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Author: Meghna Chakraborty Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 206
Book Description
Evaluating the safety performance of roadway segments and intersections typically involves associating traffic crashes, injuries, and fatalities to various roadway and traffic characteristics, which typically vary broadly between rural and urban contexts. In rural areas, roadway geometric characteristics often play a critical role in the safety performance of a given roadway, while myriad other factors, including driveways and intersections, tend to have a greater influence on urban roadway safety. However, certain geometric aspects, such as the characteristics of the horizontal curvature and the impact of driveway land-use type have not been well-explored in prior roadway safety research. There has also been limited research on the safety performance for roadways of lower functional classifications, such as minor arterial and collector roadways, which comprise a substantial portion of the nationwide roadway network but are often designed to lower standards and possess driver and trip characteristics that typically differ from those of principal arterials. Therefore, assumptions made on the general effect of the predictor variables from typical safety performance functions may not apply to lower roadway classes. This research sought to explore those gaps in the roadway safety research domain. To accomplish this objective, roadway characteristics were collected along with traffic volume and crash data for greater than 13,000 miles of two-lane roadways in rural, urban, and suburban areas from across the state of Michigan for the period of 2011 through 2018. A series of safety performance functions were developed using a mixed-effects negative binomial modeling structure, which included fixed-effects and random-effects to account for the unobserved heterogeneity associated with varying design standards and site characteristics. The results indicated that driveway density significantly influences crash occurrence across all land-use categories for paved highways, although no impact was observed on unpaved roads. Commercial driveways possessed a stronger effect on crash occurrence than residential driveways or industrial driveways. In urban areas, posted speed limit had a significant positive association with crash frequency, and this effect increased when the speed limit exceeded 40 mph. The effect of speed limit was stronger on urban minor arterial segments (compared to collectors) and for fatal and injury crashes (compared to property damage only). This research also assessed the safety impacts associated with horizontal curve characteristics on rural highway segments, including curve type, curve direction, curve-approaching, curve-following, and inner-curve tangent distances, and curve design speed on rural two-lane undivided highways. Similar to prior research, curves with design speeds lower than the posted speed limit showed elevated crash occurrence. Most notably, compound and reverse curves were associated with greater crash occurrence compared to simple curves, with the greatest impact by the reverse curves. The increased approaching tangent distance for the simple curve or the first of a series of compound or reverse curves increased crash likelihood, perhaps due to the decreased driver expectancy for curvature with increasing tangent distance. However, increased inner-curve tangent distance was found to be associated with decreased crash occurrence. Lastly, the left-turning curves were found to be associated with greater crash occurrence than that on the right-turning curves.
Author: Meghna Chakraborty Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 206
Book Description
Evaluating the safety performance of roadway segments and intersections typically involves associating traffic crashes, injuries, and fatalities to various roadway and traffic characteristics, which typically vary broadly between rural and urban contexts. In rural areas, roadway geometric characteristics often play a critical role in the safety performance of a given roadway, while myriad other factors, including driveways and intersections, tend to have a greater influence on urban roadway safety. However, certain geometric aspects, such as the characteristics of the horizontal curvature and the impact of driveway land-use type have not been well-explored in prior roadway safety research. There has also been limited research on the safety performance for roadways of lower functional classifications, such as minor arterial and collector roadways, which comprise a substantial portion of the nationwide roadway network but are often designed to lower standards and possess driver and trip characteristics that typically differ from those of principal arterials. Therefore, assumptions made on the general effect of the predictor variables from typical safety performance functions may not apply to lower roadway classes. This research sought to explore those gaps in the roadway safety research domain. To accomplish this objective, roadway characteristics were collected along with traffic volume and crash data for greater than 13,000 miles of two-lane roadways in rural, urban, and suburban areas from across the state of Michigan for the period of 2011 through 2018. A series of safety performance functions were developed using a mixed-effects negative binomial modeling structure, which included fixed-effects and random-effects to account for the unobserved heterogeneity associated with varying design standards and site characteristics. The results indicated that driveway density significantly influences crash occurrence across all land-use categories for paved highways, although no impact was observed on unpaved roads. Commercial driveways possessed a stronger effect on crash occurrence than residential driveways or industrial driveways. In urban areas, posted speed limit had a significant positive association with crash frequency, and this effect increased when the speed limit exceeded 40 mph. The effect of speed limit was stronger on urban minor arterial segments (compared to collectors) and for fatal and injury crashes (compared to property damage only). This research also assessed the safety impacts associated with horizontal curve characteristics on rural highway segments, including curve type, curve direction, curve-approaching, curve-following, and inner-curve tangent distances, and curve design speed on rural two-lane undivided highways. Similar to prior research, curves with design speeds lower than the posted speed limit showed elevated crash occurrence. Most notably, compound and reverse curves were associated with greater crash occurrence compared to simple curves, with the greatest impact by the reverse curves. The increased approaching tangent distance for the simple curve or the first of a series of compound or reverse curves increased crash likelihood, perhaps due to the decreased driver expectancy for curvature with increasing tangent distance. However, increased inner-curve tangent distance was found to be associated with decreased crash occurrence. Lastly, the left-turning curves were found to be associated with greater crash occurrence than that on the right-turning curves.
