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Category : Electronic books
Languages : en
Pages : 61
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Book Description
Continued emphasis on active transportation has led to a proliferation of vulnerable road users (VRUs) such as bicyclists and pedestrians at intersections. Intersections are critical locations as many crashes occur due to mixed traffic flow and various conflicting patterns between road users. Intersection safety has primarily relied on historical crash data. However, due to several limitations including unpredictability and irregularity of occurrence of crashes in real environment, quantitative and qualitative determination of crashes may not be accurate. This study explores alternative measures to the traditional safety analysis known as surrogate safety measures (SSMs). SSMs such as Time to Collision (TTC), Post Encroachment Time (PET) and a variant of TTC, Relative Time to Collision (RTTC) were used to evaluate safety at ten signalized intersections in the city of San Diego. The analysis was conducted in two main parts: proactive safety evaluation for VRUs at signalized intersections by comparison of SSMs and predicting critical bicycle-vehicle conflicts at signalized intersections. In part one, frequency of each SSMs was estimated to identify critical intersections for VRUs and then a comparative study of each SSMs were conducted. It was found that RTTC alone was insufficient to accurately identify critical conflicts. Furthermore, safety evaluation results showed that a single SSM was not reliable but a combination of different SSMs was necessary to ensure the reliability of evaluations. In part two, logistic regression model was developed in R to predict critical conflicts based on PET measure. Bicycle-vehicle kinematics data were monitored for certain period before predicting critical conflicts. Several scenarios were analyzed considering different combinations of PET threshold value and monitoring period, and it was found that a scenario with PET threshold value of 3s and monitoring period of 2s led to the best model based on its statistical performance. Of the many input variables investigated, velocity of the conflicting objects and minimum relative approach velocity were found to be statistically more significant. The model was tested under two cases; sensitivity maximization and maximum overall accuracy, and it was found that sensitivity maximization was more suitable as it ensured accurate prediction of critical conflicts.
Author:
Publisher:
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Category : Electronic books
Languages : en
Pages : 61
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Book Description
Continued emphasis on active transportation has led to a proliferation of vulnerable road users (VRUs) such as bicyclists and pedestrians at intersections. Intersections are critical locations as many crashes occur due to mixed traffic flow and various conflicting patterns between road users. Intersection safety has primarily relied on historical crash data. However, due to several limitations including unpredictability and irregularity of occurrence of crashes in real environment, quantitative and qualitative determination of crashes may not be accurate. This study explores alternative measures to the traditional safety analysis known as surrogate safety measures (SSMs). SSMs such as Time to Collision (TTC), Post Encroachment Time (PET) and a variant of TTC, Relative Time to Collision (RTTC) were used to evaluate safety at ten signalized intersections in the city of San Diego. The analysis was conducted in two main parts: proactive safety evaluation for VRUs at signalized intersections by comparison of SSMs and predicting critical bicycle-vehicle conflicts at signalized intersections. In part one, frequency of each SSMs was estimated to identify critical intersections for VRUs and then a comparative study of each SSMs were conducted. It was found that RTTC alone was insufficient to accurately identify critical conflicts. Furthermore, safety evaluation results showed that a single SSM was not reliable but a combination of different SSMs was necessary to ensure the reliability of evaluations. In part two, logistic regression model was developed in R to predict critical conflicts based on PET measure. Bicycle-vehicle kinematics data were monitored for certain period before predicting critical conflicts. Several scenarios were analyzed considering different combinations of PET threshold value and monitoring period, and it was found that a scenario with PET threshold value of 3s and monitoring period of 2s led to the best model based on its statistical performance. Of the many input variables investigated, velocity of the conflicting objects and minimum relative approach velocity were found to be statistically more significant. The model was tested under two cases; sensitivity maximization and maximum overall accuracy, and it was found that sensitivity maximization was more suitable as it ensured accurate prediction of critical conflicts.
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Category : Electronic books
Languages : en
Pages : 41
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The goal of this dissertation is to develop a vision-based system to evaluate risk scores of roadway intersections where frequent interactions of pedestrians and bicyclists with motorized traffic exist. The research outcome is valuable for preventing traffic incidents involving pedestrians or bicyclists, which are becoming a significant concern in urban areas. This research focuses on vehicle-pedestrian and vehicle-bicycle conflicts at signalized intersections. Multi-way video sequences were collected at several intersections in the City of San Diego, and computer vision algorithms, including object detection (Faster-R-CNN) and visual tracking (KCF), were developed to extract trajectory data of vehicles or pedestrians in videos. Learning-based 3D localization method was introduced to get rid of the perspective effect and further improve the usability and accuracy of trajectory data. These visual perception results are used in safety surrogate analysis to proactively evaluate safety at intersections. Results with comparative studies suggest the proposed algorithm can significantly improve localization accuracy, especially when using noisy video data, and result in improved safety measures.
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Category : Electronic book
Languages : en
Pages :
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Author: Raghavan Srinivasan
Publisher: Transportation Research Board
ISBN: 0309213452
Category : Technology & Engineering
Languages : en
Pages : 48
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Book Description
TRB’s National Cooperative Highway Research Program (NCHRP) Report 705: Evaluation of Safety Strategies at Signalized Intersections explores crash modification factors (CMFs) for safety strategies at signalized intersections. CMFs are a tool for quickly estimating the impact of safety improvements.
