Reliability Approach to Intersection Sight Distance Design

2000 ◽  
Vol 1701 (1) ◽  
pp. 42-52 ◽  
Author(s):  
Said M. Easa
Keyword(s):  
Extreme Values ◽  
Random Variable ◽  
Sight Distance ◽  
Component Design ◽  
Design Variables ◽  
Reliability Method ◽  
Design Values ◽  
Speed Perception ◽  
Mean And Variance ◽  
Design Speed

The intersection sight distance (ISD) design presented by AASHTO is based on extreme values of the component design variables such as design speed, perception–reaction time (a high percentile), and friction coefficient (a low percentile). A reliability method is presented, based on AASHTO, that does not rely on extreme values but instead considers the moments (mean and variance) of the probability distribution of each random variable. The method also accounts for correlations among the component random variables. In Cases I and II of AASHTO, the variations of the sight distance along both legs of the intersection are considered for both design and evaluation. For evaluation (involving an exiting obstruction), these variations are combined into a single variable that determines whether the corresponding sight line is obstructed. In Case III, only the sight distance leg along the major road has variations. The proposed method is straightforward and involves simple, closed-form mathematics for calculating sight distance and associated reliability. Sensitivity of ISD to various design variables is examined. ISD reliability-based values for various cases are presented from data reported in the literature, and results are compared with current AASHTO design values.

scholarly journals Reliability Analysis of Sight Distance for Stopcontrol Intersections on Horizontal Alignments

2021 ◽  
Author(s):  
Altaf Hussain
Keyword(s):  
Extreme Values ◽  
Safety Margin ◽  
Random Variable ◽  
Probability Of Failure ◽  
Major Road ◽  
Road Design ◽  
Sight Distance ◽  
Minor Road ◽  
Reliability Method ◽  
Design Speed

Intersection sight distance (ISO) for stop-control intersections refers to the provision of adequate sight distance between a minor-road stopped vehicle and a major-road vehicle. The AASHTO policy for ISO for intersections on straight roadways Is based on the extreme values of the component design variables, such as major-road design speed and time gap, and assumes that these variables are deterministic. This research presents a reliability method that considers the moments (mean and variance) of the probability distribution of each random variable instead of the extreme values. This reliability method also accounts for the correlations among the component random variables. A performance function in terms of a safety margin is defined as the difference between the expected available and expected required ISO. Relationships for the mean and standard deviation of the safety margin are developed using First- Order Second-Moment analysis. Design graphs for the obstruction location are established for different radii of horizontal curves, design speed, and probability of failure. The reliability method is very useful as it provides the reliability associated with I8D design values. For evaluation purposes, the method can be used to determine the probability of failure of a particular intersection for an existing obstruction and current traffic conditions. The method can also be used to design the obstruction location for a given probability of failure. It was found that the deterministic method generally provides a higher probability of failure when the obstruction is closer to the minor road.

scholarly journals Reliability Analysis of Sight Distance for Stopcontrol Intersections on Horizontal Alignments

2021 ◽  
Author(s):  
Altaf Hussain
Keyword(s):  
Extreme Values ◽  
Safety Margin ◽  
Random Variable ◽  
Probability Of Failure ◽  
Major Road ◽  
Road Design ◽  
Sight Distance ◽  
Minor Road ◽  
Reliability Method ◽  
Design Speed

Intersection sight distance (ISO) for stop-control intersections refers to the provision of adequate sight distance between a minor-road stopped vehicle and a major-road vehicle. The AASHTO policy for ISO for intersections on straight roadways Is based on the extreme values of the component design variables, such as major-road design speed and time gap, and assumes that these variables are deterministic. This research presents a reliability method that considers the moments (mean and variance) of the probability distribution of each random variable instead of the extreme values. This reliability method also accounts for the correlations among the component random variables. A performance function in terms of a safety margin is defined as the difference between the expected available and expected required ISO. Relationships for the mean and standard deviation of the safety margin are developed using First- Order Second-Moment analysis. Design graphs for the obstruction location are established for different radii of horizontal curves, design speed, and probability of failure. The reliability method is very useful as it provides the reliability associated with I8D design values. For evaluation purposes, the method can be used to determine the probability of failure of a particular intersection for an existing obstruction and current traffic conditions. The method can also be used to design the obstruction location for a given probability of failure. It was found that the deterministic method generally provides a higher probability of failure when the obstruction is closer to the minor road.

