacement qui simule le comportement de depassement sur les routes a deux voies. La decision d'entreprendre un depassement est exprimee en fonction de la perception de chaque conducteur du temps avant une collision (TAC) avec le vehicule oppose le plus pres, et ce, a la fin de la manoeuvre. L'espacement disponible est accepte si la perception qu'a le conducteur du TAC excede un seuil preetabli du retour sans accident (TAC critique). On calibre et valide le modele d'acceptation de l'espacement en fonction des donnees d'enregistrement video de depassements sur une route a deux voies. On compare ensuite le modele d'acceptation d'espacement de depassement, aux fins de coherence et de transferabilite, aux donnees de terrain independantes et globales, ainsi qu'a deux autres modeles de simulation et aux valeurs fournies dans le 'Highway Capacity Manual' en rapport avec des routes a deux voies semblables. La simulation d'acceptation d'espacement a demontre que le modele de depassement propose peut fournir des mesures fiables des attributs de la circulation aux fins de l'exploitation par voie sur les routes a deux voies, tel que verifie experimentalement. [Traduit par la Redaction] Mots-cles: routes a deux voies, depassement, acceptation d'espacement., Introduction In recent years, microscopic simulation models have gained increased acceptance as reliable investigative tools for understanding traffic operations and evaluating safety performance. Despite this trend, the development and application [...]

Large speed differentials between highway segments are associated with an increase in the number of accidents. Traditional speed differential measures, derived from single-level linear regression models, suffer from serious deficiencies, namely underestimating the speed differential (due to intracorrelated data) and inflating the adequacy of the model's explanation (due to aggregate data). High-quality speed differentia] predictions are highly desirable right from the initial design phase, but the estimation process is not straightforward, and decision makers must recognize that speed differential predictions are subject to considerable uncertainty. This paper compares four models; two single-level models, a conventional multilevel model, and a Bayes multilevel model. The results show empirically that multilevel models increase the accuracy and precision of estimates of speed differentials, possibly with fewer data. The paper introduces a new, easy to interpret speed consistency measure that simply represents the probability that a vehicle exceeds a certain speed differential. This measure is calculated using a multilevel model and takes into account the uncertainty in the estimates of speed differentials. Overall, we show that a multilevel modeling approach can improve the quality of decision making that makes use of speed differential information in road design and road safety. Key words: speed, highway safety, statistical models, road design. Les grands differentiels de vitesse entre des troncons d'autoroute sont relies a une augmentation du nombre d'accidents. Les mesures habituelles de mesure de la vitesse, derivees de modeles de regression lineaire a un niveau, presentent de graves manques : sous-estimation du differentiel de vitesse (en raison de l'intra-correlation des donnees) et l'exageration de la pertinence de Implication du modele (en raison des donnees globales). Il serait souhaitable d'avoir des previsions du differentiel de vitesse de grande qualite des la phase de conception initiale, mais le processus d'estimation n'est pas simple et les decideurs doivent reconnaitre que les previsions du differentiel de vitesse sont sujettes a une grande incertitude. Le present article compare quatre modeles : deux modeles a un niveau, un modele convenlionnel a plusieurs niveaux, et un modele de Bayes a plusieurs niveaux. Les resullais montrent de maniere empirique que les modeles a plusieurs niveaux augmentent l'exactirude et la precision des estimations des differentiels de vitesse, possiblement en utilisant moins de donnees. Cet article introduit une nouvelle mesure facile a interpreter de la Constance de la vitesse qui represente simplement la probability qu'un vehieule excede un certain differentiel de vitesses. Cette mesure est calculee en utilisant un modele a plusieurs niveaux et elle tient compte de l'incertitude dans les estimations des differentiels de vitesse. De maniere generate, nous montrons qu'une approche de modelisation a plusieurs niveaux peut ameliorer la qualite de la prise de decisions qui se servent des differentiels de vitesse lors de la conception des routes et pour la securite routiere. Mots-des : vitesse. securite routiere. modeles statistiques, conception routiere., [Traduit par la Redaction] Introduction The concepts of design speed and speed consistency are well established in the highway design process (Fitzpatrick et al. 2000; AASHTO 2004). Speed consistency is [...]