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Category :
Languages : en
Pages :
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Author: Sohail Zangenehpour
Publisher:
ISBN:
Category :
Languages : en
Pages :
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"Pedestrians and cyclists are amongst the most vulnerable road users as their accidents involving motor vehicles result in high injury and fatality rates for these two modes. Data collection for non-motorized road users remains a challenge and automated data collection methods are far more advanced for motorized traffic. To improve cyclist safety and promote urban cycling, cities have been building bicycle infrastructure, such as cycle tracks and bicycle boxes. These facilities have been built and expanded but due to the lack of appropriate data and problems with automated cyclist data collection, very little in-depth research has been carried out to investigate the safety impacts of these infrastructures. The majority of non-motorized safety studies are based on traditional methods which use observed accident and injury data. An important shortcoming of this approach is the need to wait for accidents to occur over several years. An alternative to traditional safety analysis is surrogate safety methods which can provide statistically sufficient data in a shorter time period. However, to perform surrogate safety studies, microscopic data from road users is needed. To address the shortcomings of the current literature and to improve the microscopic data collection tools for non-motorized road users, this thesis presents an automated methodology to classify road users in traffic videos - this methodology is complementary to existing object-tracking tools. The methodology is tested and validated using a large dataset from signalized intersections with high mixed traffic in Montreal, Canada. Road users are classified into three main categories: pedestrian, cyclist, and motor vehicle, with an overall accuracy of over 95 %. The proposed methodology is capable not only of counting the movements of the different road users (generating exposure measures), but also provides microscopic data separately for each road user type for safety analysis. As a result, performing automated surrogate safety studies becomes possible for facilities with mixed motorized and non-motorized traffic. As part of this thesis, the relationship between the surrogate safety measure used in this research, post encroachment time, and the historical accident data has been investigated and shows promising correlation. Using several hours of video recorded from a sample of signalized intersections in Montreal, and analyzed using the proposed techniques, the safety effects of two types of bicycle infrastructure, cycle tracks and bicycle boxes, have been investigated. The results show that based on the interactions between cyclists and turning vehicles, having a cycle track on the right side of the road is safer than not having a cycle track or than having a cycle track on the left side of the road. Also the study on the safety of bicycle boxes at intersections reveals that this type of bicycle facility is associated with a significant reduction in the severity of interactions (increase in post encroachment time) between cyclists and vehicles." --
Author: Raghavan Srinivasan (Transportation engineer)
Publisher:
ISBN:
Category :
Languages : en
Pages : 38
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Book Description
"TRB's National Cooperative Highway Research Program (NCHRP) Report 705: Evaluation of Safety Strategies at Signalized Intersections explores crash modification factors (CMFs) for safety strategies at signalized intersections. CMFs are a tool for quickly estimating the impact of safety improvements"--Publisher's description.
Author: Young-Jun Kweon
Publisher:
ISBN:
Category : Roads
Languages : en
Pages : 86
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Book Description
This research was undertaken to develop an evaluation procedure to identify high-risk four-legged signalized intersections in VDOT's Northern Virginia district by traffic movements and times of day. By using the developed procedure, traffic engineers are expected to be able to identify signalized intersections where the traffic crash occurrences under different traffic conditions for different times of day are more frequent than would normally be expected. Using generalized linear models such as negative binomial models, one safety performance function was estimated for each of nine crash population reference groups formed by three traffic crash patterns (crash patterns 1, 4, and 6) and four times of day (A.M. peak, mid day, P.M. peak, and evening off peak). Crash pattern 1 is a same-direction crash (rear-end, sideswipe or angle crash) that occurs after exiting the intersection; crash pattern 4 is a right-angle crash between two adjacent straight-through vehicle movements in the intersection; and crash pattern 6 is an angle or head-on or opposite sideswipe crash between a straight-through vehicle movement and an opposing left-turn vehicle movement in the intersection. The procedure developed in this study is based on the empirical Bayes (EB) method. Additional data do not need to be collected in order to use the EB procedure because all the data required for applying the EB procedure should be obtainable from VDOT's crash database and from Synchro input data that are already available to traffic engineers for traffic signal phase plans. Thus, the EB procedure is cost-effective and readily applicable. For easy application of the EB procedure, an EB spreadsheet was developed using Microsoft Excel, and a users' guide was prepared. These are available from the author upon request.
Author: Thanh Le (Highway engineer)
Publisher:
ISBN:
Category : Road markings
Languages : en
Pages : 92
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Book Description
Evaluates multiple low-cost safety improvements at signalized intersections for bacis signing, pavement marking, and signal enhancements.
Author: Raghavan Srinivasan
Publisher:
ISBN:
Category : Roads—Interchanges and intersections
Languages : en
Pages : 56
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Book Description
This study evaluated the safety effect of the flashing yellow arrow (FYA) treatment at signalized intersections. The major objective of this strategy is to reduce the frequency of left-turn (LT) crashes, especially those that involve a collision between left turns and vehicles traveling straight through from the opposite direction. The project team conducted an empirical Bayes before-after analysis of installations in Nevada, North Carolina, Oklahoma, and Oregon. The treatments were divided into seven categories depending on the phasing system in the before and after periods, number of roads where FYAs were implemented, and number of legs at each intersection. The first five categories involved permissive or protected-permissive phasing in the before period. Intersections in these five treatment categories experienced a reduction in the primary target crashes under consideration: LT crashes and left-turn-with-opposing-through (LTOT) crashes at the intersection level. The reduction ranged from 15 to 50 percent depending on the treatment category. Intersections in categories 6 and 7 had at least one protected LT phase in the before period, and after phasing had an FYA protected-permissive LT phase without time-of-day operation (category 6) and with time-of-day operation (category 7). Consistent with results from previous studies, these intersections experienced an increase in LT and LTOT crashes. The B/C ratios for categories 1-5 ranged from 56:1 to 144:1.
