Técnicas como a harmonização da velocidade procuram gerir e controlar o tráfego com base nas condições de tráfego das rodovias em tempo real. A harmonização da velocidade utiliza limites de velocidade variáveis (L.V.V.) para fornecer aos condutores uma velocidade de operação mais apropriada, normalmente inferior ao limite de velocidade estático indicado, em resposta as condições dinâmicas das vias. O L.V.V. tem demonstrado capacidade de melhorar a mobilidade e a segurança nas rodovias. Com isso, modelos de avaliação de risco de colisão em tempo real são frequentemente adotados para quantificar os riscos de ocorrência de colisões em estudos de implantação do L.V.V. Na maioria dos estudos sobre L.V.V., modelos de probabilidade de colisão são adotados apenas para mensurar o desempenho do sistema. Estes algoritmos de controle de L.V.V. não levam em conta o risco de colisões em períodos futuros, e assim não usam impactos do L.V.V. para escolher o plano de controle com relação à segurança. No Brasil, estratégias de harmonização da velocidade não são empregadas. Como as condições de tráfego nas rodovias brasileiras não são homogêneas, e cada faixa de tráfego normalmente possui médias de velocidades, intensidades de fluxo e composições de tráfego diferentes, técnicas como o L.V.V Podem oferecer benefícios ao harmonizar as velocidades entre as faixas e assim retardar o aparecimento de congestionamentos, reduzir o número de ultrapassagens e o risco de colisões. Dessa forma, este trabalho busca avaliar a relação entre as características do tráfego e a probabilidade de ocorrer conflitos entre veículos, para assim desenvolver um modelo matemático capaz de expressar tal relação – usando como estudo de caso um trecho da rodovia BR-290/RS, situada na região metropolitana da cidade de Porto Alegre. Este modelo matemático alimenta um algoritmo L.V.V., empregado em um micro simulador de tráfego, para controlar o tráfego com o objetivo de aumentar a segurança. Resultados indicam que o modelo proposto classificou corretamente 87% dos conflitos efetivamente ocorridos em campo. Os resultados de simulação indicam que o emprego do sistema L.V.V. contribuiu significativamente para a redução da probabilidade de conflitos. Ainda, o L.V.V. aumentou as velocidades médias nos períodos de fluxo elevado, e também reduziu o desvio padrão das velocidades – oferecendo um tráfego mais homogêneo – que contribui para a redução do número de trocas de faixa e, consequentemente, para um aumento da segurança. / Techniques such as speed harmonization seek to manage and control traffic based on road traffic conditions in real time. Speed harmonization uses variable speed limits (VSL) to provide drivers with a more appropriate speed, usually below the stated static speed limit, in response to dynamic road conditions. The VSL has demonstrated its ability to improve mobility and road safety. Thus, real-time collision risk assessment models are often adopted to quantify the risk of collisions occurring in VSL implantation studies. In most VSL studies, collision probability models are utilized only to measure the system performance. These VSL control algorithms do not take into account the risk of collisions in future periods, and thus do not use the VSL impacts to choose the control plan concerning safety. In Brazil, Speed harmonization strategies are not employed yet. As the traffic conditions on Brazilian highways are not homogeneous, and each traffic range usually has different average speeds, flow intensities, and traffic compositions, VSL techniques can offer benefits by harmonizing speeds between lanes, slowing down congestion, reducing the number of overtaking and the risk of collisions.( Continue) Thus, this work seeks to evaluate the relationship between traffic characteristics and the probability of conflicts between vehicles, in order to develop a mathematical model capable of expressing such a relation - using as a case the BR-290/RS freeway, located in the Porto Alegre metropolitan area. This mathematical model will then feed a VSL algorithm, employed in a micro traffic simulator, to control traffic and increase safety. Results indicate that the proposed model correctly classified 87% of the conflicts actually occurred in the field. The simulation results indicate that the VSL contributed significantly to reducing the conflicts likelihood. Even more, the VSL increased the average speeds for high flow periods, and also reduced the standard deviation of speeds - offering a more homogeneous traffic - which contributes for reduction in the number of lane changes and, consequently, to an increase in safety.

