Systematic Safety Evaluation of Diverging Diamond Interchanges Based on Nationwide Implementation Data

2021 ◽  
pp. 036119812110049
Author(s):  
Ahmed Abdelrahman ◽  
Mohamed Abdel-Aty ◽  
Jinghui Yuan ◽  
Ma’en M. A. Al-Omari
Keyword(s):  
Empirical Bayes ◽  
Safety Evaluation ◽  
Safety Performance ◽  
Cross Sectional ◽  
Crash Frequency ◽  
Left Turn ◽  
Crash Modification Factors ◽  
Diamond Interchanges ◽  
Implementation Data ◽  
Sectional Analysis

Diverging diamond interchanges (DDIs) are designed as an alternative to the conventional diamond interchanges to enhance operational and safety performance. As the popularity of the DDI is increasing and more DDIs are being constructed and proposed, the need has arisen to measure the actual safety benefits of DDIs as compared with the traditional diamond interchanges. This study evaluates the safety of DDIs using three methods: before–after study with comparison group, Empirical Bayes before–after method, and cross-sectional analysis. This study collected a nationwide sample of 80 DDIs in 24 states. The estimated crash modification factors indicated that converting conventional diamond interchange to DDIs could significantly decrease the total, fatal-and-injury, rear-end, and angle/left-turn crashes by 14%, 44%, 11%, and 55%, respectively. Moreover, the developed safety performance functions implied that a longer distance between crossovers/ramp terminals and a lower speed limit on freeway exit ramps are significantly associated with lower crash frequency at diamond interchanges. This study contributes to the existing literature using a relatively large representative sample size, which provides more reliable evaluation results. In addition, this study also explored the effects of different traffic and geometric characteristics on the safety performance of DDIs.

Safety Evaluation of Median U-Turn Crossover-Based Intersections

2020 ◽  
Vol 2674 (7) ◽  
pp. 206-218
Author(s):  
Ma’en Mohammad Ali Al-Omari ◽  
Mohamed Abdel-Aty ◽  
Jaeyoung Lee ◽  
Lishengsa Yue ◽  
Ahmed Abdelrahman
Keyword(s):  
Opposite Direction ◽  
Safety Evaluation ◽  
Decision Makers ◽  
Property Damage ◽  
Cross Sectional ◽  
Left Turn ◽  
Single Vehicle ◽  
Crash Modification Factors ◽  
Traffic Operation ◽  
Crash Reduction

Alternative innovative designs for intersections were defined to enhance traffic operation and safety. Median U-turn (MUT) and restricted crossing U-turn (RCUT) intersections are among the types of alternative intersections that enable drivers to make left-turn movements at median U-turn crossovers downstream of the main intersection. Recently, municipalities and transport agencies have tended to implement these types of intersections. However, their effectiveness in crash reduction has not been adequately determined in previous studies. This is because of the limited number of alternative intersections that were considered in these studies. In addition, there was no consideration for the unusual new geometric design of these intersections. In this study, a safety evaluation was conducted while considering the new intersection-related areas at MUT and RCUT intersections to clarify and quantify their effectiveness in crash reduction. This study considered 73 MUT and 12 RCUT intersections. Two types of MUT intersections were considered in this study. Crash modification factors for MUT and RCUT intersections were estimated by using before–after and cross-sectional methods. The results indicated that MUT and RCUT intersections are safer than conventional intersections. MUT intersections are effective in reducing total, property damage only (PDO), rear-end, and opposite-direction sideswipe crashes, although they significantly increase single-vehicle and non-motorized crashes. RCUT intersections are effective in reducing fatal-and-injury, injury, head-on, and angle crashes. Findings of this research provide clear evaluation for decision makers about the effectiveness of MUT and RCUT intersections in crash reduction.

Safety Evaluation for Turnarounds at Diamond Interchanges: Assessing the Texas U-Turn

2018 ◽  
Vol 2672 (17) ◽  
pp. 61-71 ◽  
Author(s):  
Karen K. Dixon ◽  
Raul E. Avelar ◽  
Maryam Shirinzadeh Dastgiri ◽  
Bahar Dadashova
Keyword(s):  
Performance Assessment ◽  
Safety Evaluation ◽  
Safety Performance ◽  
Sampled Data ◽  
Data Set ◽  
Left Turn ◽  
Reliable Assessment ◽  
Street Traffic ◽  
Diamond Interchanges ◽  
Longitudinal Distance