Author: Steven York Stapleton Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 188
Book Description
Safety on rural highways continues to be a serious concern in the United States. While only 20 percent of the population live in rural areas, approximately one-half of motor vehicle fatalities occur on rural roadways, resulting in a rural fatal crash rate that is approximately double that of urban areas. In many states, most rural arterial highways are owned by the state department of transportation. However, several states, including Michigan, possess a large rural county highway network. For example, nearly 75 percent of the approximately 120,000 miles of public roadways in Michigan are owned by one of the 83 county road agencies across the state.County-owned highways typically possess characteristics that differ considerably from those owned by the state department of transportation, which limits the usefulness of safety performance functions (SPFs) and crash modification factors (CMFs) generated based on state highways, including those found in the Highway Safety Manual (HSM). Thus, assumptions made from models generated using data from state highways may not apply county highways due to differences in traffic, design, and maintenance. As a substantial proportion of rural crashes occur on county roads, identification of factors affecting safety performance on rural county roads is critical to support highway safety improvement programs and development of design standards.A cross-sectional safety performance analysis was performed for county highway segments and stop-controlled intersections throughout rural Michigan, including both federal aid and non-federal aid highways, as well as paved and unpaved road surfaces. SPFs were developed using mixed effects negative binomial regression to determine the safety effect of various design elements and site characteristics, including cross-sectional and geometric characteristics, which were included in the models as fixed effects. Random intercepts were incorporated into the models to account for unobserved heterogeneity between counties and between individual sites.One particularly noteworthy contribution of this research was to investigate the impacts of horizontal curvature on safety performance. Curve radii data extracted from the Michigan roadway shapefile allowed for the safety performance effects of decreasing curve design speed to be assessed in an incremental manner. Horizontal curves on paved county roads with design speeds below 40 mph experienced crash occurrence that was more than four times greater than segments without substandard curvature. On unpaved roadways, such curves experienced three times greater crash occurrence compared to segments without substandard curvature. Deer-related crashes, however, were shown to be fewer in frequency along horizontal curves.For stop-controlled intersections, skew angle was a variable of interest. At rural four-leg stop-controlled intersections, skew angles between 10 and 39 degrees were associated with increased crash frequency at intersections across all intersection classes. Skew had the greatest effect when the major road was county non-federal aid, where skew angles between 10 and 39 degrees experienced 60 percent more crashes than intersections without skew. Considering federal-aid intersections, the skew effect was diminished by approximately one-half.As expected, county-specific SPFs differed from models previously developed for state highways, including the SPFs included in the HSM. Generally speaking, at intersections, county highways were found to experience fewer crashes per unit of traffic volume than state highways, with county non-federal aid highways showing the lowest crash occurrence. County highway segments tend to have higher crash frequency than state roads. However, this is not the case at all traffic volumes, which further shows the need for county-specific safety performance models.