Neste trabalho é apresentado um modelo de sistema de gestão da segurança no trânsito urbano, denominado SEGTRANS, que visa a redução dos acidentes de trânsito e a minimização dos conflitos de tráfego, com conseqüente aumento da segurança e do conforto para os usuários. O SEGTRANS contempla a organização de um banco de dados com informações sobre acidentes, conflitos de tráfego, sistema viário e zoneamento urbano, em programas de planilha eletrônica e sistema de informações geográficas; o desenvolvimento de técnica mista de avaliação da segurança viária com dados de acidentes, conflitos de tráfego e meio ambiente viário; o tratamento dos dados com a produção de relatórios e mapas temáticos; a sistemática para a definição das ações a serem implementadas visando reduzir os acidentes; e o processo de avaliação das medidas adotadas. Alguns dos principais estudos desenvolvidos no trabalho foram: definição da técnica de conflitos de tráfego, seleção das variáveis e formação do banco de dados de acidentes com montagem de programa em Access para introdução dos dados, técnica mista de avaliação da segurança viária, técnica de avaliação por carro teste e caminhada teste e tratamento dos dados em programas de planilha eletrônica e sistema de informação geográfica. / This work presents a model of management system for urban traffic safety, denominated SEGTRANS, which seeks the reduction of traffic accidents and the reduction of traffic conflicts, with consequent increase of safety and comfort for the users. The SEGTRANS contemplates the organisation of a database with information on accidents, traffic conflicts, road system and urban zoning, in electronic spreadsheet programs and geographic information systems; a development of a mixed technique of evaluation of the road safety with data of accidents, traffic conflicts and road environment; a treatment of the data with the production of reports and thematic maps; system for definition of actions to be implemented seeking to reduce the accidents; and a process of evaluation of the adopted measures. Some of the main studies developed in this work included: definition of the traffic conflict technique, selection of variables and formation of a database of accidents with program assembly in Access for introduction of data, a mixed technique of evaluation of the road safety, an evaluation technique for car test and walking test and treatment of data in electronic spreadsheet programs and geographic information systems.

Neste trabalho é apresentado um modelo de sistema de gestão da segurança no trânsito urbano, denominado SEGTRANS, que visa a redução dos acidentes de trânsito e a minimização dos conflitos de tráfego, com conseqüente aumento da segurança e do conforto para os usuários. O SEGTRANS contempla a organização de um banco de dados com informações sobre acidentes, conflitos de tráfego, sistema viário e zoneamento urbano, em programas de planilha eletrônica e sistema de informações geográficas; o desenvolvimento de técnica mista de avaliação da segurança viária com dados de acidentes, conflitos de tráfego e meio ambiente viário; o tratamento dos dados com a produção de relatórios e mapas temáticos; a sistemática para a definição das ações a serem implementadas visando reduzir os acidentes; e o processo de avaliação das medidas adotadas. Alguns dos principais estudos desenvolvidos no trabalho foram: definição da técnica de conflitos de tráfego, seleção das variáveis e formação do banco de dados de acidentes com montagem de programa em Access para introdução dos dados, técnica mista de avaliação da segurança viária, técnica de avaliação por carro teste e caminhada teste e tratamento dos dados em programas de planilha eletrônica e sistema de informação geográfica. / This work presents a model of management system for urban traffic safety, denominated SEGTRANS, which seeks the reduction of traffic accidents and the reduction of traffic conflicts, with consequent increase of safety and comfort for the users. The SEGTRANS contemplates the organisation of a database with information on accidents, traffic conflicts, road system and urban zoning, in electronic spreadsheet programs and geographic information systems; a development of a mixed technique of evaluation of the road safety with data of accidents, traffic conflicts and road environment; a treatment of the data with the production of reports and thematic maps; system for definition of actions to be implemented seeking to reduce the accidents; and a process of evaluation of the adopted measures. Some of the main studies developed in this work included: definition of the traffic conflict technique, selection of variables and formation of a database of accidents with program assembly in Access for introduction of data, a mixed technique of evaluation of the road safety, an evaluation technique for car test and walking test and treatment of data in electronic spreadsheet programs and geographic information systems.