Texas frontage road turnarounds at diamond interchange locations are a common treatment in the State of Texas. This configuration, also often referred to as the Texas U-turn, allows vehicles traveling on a one-way frontage road to access the opposing direction one-way frontage road via a U-turn before the terminal intersections at the diamond interchange. This technique removes two potential left-turn maneuvers from the adjacent at-grade intersections. The frontage road turnaround has operational benefits that result from shifting vehicles that would typically be occupying the intersection. The safety of these turnaround configurations, however, is not well known. This paper focuses on the observed safety performance of these turnaround configurations at diamond freeway interchanges in Texas. The authors first developed a large randomly sampled data set to facilitate a statistically reliable assessment of U-turn safety performance for Texas interchanges. Next they conducted a safety performance assessment at locations with and without turnarounds and determined that site features that significantly influence the number of crashes include the volume of cross street traffic, the cross street right-turn configuration at frontage roads, the minimum radius in the turnaround, the longitudinal distance from the U-turn exit to the closest downstream driveway, and the number of lanes on each frontage road. The safety performance findings at locations with and without turnarounds suggests that an agency could construct a turnaround to enhance facility operations with the knowledge that construction will not adversely impact safety. Although the research introduced in this paper focuses on Texas locations, the findings should be applicable to similar facilities in other states if the turnaround conditions are similar.

Evaluation of Protected Left-Turn Phasing and Leading Pedestrian Intervals Effects on Pedestrian Safety

2021 ◽  
pp. 036119812110255
Author(s):  
Elissa Goughnour ◽  
Daniel Carter ◽  
Craig Lyon ◽  
Bhagwant Persaud ◽  
Bo Lan ◽  
...  
Keyword(s):  
New York ◽  
Empirical Bayes ◽  
Pedestrian Safety ◽  
The United States ◽  
Public Health Issue ◽  
Crash Frequency ◽  
Left Turn ◽  
Crash Modification Factors ◽  
Pedestrian Crashes ◽  
Benefit Cost

Pedestrian safety is an important public health issue for the United States, with pedestrian fatalities representing approximately 16% of all traffic-related fatalities in 2016. Nationwide, transportation agencies are increasing their efforts to implement engineering-based improvements that increase pedestrian safety. These agencies need statistically rigorous crash modification factors (CMFs) to demonstrate the safety effectiveness of such countermeasures, and to apply in benefit–cost analyses to justify their implementation. This study focused on developing CMFs for two countermeasures that show promise for improving pedestrian safety: protected or protected/permissive left-turn phasing, and leading pedestrian intervals (LPIs). Data were acquired from four North American cities that had installed one or both of the countermeasures of interest: Chicago, IL; New York City, NY; Charlotte, NC; and Toronto, ON. The empirical Bayes before–after study design was applied to estimate the change in expected crash frequency for crashes following treatment. The protected left-turn phasing evaluation showed a benefit in reducing vehicle–vehicle injury crashes, but did not produce statistically significant results for vehicle–pedestrian crashes. For those crashes a disaggregate analysis did reveal that this treatment could be especially beneficial where pedestrian volumes exceed 5,500 per day. The LPI evaluation showed a statistically significant reduction in vehicle–pedestrian crashes with an estimated CMF of 0.87.

Safety Evaluation of Freight Intermodal Connectors in Tennessee State

2019 ◽  
Vol 2673 (3) ◽  
pp. 237-246
Author(s):  
Deo Chimba ◽  
Emmanuel Masindoki ◽  
Xiaoming Li ◽  
Casey Langford
Keyword(s):  
Traffic Safety ◽  
Statistical Significance ◽  
Safety Evaluation ◽  
Crash Frequency ◽  
Left Turn ◽  
Crash Rates ◽  
Signal Density ◽  
Geometric Factors ◽  
Last Mile ◽  
Average Annual Daily Traffic

This paper evaluates the traffic safety along freight intermodal connectors (FICs), which are also known as “first mile/last mile roadways,” connecting facilities that link freight-intensive land uses to main freight routes. Using Tennessee’s FICs as a case study, the paper digests the safety with reference to crash frequency, crash rates, and statistical significance of attributing traffic and geometric factors. It was found that connectors leading to pipeline terminals have high crash rates (almost double) compared with other type of terminals, whereas port terminal connectors have the lowest safety problem indices. The study established correlative contributing causes of crash frequencies and rates along FICs that included average annual daily traffic, lanes, shoulders, access, and median types. Traffic signal density was found to strongly and significantly affect the probability of crashes, together with the presence of a two-way left-turn lane (TWLTL), which surprisingly tends to decrease the probability of crashes along these connectors. The presence of shoulders along intermodal connectors was found to help reduce the probability of crashes, whereas the presence of curb and gutter tends to increase crash frequency. Analysis indicated that most of the FICs with high crash rates were also operating at a lower traffic operations level of service (LOS), especially for critical movements toward freight facilities because of high truck volumes.

