Safety Performance Of Rural Intersections With Atypical Design Characteristics
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Safety Performance Of Rural Intersections With Atypical Design Characteristics
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Author : Anthony Ingle
language : en
Publisher:
Release Date : 2022
Safety Performance Of Rural Intersections With Atypical Design Characteristics written by Anthony Ingle and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with Electronic dissertations categories.
The results described in this dissertation represent a culmination of the efforts in the study of safety performance at rural intersections with atypical design characteristics. The specificity of this topic does not limit its relevance to intersection safety and the science of relating infrastructure traits to failure risks. Statistical modelling is used to predict average crash frequency. The model specification uses attributes such as the average annual daily traffic (AADT) on the major and minor road approaches, among other characteristics, to account for the exposure to crashes of various defined types and severities.The atypical intersection geometries studied herein consist of offset-T, curved corner, highly skewed, and multi-leg with five or more intersection legs. All of the intersections studied are minor road stop-controlled, along two-lane two-way rural highways. An effort is made to summarize the outcomes in practically applicable terminology such as Crash Modification Factors (CMFs) so that the conclusions of this study can lend toward a safer transportation future.The investigation into offset-T intersections utilizes a series of random intercept negative binomial models for crash occurrence that was generated based on 10 years of crash data from a sample of 299 offset-T intersections and 301 four-leg intersections with minor stop-control along rural two-lane highways in Michigan. The search for candidate intersections was exhaustive, considering that both major and minor road AADT was desired for each site. The modeling technique used a random effect for each site (location). Models were developed for total (non-animal) intersection crashes, as well as for single motor vehicle, angle, and rear-end crash types. The effects of offset distance and direction were analyzed and incorporated into the models. Compared to conventional four-leg intersections, offset-T intersections exhibited 35 percent more crashes regardless of the offset distance or direction. Considering crash types, single motor vehicle crashes occurred more frequently at offset-T intersections, and increased as the offset distance increased. Rear end crashes also occurred more frequency at offset-T intersections, with left offsets having more crash occurrence than right offsets. However, angle crashes are 40 to 69 percent lower at offset-T intersections due to the elimination of the direct crossing maneuver. The CMF for converting an existing offset-T into a conventional four-leg intersection is 0.74 within the studied ranges of offset direction and distance. This equivalates to a 26 percent reduction in total (non-animal) crash frequency. At curved corner intersections, a random intercept negative binomial models for crash occurrence used geographic region as a random effect. A total intersection crash (non-animal) model was generated based on 10 years of crash data from a sample of 227 three-leg sites and 65 four-leg sites among curved corner intersection geometry only. Reliance on the availability of minor road AADT so severely limited the sample population that an estimation of minor road AADT was made in order to proceed with modeling. A minor road AADT estimation model uses national functional classification as well as surface type, population density, and major road traffic volume to estimate the minor road traffic. A table of CMFs is presented for potentially converting an existing configuration into a combined/merged approach that is consistent with a traditional countermeasure from MDOT Geometric Design Guidelines. At curved corner intersections, installing a combined/merged intersection approach near the midpoint of the curve is a potential countermeasure that can be expected to reduce the average intersection crash frequency by 25 percent for three-leg configurations. A larger radius of curvature along the curved segment at these types of intersections is also very favorable for safety performance. Each 100-foot increase in the radius of a three-leg or four-leg curved corner intersection is estimated to reduce crash occurrence by 5 percent and 8 percent respectively.The safety influence of intersection skew angle on rural two-lane two-way facilities was evaluated by calibrating crash modification factors. Ten years of crash history among federal aid and non-federal aid highways was used to develop crash modification functions at three-leg and four-leg stop-controlled intersections. Skew angle was investigated as a parameter in the SPF models both as a continuous variable, with observed values ranging from 0 to 80 degrees, and categorized into ranges. A few transformations of the skew parameter were considered such as the flexible form model having skew interaction with AADT (annual average daily traffic), and a Hoerl curve. Both three-leg and four-leg intersections exhibited an initially increasing trend of crash rates followed by a decreasing trend as skew angle increased. A categorical model was found to best describe the skew relationship using discrete skew angle ranges. Among three-leg intersections, a skew angle between 17 to 27 degrees experienced 22 percent more crashes than perpendicular intersections. However, more highly skewed three-leg intersections exhibited a decreasing relationship to increasing skew angle. Among four-leg intersections, a skew angle between 17 to 27 degrees experienced 40 percent more crashes, while intersections with a skew angle greater than 45 degrees did not have significantly different crash occurrence than perpendicular intersections. The implications of assuming a monotonic increasing relationship to skew angle are challenged as a result of this study. Multi-leg intersections with more than four approach legs constitute a rare circumstance, yet these sites experience higher than average crash frequencies compared to conventional four-leg intersections. Single-vehicle as well as angle and rear-end crash types are most likely to occur at multi-leg intersections based on the history of crashes observed.The procedures described in this study are consistent with the Highway Safety Manual (HSM) and subsequent state of the art research for the procurement of safety performance models for any variety of circumstances. By utilizing an expansive data set and geospatial mapping techniques, the analysis is extended to previously unexplored site types. The extension of predictive safety analysis to atypical intersection types with unique geometric characteristics helps to fill a gap in the current field of practice with the hope of achieving an ultimate goal toward zero deaths in motor vehicle transportation.