Accidents are a complex process involving many contributory factors. The understanding of the accident process has often been sought by the use of accident data. Although accident data provide a direct relationship to estimating accident risk, there are many drawbacks associated with the use of these data. The major drawback with the use of accident data is the very fact that traffic engineers have to wait for accidents to occur before any interventions can be made. This alone is significant as the time span required to collect a sample size is often a three-year period. The many deficiencies with accident data have led to alternative measures such as traffic conflict techniques (TCT's) to estimate accident risk.In this investigation. traffic conflict techniques were used to estimate accident risk. There are four basic traffic conflict concepts and the development of these techniques was based on the accident process. The aim of this investigation was to highlight the differences between these concepts and to assess the applicability of these concepts to vehicle-pedestrian conflicts. The investigation was based on applying the various conflict techniques to data obtained at three intersections in the Durban CBD. In order to record the data an innovative method of using digital imaging was employed. This led to the development of a computer program to analyse conflict events. Analysis of the intersections based on the conflict techniques indicates that the intersections of Pine-Field and Commercial-Grey have a high probability of road users being involved in a "serious event" once there is an interaction between them. However, the probability for Commercial-Albert intersection is low thus indicating a safe intersection for vehicle-pedestrian interactions. The number of "serious events" at these locations was found to be related to the interacting traffic volumes - the conflict rate increases with increasing traffic volume. The use of conflict-volume models and accident models together with the conflict concepts agree that the accident risk is related to the conflicting traffic volumes and speed of the road users. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

This work deals with the and preemptive road users behaviour safety analysis problem. Safety analysis is based on a processing of road users trajectories obtained from processed aerial videos captured by drons. A system for traffic conflicts detection from spatial-temporal data is presented in this work. The standard approach for pro-active traffic conflict indicators evaluation was extended by simulating traffic objects movement in the scene using Ackerman steering geometry in order to get more accurate results.

A before-and-after analysis was performed at eleven intersections where a bike box was installed in Portland, Oregon to explore the safety effects of the treatment. Video data were gathered prior to installation at 14 intersections where a bike box installation was planned by the Portland Bureau of Transportation. Cameras were set up to capture three full twenty-four hour days (72 hours) of data for each intersection from Tuesday through Thursday. Of the 14 original selected intersections, 11 intersections actually received the bike box treatment. Video data were again gathered for these intersections after the installation of the bike box for another three full twenty-four hour days (72 hours) between Tuesday and Thursday. One day of data (24 hours) was selected for observation from both the before and after periods in the analysis for each study intersection during midweek. Safety effects were evaluated by three metrics: 1) observed conflicts; 2) observed cyclist behavior for all conflicts as measured by head or shoulder checks; and 3) reported crash data. To develop the conflict data, a log was created of each motor vehicle and bicycle passing through the intersection for approximately 528 hours of video. All conflicts that were observed during the period were further reviewed by an expert panel that scored conflicts by severity. Following this review, a total of 18 conflicts were observed during the before period. The total exposure in the before period was 39,497 motor vehicles in the vehicle lane adjacent to the bike lane (10,454 of which were right-turning) and 7,849 bicycles. A total of 19 conflicts were observed during the after period. Total exposure was 42,381 motor vehicles in the vehicle lane adjacent to the bike lane (11,053 of which were right-turning) and 5,852 bicycles. The sample size of observed conflicts was insufficient to draw statistically significant conclusions for any of the specific intersections that were treated. When taking in account the total amount of conflicts, the limited data suggest a slight increase in the rate of conflicts when normalized against a product of right-turning vehicles and bicycles observed in the intersection. The data also suggest that the installation of a bike box at an intersection reduces the rate of conflicts per hundred motor vehicles and increases the rate of conflicts per hundred bicyclists. Data regarding head-checks from the bicyclist shows an increase in bicyclists observing the possibility of conflicts approaching from behind as they pass through the intersection. A review or crash data at each of the intersections shows an increase at three of the observed intersections and a decrease at the remaining five.