This paper applies a calibrated microscopic simulation model to assess the safety implications of signalization at a stop-controlled isolated intersection. Safety performance is measured in terms of a crash potential index (CPI) that makes use of time-specific vehicle parameters, such as deceleration rates, spacing, and speed profiles. Four performance measures are obtained: (i) average CPI/vehicle, (ii) CPI 85th percentile, (iii) number of vehicles with CPI > 0 (defined as interacting), and (iv) number of conflicts (defined in terms of a given CPI threshold). Two types of interactions are considered, namely rear end and angled. For rear-end interactions, CPI/vehicle was found to be significantly higher following the introduction of fixed signal controls. For angled interactions, CPI/vehicle was found to decrease with signalization. For both types of interactions, the CPI 85th percentile was found to decrease nonlinearly with signalization, especially for higher assumed volumes on the major approach. Rear-end vehicle interactions increased significantly following signalization and with increasing volume, whereas no such increase was observed for angled interactions. The key observation is that the number of vehicles subject to angled interactions was found to decrease after signalization. Key words: safety performance, microscopic simulation, signalized and stop-controlled intersections. Cet article applique un modele de simulation microscopique etalonne pour evaluer les implications de securite d'une signalisation a un carrefour isole controlee par un arret. Le rendement en matiere de securite est mesure en termes d'indice potentiel de collision (<< CPI >>) qui utilise des parametres temporels des vehicules tels que les taux de deceleration, l'espacement et les profils de vitesse. Quatre mesures du rendement ont ete obtenues : (i) CPI moyen par vehicule, (ii) 85e percentile du CPI, (iii) le nombre de vehicules ayant un CPI > 0 (definis comme interdependants), et (iv) le nombre de conflits (defini en termes d'un CPI seuil donne). Deux genres d'interactions sont consideres : par l'arriere et a angle. Le CPI/veh. pour les interactions par l'arriere s'est grandement accru apres l'introduction de controles de signaux fixes. Le CPI/veh. pour les interactions a angle diminuait avec la signalisation. Pour les deux types d'interactions, le 85e percentile du CPI diminuait de maniere non lineaire avec la signalisation, surtout pour les volumes de trafic presumes plus eleves dans l'approche majeure. Les interactions entre vehicules par l'arriere ont augmente considerablement apres la mise en place de la signalisation et avec un volume de trafic superieur; cette augmentation n'a pas ete observee pour les interactions a angle. L'observation principale est que le nombre de vehicules sujets a des interactions a angle a diminue apres la mise en place de la signalisation. Mots-cles : rendement en securite, simulation microscopique, carrefours signales et controles par un arret. [Traduit par la Redaction], Introduction A number of recent studies of crashes for North American urban roads suggest that over 50% of these reported crashes take place in proximity to intersections. Intersections present special [...]

Differential car/truck speed limits have been used to enhance road safety and increase the fuel efficiency of trucks. For two-lane highways, the safety of these differential speed controls could be affected by possible changes in the pattern of car and truck interactions and their associated crash risks, especially as it pertains to overtaking. In this paper, a microscopic simulation model is presented that assesses the safety and traffic implications of differential car/truck speed limits for two-lane highway operations, with emphasis on the overtaking maneuver. Three speed control strategies are considered: uniform posted speed limits (USLs), differential posted car-truck speed limits (DSLs), and differential mandated truck speed limits (MSLs). Mandated limits involve the use of on-board truck limiters or governors with preset maximum thresholds. The results from several simulation tests suggest that DSLs andMSLs reduce the average travel speed (ATS) of the traffic stream. DSL and MSL controls were found to slightly increase head-on time-to-collision (TTC) and percentage time spent following (PTSF). The total number of overtakes was found to increase slightly for DSL and MSL controls compared to USLs. While the number of car-truck overtakes increased significantly for DSLs andMSLs, the number of car-car overtakes resulted in a significant decrease. It was concluded that three measures of ATS, TTC, and car-car overtaking positively impacted safety, while PTSF, car-truck, and total number of overtakes negatively impacted safety because of differential speed limit controls. [ABSTRACT FROM AUTHOR]

Various countermeasures can be introduced to reduce collisions at highway–railway grade crossings. These countermeasures may take different forms, such as passive and (or) active driver warning devices, supplementary traffic controls (four quadrant barriers, wayside horn, closed circuit television (CCTV) monitoring, etc.), illumination, signage and highway speed limit, etc. In this research, we present a structured model that makes use of data mining techniques to estimate the effect of changes in countermeasures on the expected number of collisions at a given crossing. This model serves as a decision-support tool for the evaluation and development of cost-effective and practicable safety program at highway–railway grade crossings. The use of data mining techniques helps to resolve many of the problems associated with conventional statistical models used to predict the expected number of collisions for a given type of crossing. Statistical models introduce biases that limit their ability to fully represent the relationship between selected countermeasures and resultant collisions for a mix of crossing attributes. This paper makes use of Canadian inventory and collision data to illustrate the potential merits of the proposed model to provide decision support. [ABSTRACT FROM AUTHOR]