Author: Rameshwor Chalise Publisher: ISBN: 9781369182194 Category : Low-volume roads Languages : en Pages : 182
Book Description
The American Association of State Highway and Transportation Officials, AASHTO’s Highway Safety Manual (HSM) was first released in 2010 and is considered as a significant milestone in the advancement of the practice of road safety analysis. An extensive workforce spearheaded by the Transportation Research Board (TRB) Committee gave a result in the form of the first Highway Safety Manual in the United States. The HSM has already been proven as a great asset in traffic safety practice and also in research related to traffic safety since it bridges the gap between the state-of-the-art of research and practice. The HSM’s analytical tools and techniques help to quantify the traffic safety and help in evaluation as well as decision making in planning design, operation, and maintenance. There are a number of states and transportation authorities which are already using the HSM along with the AASHTO design guide. Although the HSM is the sole national source for quantitative evaluation of traffic safety, it has some limitations and there remains some room for improvement. Safety Performance Functions are statistical models to predict the expected number of crashes per year for a certain roadway facility as a function of traffic, and, in some cases, roadway characteristics, and weather conditions. Simple SPFs are mostly developed using Average Annual Daily Traffic (AADT) only while Full SPFs consider additional factors to traffic such as roadway geometry, driver characteristics, and weather conditions. Part C-Predictive Methods in the HSM includes the calibration procedure of SPFs as well as guidelines on how to calibrate jurisdiction-specific SPFs. The main limitation in the HSM Part C is that the Safety Performance Functions (SPFs) for different road facilities were developed using data from only few states in the United States. Thus the provided SPFs cannot adequately represent all states and regions since each of the states has a different geographical features, weather conditions, crash reporting thresholds, and demographic attributes. The main goal of this research is to apply and validate some of the HSM parts; Part C, to Wyoming specific conditions. In this thesis, Wyoming-specific SPFs were developed using crash data and traffic data from 2003 to 2013 for both total crashes and fatal and injury (F+I) crashes. All the rural two-lane two-way roadways and interstate freeways were considered in developing Wyoming-specific Simple SPFs, however, segments were chosen randomly from different parts of the state to develop Wyoming-specific Full SPFs. Negative Binomial (NB) model was used to develop SPFs for both interstate freeways and two-lane two-way roadways. Also, Zero-Inflated Poisson (ZIP) model was developed for two-lane two-way roadways and compared with the NB model. Statistical goodness-of-fit tests were performed on the calibrated models. The results were compared in order to assess the transferability of the HSM SPFs in Wyoming. It was found that the HSM SPFs cannot be applied directly in the state of Wyoming. While Simple SPFs under-estimated and over-estimated the number of crashes for different roadway segments and severity levels, Wyoming-specific Full SPFs provided more accurate and precise crash prediction.
Author: H. R. Pasindu Publisher: Springer Nature ISBN: 303087379X Category : Technology & Engineering Languages : en Pages : 917
Book Description
This volume gathers the latest advances, innovations, and applications in the field of pavement technology, presented at the 12th International Conference in Road and Airfield Pavement Technology (ICPT), hosted by the University of Moratuwa, Sri Lanka, and held on July 14-16, 2021. It covers topics such as pavement design, evaluation and construction, pavement materials characterization, sustainability in pavement engineering, pavement maintenance and rehabilitation techniques, pavement management systems and financing, transportation safety, law and enforcement related to pavement engineering, pavement drainage and erosion control, GIS applications, quarry material assessment, pavement instrumentation, IT and AI applications in pavement. Featuring peer-reviewed contributions by leading international researchers and engineers, the book is a timely and highly relevant resource for materials scientists and engineers interested in pavement engineering.