<p><a>Proactive evaluation of road safety is one of the most important objectives of transportation engineers. While current practice typically relies on crash-based analysis after the fact to diagnose safety problems and provide corrective countermeasures on roads, surrogate measures of safety are emerging as a complementary evaluation that can allow engineers to proactively respond to safety issues. These surrogate measures attempt to address the primary limitations of crash data, which include underreporting, lack of reliable insight into the events leading to the crash, and long data collection times. </a></p> <p>Traffic conflicts are one of the most widely adopted surrogate measures of safety because they meet the following two conditions for crash surrogacy: (1) they are non-crash events that can be physically related in a predictable and reliable way to crashes, and (2) there is a potential for bridging crash frequency and severity with traffic conflicts. However, three primary issues were identified in the literature that need to be resolved for the practical application of conflicts: (1) the lack of consistency in the definition of traffic conflict, (2) the predictive validity from such events, and (3) the adequacy of traffic conflict observations.</p> <p>Tarko (2018) developed a theoretical framework in response to the first two issues and defined traffic conflicts using counterfactual theory as events where the lack of timely responses from drivers or road users can produce crashes if there is no evasive action. The author further introduced a failure-based definition to emphasize conflicts as an undesirable condition that needs to be corrected to avoid a crash. In this case, the probability of a crash, given failure, depends on the response delay. The distribution of this delay is adjusted, and the probability is estimated using the fitted distribution. As this formal theory addresses the first two issues, a complete framework for the proper identification of conflicts needs to be investigated in line with the failure mechanism proposed in this theory.</p> <p>The objective of this dissertation, in response to the third issue, is to provide a generalized framework for proper identification of traffic conflicts by considering the failure-based definition of traffic conflicts. The framework introduced in this dissertation is built upon an empirical evaluation of the methods applied to identify traffic conflicts from naturalistic driving studies and video-based tracking systems. This dissertation aimed to prove the practicality of the framework for proactive safety evaluation using emerging technologies from in-vehicle and roadside instrumentation.</p> <p>Two conditions must be met to properly claim observed traffic events as traffic conflicts: (1) analysis of longitudinal and lateral acceleration profiles for identification of response due to failure and (2) estimation of the time-to-collision as the period between the end of the evasion and the hypothetical collision. Extrapolating user behavior in the counterfactual scenario of no evasion is applied for identifying the hypothetical collision point.</p> <p>The results from the SHRP2 study were particularly encouraging, where the appropriate identification of traffic conflicts resulted in the estimation of an expected number of crashes similar to the number reported in the study. The results also met the theoretical postulates including stabilization of the estimated crashes at lower proximity values and Lomax-distributed response delays. In terms of area-wide tracking systems, the framework was successful in identifying and removing failure-free encounters from the In-Depth understanding of accident causation for Vulnerable road users (InDeV) program.</p> <p>This dissertation also extended the application of traffic conflicts technique by considering estimation of the severity of a hypothetical crash given that a conflict occurs. This component is important in order for conflicts to resemble the practical applications of crashes, including the diagnostics of hazardous locations and evaluating the effectiveness of the countermeasures. Countermeasures should not only reduce the number of conflicts but also the risk of crash given the conflict. Severity analysis identifies the environmental, road, driver, and pre-crash conditions that increase the likelihood of severe impacts. Using dynamic characterization of crash events, this dissertation structured a probability model to evaluate crash reporting and its associated severity. Multinomial logistic models were applied in the estimation; and quasi-complete separation in logistic regression was addressed by providing a Bayesian estimation of these models.</p>