Safety Performance Functions for Signalized Intersections in Large Urban Areas

2005 ◽  
Vol 1908 (1) ◽  
pp. 165-171 ◽  
Author(s):  
Craig Lyon ◽  
Anwar Haq ◽  
Bhagwant Persaud ◽  
Steven T. Kodama
Keyword(s):  
Urban Areas ◽  
Empirical Bayes ◽  
Signalized Intersections ◽  
Safety Performance ◽  
Signalized Intersection ◽  
Left Turn ◽  
Side Impacts ◽  
Recent Interest ◽  
Safety Performance Functions ◽  
Network Screening

This paper describes the development of safety performance functions (SPFs) for 1,950 urban signalized intersections on the basis of 5 years of collision data in Toronto, Ontario, Canada. Because Toronto has one of the largest known, readily accessible, urban signalized intersection databases, it was possible to develop reliable, widely applicable SPFs for different intersection classifications, collision severities, and impact types. Such a comprehensive set of SPFs is not available for urban signalized intersections from data for a single jurisdiction, despite the considerable recent interest in use of these functions for analyses related to network screening, and the development, prioritization, and evaluation of treatments. The application of a straightforward recalibration process requiring relatively little data means that the SPFs calibrated can be used by researchers and practitioners for other jurisdictions for which these functions do not exist and are unlikely to exist for some time. The value of the functions is illustrated in an application to evaluate a topical safety measure—left-turn priority treatment for which existing knowledge is on a shaky foundation. The results of this empirical Bayes evaluation show that this treatment is quite effective for reducing collisions, particularly those involving left-turn side impacts.

Safety Performance of Flashing Yellow Arrow for Protected–Permissive Left-Turn Signal Control in Central Illinois

2017 ◽  
Vol 2636 (1) ◽  
pp. 32-42 ◽  
Author(s):  
Kerrie L. Schattler ◽  
Eric P. Anderson ◽  
Trevor Hanson
Keyword(s):  
Empirical Bayes ◽  
Safety Evaluation ◽  
Left Turn ◽  
Turn Signal ◽  
Crash Data ◽  
Flashing Yellow Arrow ◽  
Before And After ◽  
Control Research ◽  
Central Illinois ◽  
Yellow Arrow

In 2010, the Illinois Department of Transportation began implementing the flashing yellow arrow (FYA) at intersections operating with protected–permissive left-turn (PPLT) control. Research was conducted to evaluate the safety-effectiveness of FYAs at 86 intersections and 164 approaches in central Illinois. The effectiveness evaluation was performed with 3 years of before-and-after FYA installation crash data and the empirical Bayes method. In the before condition, the left-turn signals operated with a circular green display indicating the permissive interval of PPLT control using a five-section signal head. In the after condition, the FYA replaced the circular green display for the permissive interval of PPLT with a four-section signal head. Supplemental traffic signs were mounted on the mast arm adjacent to the left-turn signal at over half of the FYA installations. The results of the comprehensive safety evaluation of the FYA for PPLT control are presented. Analyses were also performed to assess the effects of the FYA supplemental signs and the effects of the FYA overall on two subsets of at-fault drivers: older drivers (age 65+) and younger drivers (age 16 to 21). The resulting mean crash modification factors for the targeted crash types ranged from 0.589 to 0.714. The findings of this research support the continued use of FYAs for PPLT control to improve safety at signalized intersections in central Illinois.

scholarly journals Rural two-lane two-way three-leg and four-leg stop-controlled intersections: predicting road safety effects

2017 ◽  
Vol 12 (2) ◽  
pp. 117-126 ◽  
Author(s):  
Salvatore Antonio Biancardo ◽  
Francesca Russo ◽  
Daiva Žilionienė ◽  
Weibin Zhang
Keyword(s):  
Estimating Equation ◽  
Safety Performance ◽  
Crash Frequency ◽  
Performance Function ◽  
Left Turn ◽  
Explanatory Variables ◽  
Crash Data ◽  
Safety Performance Function ◽  
Lane Width ◽  
Residuals Analysis