Safety Effectiveness Of Highway Design Features
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Author : Steve Kuciemba
language : en
Publisher:
Release Date : 1992
Safety Effectiveness Of Highway Design Features written by Steve Kuciemba and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1992 with Roads categories.
Safety Effectiveness Of Highway Design Features Intersections
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Author :
language : en
Publisher:
Release Date : 1992
Safety Effectiveness Of Highway Design Features Intersections written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1992 with Bicycle trails categories.
Safety Effectiveness Of Highway Design Features
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Author :
language : en
Publisher:
Release Date : 1992
Safety Effectiveness Of Highway Design Features written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1992 with Bicycle trails categories.
Safety Effectiveness Of Highway Design Features Volume V Intersections
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Author : Stephen R. Kuciemba
language : en
Publisher:
Release Date : 1992
Safety Effectiveness Of Highway Design Features Volume V Intersections written by Stephen R. Kuciemba and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1992 with categories.
Rural Expressway Intersection Characteristics That Contribute To A Reduced Safety Performance
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Author : Garrett David Burchett
language : en
Publisher:
Release Date : 2005
Rural Expressway Intersection Characteristics That Contribute To A Reduced Safety Performance written by Garrett David Burchett and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with categories.
Expressways have been constructed in many states as a way to increase mobility without the expense of a full access-controlled or grade-separated facility. In most cases, it was assumed that these segments of highway would produce similar mobility and safety characteristics as other access-controlled facilities. However, recent research has found that there are problems with the safety performance of these systems. Although past research has been completed to examine the nature of crashes on these facilities, it is the purpose of this study to continue the research and analyze the common characteristics of the intersections. The intersections studied in this research were located throughout the state of Iowa. The objective of these analyses is to provide an identification of the major contributing factors that create problematic intersections in the state of Iowa. From previous research, it is evident that factors in addition to roadway volume contribute to the safety performance of an at-grade, two-way, stop-controlled expressway intersection. This research identifies common characteristics that may increase or decrease the safety performance of a rural expressway intersection. The methodology used in this research includes the examination of 644 intersections throughout the state of Iowa. Through the use of a statewide database and crash information from 1996 to 2000, we were able to identify the 100 best- and 100 worst-performing intersections based on crash severity rate. With the 200 intersections, a statistical analysis was completed to determine the effects intersection design and surrounding land use have on the intersection's safety performance. The safety performance of intersections located on vertical/horizontal curves, skewed intersections, and varying surrounding land use were studied to determine their effects on rural expressway intersections. Following the completion of the analysis of the 200 intersections, 30 intersections with highest crash severity index rates were selected for more thorough, site-specific analysis. As part of this analysis, we examined the impact of land use adjacent to the intersection and the impact of peaking in hourly traffic volumes. The research identifies attributes that impact crash severity both negatively and positively. Through the identification of these attributes, designers and planners can more adequately address safety concerns on rural expressway intersections.
Assessing Safety Performance Of Roadway Characteristics In Rural And Urban Contexts
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Author : Meghna Chakraborty
language : en
Publisher:
Release Date : 2022
Assessing Safety Performance Of Roadway Characteristics In Rural And Urban Contexts written by Meghna Chakraborty and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with Electronic dissertations categories.
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.
Safety Performance Of Median U Turn Intersections
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Author : Jonathan James Kay
language : en
Publisher:
Release Date : 2022
Safety Performance Of Median U Turn Intersections written by Jonathan James Kay and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with Electronic dissertations categories.
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.
Applying Safety And Operational Effects Of Highway Design Features To Two Lane Rural Highways
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Author :
language : en
Publisher:
Release Date : 2003
Applying Safety And Operational Effects Of Highway Design Features To Two Lane Rural Highways written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2003 with categories.
Rural two-lane highways constitute a majority of the mileage of public roads in the United States. Rural two-lane highways have 40% of the total travel but experience 60% of the highway fatalities. During the 1980's and 1990's, research was carried out in the United States to quantify the safety and operational effects of various key geometric design features including: lane and shoulder widths; roadside safety; horizontal and vertical alignment; sight distance; rural intersections. Aggregating this research has resulted in a compendium of the safety benefits of certain geometric design features for two-lane rural highways which links design standards and safety. This aggregated research information provides a basis for software analysis of proposed highway designs to assess their expected safety performance as well as the traditional capacity performance. Application of these benefits and effects achieves a numerical methodology for safety in a similar manner as is commonly carried out for capacity. This compendium of the safety and operational benefits of highway design features is being deployed in the United States to state highway departments in advance of the release of the software based analysis system. For the covering abstract of this conference see ITRD number E211395.
Correlation Of Design And Control Characteristics With Accidents At Rural Multi Lane Highway Intersections
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Author : Peter A. Van Maren
language : en
Publisher:
Release Date : 1980
Correlation Of Design And Control Characteristics With Accidents At Rural Multi Lane Highway Intersections written by Peter A. Van Maren and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1980 with Roads categories.