How Roundabout Entry Design Parameters Influence Safety

2018 ◽  
Vol 2672 (34) ◽  
pp. 73-84 ◽  
Author(s):  
Jan Novák ◽  
Jiří Ambros ◽  
Jindřich Frič
Keyword(s):  
Czech Republic ◽  
Significant Influence ◽  
Design Guidelines ◽  
Safety Performance ◽  
Design Parameters ◽  
Crash Frequency ◽  
Study Objective ◽  
The Czech Republic ◽  
Safety Performance Functions ◽  
Safety Effect

Roundabouts are considered the safest intersection design; however, the safety effect may not be satisfactory at each specific roundabout. This is true especially in countries where roundabout design is a relatively new concept, such as in the Czech Republic. Specifically, most Czech roundabout crashes were found to occur on entries. This motivated the presented study to investigate how entry design parameters influence safety on Czech roundabouts and, if possible, use the findings to update current Czech roundabout design guidelines. To this end, the study comprised three analyses: crash-based safety performance functions, speed analysis, and finally safety performance functions which incorporated speed. All three analyses proved that entry design parameters have a statistically significant influence on safety, in terms of crash frequency, severity and speeds. Given the study objective, this fact should be considered in Czech roundabout design guidelines.

Front steering design guidelines formulation for e-scooters considering the influence of sitting and standing riders on self-stability and safety performance

2021 ◽  
pp. 095440702199217
Author(s):  
Milan Paudel ◽  
Fook Fah Yap
Keyword(s):  
Preventive Measures ◽  
Recent Trend ◽  
Dynamic Performance ◽  
Design Guidelines ◽  
Safety Performance ◽  
Design Parameters ◽  
Single Track ◽  
Standing Posture ◽  
Last Mile ◽  
Current Design

E-scooters are a recent trend and are viewed as a sustainable solution to ease the first and last mile problem in modern transportation. However, an alarming rate of accidents, injuries, and fatalities have caused a significant setback for e-scooters. Many preventive measures and legislation have been put on the e-scooters, but the number of accidents and injuries has not reduced considerably. In this paper, the current design approach of e-scooters has been analyzed, and the most common range of design parameters have been identified. Thereafter, validated mathematical models have been used to quantify the performance of e-scooters and relate them with the safety aspects. Both standing and seated riders on e-scooters have been considered, and their influence on the dynamic performance has been analyzed and compared with the standard 26-in wheel reference safety bicycle. With more than 80% of the accidents and injuries occurring from falling or colliding with obstacles, this paper tries to correlate the dynamics of uncontrolled single-track vehicles with the safety performance of e-scooters. The self-stability, handling, and braking effect have been considered as major performance matrices. The analysis has shown that the current e-scooter designs are not as stable as the reference safety bicycle. Moreover, these e-scooters have been found unstable within the most common range of legislated riding velocity. The results corroborate with the general perception that the current designs of e-scooters are less stable, easy to lose control, twitchy, or wobbly to ride. Furthermore, the standing posture of the rider on the e-scooter has been found dangerous while braking to avoid any disturbances such as potholes or obstacles. Finally, the front steering design guidelines have been proposed to help modify the current design of e-scooters to improve the dynamic performance, hence the safety of the e-scooter riders and the surroundings.

scholarly journals Crash Prediction Models for Horizontal Curve Segments on Two-Lane Rural Roads in Thailand

2021 ◽  
Vol 13 (16) ◽  
pp. 9011
Author(s):  
Nopadon Kronprasert ◽  
Katesirint Boontan ◽  
Patipat Kanha
Keyword(s):  
Prediction Models ◽  
Safety Performance ◽  
Horizontal Curve ◽  
Crash Frequency ◽  
Rural Roads ◽  
Crash Prediction ◽  
Road Crashes ◽  
Highway Safety Manual ◽  
Safety Performance Functions ◽  
Crash Prediction Models

The number of road crashes continues to rise significantly in Thailand. Curve segments on two-lane rural roads are among the most hazardous locations which lead to road crashes and tremendous economic losses; therefore, a detailed examination of its risk is required. This study aims to develop crash prediction models using Safety Performance Functions (SPFs) as a tool to identify the relationship among road alignment, road geometric and traffic conditions, and crash frequency for two-lane rural horizontal curve segments. Relevant data associated with 86,599 curve segments on two-lane rural road networks in Thailand were collected including road alignment data from a GPS vehicle tracking technology, road attribute data from rural road asset databases, and historical crash data from crash reports. Safety Performance Functions (SPFs) for horizontal curve segments were developed, using Poisson regression, negative binomial regression, and calibrated Highway Safety Manual models. The results showed that the most significant parameter affecting crash frequency is lane width, followed by curve length, traffic volume, curve radius, and types of curves (i.e., circular curves, compound curves, reverse curves, and broken-back curves). Comparing among crash prediction models developed, the calibrated Highway Safety Manual SPF outperforms the others in prediction accuracy.

scholarly journals The Development of Safety Performance Functions for Roundabouts in Amman, Jordan