Author: Jonathan James Kay Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 0
Book Description
The use of alternative intersection designs can provide both safety and operational benefits for road users at potentially lower costs when implemented in the appropriate setting. The Federal Highway Administration has previously recognized a subset of alternative intersections designs broadly referred to as "reduced left-turn conflict intersections" as a proven safety countermeasure that have been shown to decrease the risk of potentially severe crash types by reducing conflict points through the use of indirect left-turn movements. Median U-turn intersections (also referred to as "Michigan lefts" or "boulevard turnarounds") are one such alterative design that accommodates indirect left-turn movements via directional U-turn crossovers located within the median along one or both of the intersecting roadways. Michigan has long been a pioneer in the implementation of median U-turns along urban and suburban divided boulevards, with initial installations dating back several decades. Additionally, various indirect left-turn configurations have been implemented along rural highways and frontage roads for urban freeways.While prior work has consistently demonstrated that median U-turn intersection designs represent an effective countermeasure that can improve operational performance and reduce the frequency of severe crash types when implemented in the appropriate context, much of the extant research is outdated and several important areas of investigation remain unexplored. This includes defining the appropriate crash influence area, the impacts of pre-conversion characteristics, impacts to pedestrian and bicycle collisions, and evaluating crashes pre/post conversion (e.g., longitudinal panel data) compared to a purely cross-sectional evaluation. To address these and other knowledge gaps, research was performed to quantify the safety performance characteristics and develop analytical tools related to the utilization of median U-turn intersections. Historical traffic crash data were collected for signalized and unsignalized intersections in Michigan where left-turns are accommodated by a median U-turn design. To allow for comparison of the performance between the median U-turn and traditional designs, data were also collected for a sample of reference intersections (divided and undivided) where conventional direct left-turn movements were maintained. A novel approach was developed to define the safety performance influence area of a median U-turn intersection, which subsequently improved the method of identifying and collecting target crash data. Utilizing the traffic crash data, a series of analyses were performed to identify the differences between conventional and median U-turn intersections, and to also identify the differences in safety performance between various median U-turn design characteristics. The analyses compared crash rates, types, severity distributions, and severe injury collision patterns, and included development of series of safety performance functions and crash modification factors. The results were then generalized into a series of recommendations for roadway agencies considering future implementation of median U-turn intersections, including specific design recommendations intended to improve safety performance for all road users.Ultimately, it was concluded that median U-turn designs represent an effective safety countermeasure to target the reduction of severe crash types for both unsignalized and signalized intersections. While there are some potential tradeoffs with respect to non-injury crash frequencies for specific pre-conversion configurations, the use of these indirect left-turn intersection designs is consistent with the Safe System approach adopted by the United States Department of Transportation within the National Roadway Safety Strategy. Unsignalized median U-turn intersections offer superior fatal and injury crash performance compared to conventional unsignalized intersections. The removal of the crossing conflict points at unsignalized median U-turn designs (which include a closed median at the intersection) essentially eliminates the pattern of severe head on left-turn and angle collisions occurring within conventional intersections. However, it is important to recognize that non-injury crashes were shown to increase when converting a conventional unsignalized intersection to a median U-turn at locations with an existing median on the major roadway.Signalized median U-turn intersections offer superior safety performance for both injury and non-injury crashes compared to conventional signalized intersections along undivided roadways. However, the comparison of median U-turns locations to conventional divided signalized intersections was limited by a lack of reference sites with comparable traffic volumes. Annual average frequencies of severe pedestrian and bicycle crashes were similar between the signalized median U-turn and conventional undivided sites. Finally, several design features of signalized median U-turn intersections were identified as having a significant impact on safety performance, including the distance to crossovers from the main intersection, the length of weaving areas, the number of signalized crossovers, and the number of storage lanes.
Author: Douglas W. Harwood Publisher: ISBN: Category : Low-volume roads Languages : en Pages : 204
Book Description
This report presents an algorithm for predicting the safety performance of a rural two-lane highway. The accident prediction algorithm consists of base models and accident modification factors for both roadway segments and at-grade intersections on rural two-lane highways. The base models provide an estimate of the safety performance of a roadway or intersection for a set of assumed nominal or base conditions. The accident modification factors adjust the base model predictions to account for the effects on safety for roadway segments of lane width, shoulder width, shoulder type, horizontal curves, grades, driveway density, two-way left-turn lanes, passing lanes, roadside design and the effects on safety for at-grade intersections of skew angle, traffic control, exclusive left- and right-turn lanes, sight distance, and driveways. The accident prediction algorithm is intended for application by highway agencies to estimate the safety performance of an existing or proposed roadway. The algorithm can be used to compare the anticipated safety performance of two or more geometric alternatives for a proposed highway improvement. The accident prediction algorithm includes a calibration procedure that can be used to adapt the predicted results to the safety conditions encountered by any particular highway agency on rural two-lane highways. The algorithm also includes an Empirical Bayes procedure that can be applied to utilize the safety predictions provided by the algorithm together with actual site-specific accident history data.
Author: Meghna Chakraborty
Author: Meghna Chakraborty
Author: Steven York Stapleton
Author: Steve Kuciemba
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Author: Rameshwor Chalise
Author: H. R. Pasindu
Author: Jonathan James Kay
Author: Douglas W. Harwood
Author: 
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