The study focused on grade-level rural two-lane two-way three-leg and two-lane two-way four-leg stop-controlled intersections located in the flat area with a vertical grade of less than 5%. The goal is to calibrate one Safety Performance Function at these intersections by implementing a Generalized Estimating Equation with a binomial distribution and compare to the results with yearly expected crash frequencies by using models mainly refered to the scientific literature. The crash data involved 77 two-lane two-way intersections, of which 25 two-lane two-way three-leg intersections are without a left-turn lane (47 with left-turn lane), 5 two-lane two-way four-leg intersections without a left-turn lane (6 with a left-turn lane). No a right-turn lane is present on the major roads. Explanatory variables used in the Safety Performance Function are the presence or absence of a left-turn lane, mean lane width including approach lane and a left-turn lane width on the major road per travel direction, the number of legs, and the Total Annual Average Daily Traffic entering the intersection. The reliability of the Safety Performance Function was assessed using residuals analysis. A graphic outcome of the Safety Performance Function application has been plotted to easily assess a yearly expected crash frequency by varying the Average Annual Daily Traffic, the number of legs, and the presence or absence of a left-turn lane. The presence of a left-turn lane significantly reduces the yearly expected crash frequency values at intersections.

scholarly journals Advancing the methodology for predicting the safety effects of highway design and operational elements

2021 ◽  
Author(s):  
Taha Saleem
Keyword(s):  
Human Error ◽  
Empirical Bayes ◽  
Road Traffic ◽  
Cross Sectional ◽  
Highway Design ◽  
Road Traffic Crashes ◽  
Cross Sectional Analysis ◽  
The World ◽  
The Cross ◽  
Sectional Analysis

Road traffic crashes are one of the major causes of deaths and injuries around the world killing approximately 1.2 million people and injuring over 50 million every year. One of the primary goals of transportation agencies around the world is to reduce crashes as well as minimize the potential for human error and provide a forgiving road environment. Estimating the safety effects of highway design and operational elements is essential in achieving this goal. This research is divided into two components aimed at advancing the methodology for estimating these effects. The first component looks at evaluating the potential of cross-sectional analysis for developing crash modification factors/functions (CMFs/CMFunctions) used to represent the effects of safety treatments on crashes. First, the cross-sectional approach was used to investigate the safety effects of horizontal curvature on rural two-lane highways, which would be impossible to evaluate with before-after data. Second, this approach was further evaluated using databases of sites that were actually treated and similar, but untreated reference sites. The treatment databases for this part consisted of combination rumble strips (center line plus shoulder), wet reflective pavement markings and intersection conflict warning systems. The results from the cross-sectional analysis were then compared to recent studies where empirical Bayes before-after analysis was conducted with the same dataset used for the cross-sectional analysis. The results were promising in that the effects from the cross-sectional and before-after studies were reasonably comparable in each case. In addition, it was possible in some cases to relate the CMF to application circumstances by developing CMFunctions, providing results that could not be achieved in the before-after studies. The second component of this research involved development of roundabout crash predictions using conflicting volumes and delays, which could only be estimated from turning movement counts that are rarely collected at roundabouts. The object was to determine whether the considerable extra effort to collect these data would be worthwhile. The developed models were compared to the traditional models based on approach flows. The results suggest that collecting turning movement data, which is also required for capacity analysis, would be worthwhile for evaluating roundabout safety.

Crash Modification Factors for the Flashing Yellow Arrow Treatment at Signalized Intersections

2018 ◽  
Vol 2672 (30) ◽  
pp. 142-152 ◽  
Author(s):  
Raghavan Srinivasan ◽  
Bo Lan ◽  
Daniel Carter ◽  
Sarah Smith ◽  
Kari Signor
Keyword(s):  
North Carolina ◽  
Empirical Bayes ◽  
Evaluation Method ◽  
Signalized Intersections ◽  
Left Turn ◽  
Flashing Yellow Arrow ◽  
Crash Modification Factors ◽  
Treatment Category ◽  
Using Data ◽  
Yellow Arrow

This paper presents the results of an evaluation of the flashing yellow arrow (FYA) treatment using data from signalized intersections in Nevada, North Carolina, Oklahoma, and Oregon. The evaluation method was an empirical Bayes before–after analysis. The treatments were divided into seven categories depending on the phasing system in the before period (permissive, protected–permissive, or protected), phasing system in the after period (FYA permissive or FYA protected–permissive), the number of roads where the FYA was implemented (one road or both roads), and the number of legs at the intersections (three or four). The first five treatment 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: left turn crashes and left turn with opposing through crashes. The reduction ranged from 15% to 50%, depending on the treatment category. Intersections that had at least one protected left turn phase in the before period and had FYA protected–permissive left turn phase in the after period experienced an increase in left turn crashes and left turn with opposing through crashes, indicating that replacing a fully protected left turn with FYA will likely cause an increase in left turn crashes.

Sign in / Sign up

Export Citation Format

Share Document