2019 ◽  
Vol 296 ◽  
pp. 01006 ◽  
Author(s):  
Diana AL- Nabulsi ◽  
Khair Jadaan
Keyword(s):  
Urban Areas ◽  
Developed Countries ◽  
Safety Performance ◽  
Statistical Tool ◽  
Crash Frequency ◽  
Road Crashes ◽  
Design Variables ◽  
Safety Performance Functions ◽  
Strong Relation ◽  
Pedestrian Crossing

It is now well established that crash occurrences at roadway segments or intersections are associated with a large variety of factors. Safety Performance Functions (SPF) are statistical models developed to predict crash frequencies for various design variables. In Jordan, almost half of all road crashes occur at intersections, mostly in urban areas. There is a significant number of roundabouts throughout Amman which is increasing without evaluating their safety performance. To assess safety benefits of this kind of intersections, transportation professionals need the powerful statistical tool; the SPF. This study aims to develop SPFs for roundabouts in Amman. The models consider the crash frequency, traffic volume and geometric features of all the studied 20 roundabouts. The developed SPFs were statistically significant (R^2 = 0.91) .The findings of the study revealed that crash frequency has a strong relation with the AADT, roundabout entry angle-degrees, entry path radius, splitter radius, pedestrian crossing structure, inscribed diameter, central diameter, circulating width, entry width, number of circle legs. The developed SPFs are evaluated through a comparison with others from developed countries.

scholarly journals Development of Safety Performance Functions: Incorporating Unobserved Heterogeneity and Functional Form Analysis

2018 ◽  
Vol 2672 (30) ◽  
pp. 9-20 ◽  
Author(s):  
Behram Wali ◽  
Asad J. Khattak ◽  
Jim Waters ◽  
Deo Chimba ◽  
Xiaobing Li
Keyword(s):  
Unobserved Heterogeneity ◽  
Random Parameter ◽  
Safety Performance ◽  
Validation Dataset ◽  
Segment Length ◽  
Significant Heterogeneity ◽  
Crash Frequency ◽  
Form Analysis ◽  
Safety Performance Functions ◽  
Functional Forms

To improve transportation safety, this study applies Highway Safety Manual (HSM) procedures to roadways while accounting for unobserved heterogeneity and exploring alternative functional forms for Safety Performance Functions (SPFs). Specifically, several functional forms are considered in Poisson and Poisson-gamma modeling frameworks. Using 5 years (2011–2015) of crash, traffic, and road inventory data for two-way, two-lane roads in Tennessee, fixed- and random-parameter count data models are calibrated. The models account for important methodological concerns of unobserved heterogeneity and omitted variable bias. With a validation dataset, the calibrated and uncalibrated HSM SPFs and eight new Tennessee-specific SPFs are compared for prediction accuracy. The results show that the statewide calibration factor is 2.48, suggesting rural two-lane, two-way road segment crashes are at least 1.48 times greater than what HSM SPF predicts. Significant variation in four different regions in Tennessee is observed with calibration factors ranging between 2.02 and 2.77. Among all the SPFs considered, fully specified Tennessee-specific random parameter Poisson SPF outperformed all competing SPFs in predicting out-of-sample crashes on these road segments. The best-fit random parameter SPF specification for crash frequency includes the following variables: annual average daily traffic, segment length, shoulder width, lane width, speed limit, and the presence of passing lanes. Significant heterogeneity is observed in the effects of traffic exposure-related variables on crash frequency. The study shows how heterogeneity-based models can be specified and used by practitioners for obtaining accurate crash predictions.

scholarly journals Assessing Safety Performance on Urban and Suburban Roadways of Lower Functional Classification: A Comparison of Minor Arterial and Collector Roadway Segments

2021 ◽  
Author(s):  
Meghna Chakraborty ◽  
Timothy Gates
Keyword(s):  
Safety Performance ◽  
Speed Limit ◽  
General Effect ◽  
Crash Frequency ◽  
Mixed Effect ◽  
Fatal Injury ◽  
Crash Data ◽  
Random Intercept ◽  
Safety Performance Functions ◽  
Washtenaw County

Previous research of urban roadway safety performance has generally focused on roadways of high functional classifications, such as principal arterials. However,roadways with lower functional classifications, including minor arterials and collectors, typically possess characteristics that differ from those of higher roadway classes. Therefore, assumptions made on the general effect of the predictor variables from typical safety performance functions may not apply to lower roadway classes. Toaddress these knowledge gaps, a safety performance evaluation of urban/suburban minor arterial and collector roadway segments was performed using traffic androadway data along with eight years of crash data from 189 miles of two-lane urban and suburban roadways in Washtenaw County, Michigan. Mixed-effect negativebinomial models with segment-specific random intercept were developed for minor arterial and collector road segments, considering total, fatal+injury, and propertydamage only crashes. In general, minor arterial roadways showed greater crash occurrence compared to collector roads. Posted speed limit had a significant positiveassociation with crash frequency, and this effect increased when the speed limit exceeded 40 mph. The effect of speed limit was stronger on minor arterial segmentsand for fatal+injury crashes. Additionally, driveway density was found to have a significant effect on safety performance, which was stronger for commercial/industrialdriveways compared to residential driveways and for collector roads compared to minor arterials, particularly when considering residential driveways. On-street parkingwas associated with lower crash occurrence, with a stronger effect on collector roadways, likely due to greater parking turnover when compared to minor arterials.

scholarly journals The Use of Rubber Dam among Czech Dental Practitioners

2011 ◽  
Vol 54 (4) ◽  
pp. 144-148 ◽  
Author(s):  
Martin Kapitán ◽  
Zdeňka Šustová
Keyword(s):  
Czech Republic ◽  
Significant Influence ◽  
Endodontic Treatment ◽  
Undergraduate Training ◽  
The Czech Republic ◽  
Professional Career ◽  
Rubber Dam ◽  
Dental Practitioners ◽  
Direct Payments ◽  
Conferences And Congresses

Rubber dam is considered an ideal device for tooth isolation. Nevertheless, its usage is quite rare in the Czech Republic. The aim of this study was: firstly, to gather and evaluate information regarding the use of rubber dam by dentists in the Czech Republic and to compare it with other countries; secondly to find out whether there are any influencing factors as to rubber dam usage; and finally to find out frequency of rubber dam use separately in endodontic treatment and in placing fillings of different materials. A questionnaire-based survey was conducted. Dentists filled in the questionnaires during dental conventions, educational events, conferences and congresses. Rubber dam was routinely used by less than eight per cent of the respondents (n = 35); less than twenty-two per cent of the respondents (n = 97) used rubber dam occasionally, and more than seventy per cent of the respondents (n = 317) has never use it. The results showed that rubber dam is not used frequently in the Czech Republic. If rubber dam is used, then it is typically for endodontic treatment or composite fillings. There were several factors with a statistically significant influence on the usage of rubber dam, such as gender, length of professional career, percentage of direct payments, previous experience in using rubber dam, and undergraduate training in rubber dam use.

scholarly journals Estimation of Safety Performance Functions (SPF) at signalized intersections in Medellín Colombia

DYNA ◽  
2020 ◽  
Vol 87 (214) ◽  
pp. 215-220
Author(s):  
Víctor Gabriel Valencia-Alaix ◽  
Basilio Restrepo Betancur ◽  
Cristhian Lizarazo Jimenez ◽  
Raul Andres Pineda Mendez
Keyword(s):  
Traffic Safety ◽  
Negative Binomial ◽  
Signalized Intersections ◽  
Safety Performance ◽  
Design Criteria ◽  
Binomial Model ◽  
Crash Frequency ◽  
Traffic Conditions ◽  
Safety Performance Functions

One of the objectives of road infrastructure sustainability is to ensure that users are treated equally and their quality of life is improved by providing better mobility and traffic safety. When designing roads, it is important to evaluate different design criteria alternatives - in this case, we look at traffic safety principles. For this, we used the Safety Performance Functions (SPF) tool to obtain the expected crash frequency. The data used were Medellín’s crash records from 2012 to 2016, as well as the geometric features and traffic conditions at signalized intersections. A negative binomial model was fitted to estimate the SPF. Exposure, geometry, and traffic volume were found to be statistically significant in determining the expected crash frequency for collisions where there was property damage only (PDO) and fatal or injury (FI). It was found that accidents were less likely on T-junctions compared to four-leg junctions, one-way approaches were found to be safer whereas right turns were found to increase collisions causing FI. 

Disaggregate Safety Performance Models for Signalized Intersections on Ontario Provincial Roads

1998 ◽  
Vol 1635 (1) ◽  
pp. 113-120 ◽  
Author(s):  
Bhagwant Persaud ◽  
Thu Nguyen
Keyword(s):  
Bayesian Framework ◽  
Signalized Intersections ◽  
Safety Performance ◽  
Data Availability ◽  
Empirical Bayesian ◽  
Time Period ◽  
Safety Performance Functions ◽  
Accident Severity ◽  
Safety Effect ◽  
Disaggregate Models

The more advanced methods for identifying unsafe intersections and evaluating the safety effect of treatment are based on an Empirical Bayesian framework that requires the use of safety performance functions relating the expected safety of an intersection to characteristics such as traffic flow. Aggregate and disaggregate models were developed to estimate the safety performance of three-legged and four-legged signalized intersections on Ontario provincial roads. Models were disaggregated by time period, accident severity, and environment class. Two levels of models were calibrated for different levels of data availability and model requirements. For Level 1, the safety of an intersection was estimated as a function of the sum of all entering flows; separate estimates were obtained for rear-end, right angle, and turning movement accidents, the three most prominent impact types. In Level 2, specific patterns were defined by the movements of involved vehicles prior to collision, and accidents for the main patterns at four-legged intersections were estimated as a function of flows relevant to each pattern. Aside from the theoretical aspects, the models provide a basis for comparison with available models for other jurisdictions. There are some novel aspects in that, unlike most models available for roads outside municipalities, the ones presented here do allow for safety estimates to be disaggregated by time period, accident severity, impact type, and accident pattern. Moreover, the calibrated models can be used in an Empirical Bayesian framework to estimate the safety of an individual intersection. This is an important feature generally lacking in available models.

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