scholarly journals Reliability Analysis of Intersection Sight Distance at Roundabouts

2020 ◽  
Vol 5 (8) ◽  
pp. 67 ◽  
Author(s):  
Said M. Easa ◽  
Yang Ma ◽  
Shixu Liu ◽  
Yanqun Yang ◽  
Shriniwas Arkatkar
Keyword(s):  
Sight Distance ◽  
Reliability Method ◽  
First Order Second Moment ◽  
Design Values ◽  
Mean And Variance ◽  
Coefficients Of Variations ◽  
The Mean ◽  
Lateral Clearance ◽  
Second Moment Method ◽  
Special Case

This paper presents a reliability-based method for the design of intersection sight distance (ISD) at traffic roundabouts using the linear and nonlinear deceleration profiles of the entry vehicles. The reliability method is based on the first-order second moment method which is simple and relatively accurate compared with advanced methods. The nonlinear deceleration profile includes a shape parameter that produces the linear profile as a special case. Deterministic and reliability-based formulas for the required ISD for an approaching vehicle are developed for the entry vehicle on the left and the vehicle on the circulating roadway. Then, the design values of the ISD legs, applicable to any type of roundabout, are presented for different probabilities of non-compliance (Pnc) and different coefficients of variations. For the special case of single-lane symmetrical roundabouts, which have a well-defined geometry, the lateral clearance needs are established. The sensitivity analysis shows that ISD is very sensitive to both the mean and variance of the critical headway. The results show that the deterministic method results in ISD values that correspond to a very small Pnc, indicating that the method is very conservative. The proposed method, which provides flexibility in selecting ISD for any given Pnc, should be of interest to highway designers and practitioners to promote roundabout safety.

A Safety Factor Method for Reliability-Based Component Design

2021 ◽  
pp. 1-34
Author(s):  
Jianhua Yin ◽  
Xiaoping Du
Keyword(s):  
Safety Factor ◽  
Design Method ◽  
Deterministic Component ◽  
Reliability Based Design ◽  
Component Design ◽  
Design Variables ◽  
Wide Range ◽  
Reliability Method ◽  
Reliability Methods ◽  
Input Variables

Abstract Reliability-based design (RBD) identifies design variables that maintain reliability at a required level. For many routine component design jobs, RBD may not be practical as it requires nonlinear optimization and specific reliability methods, especially for those design jobs which are performed manually or with a spreadsheet. This work develops a practical approach to reliability-based component design so that the reliability target can be achieved by conducting traditional component design repeatedly using a deterministic safety factor. The new component design is based on the First Order Reliability Method, which iteratively assigns the safety factor during the design process until the reliability requirement is satisfied. In addition to several iterations of deterministic component design, the other additional work is the calculation of the derivatives of the design margin with respect to the random input variables. The proposed method can be used for a wide range of component design applications. For example, if a deterministic component design is performed manually or with a spreadsheet, so is the reliability-based component design. Three examples are used to demonstrate the practicality of the new design method.

scholarly journals Reliability analysis of truck escape ramp design

2021 ◽  
Author(s):  
Kaitlyn Ann Greto
Keyword(s):  
Reliability Analysis ◽  
Safety Margin ◽  
Rolling Resistance ◽  
Second Moment ◽  
First Order ◽  
Stopping Distance ◽  
Design Variables ◽  
Reliability Method ◽  
First Order Second Moment ◽  
Design Speed

The truck escape ramp design presented by the Transportation Association of Canada is based on deterministic values of the design variables which include the required stopping distance, design speed, rolling resistance, and grade. Currently, a reliability analysis of the design of truck escape ramps does not exist. This report presents two methods used to analyze the reliability of truck escape ramp design; the first order second moment reliability method and the advanced first order second moment reliability method. These methods do not rely on deterministic values rather the mean and variance (moments) of each random variable’s probability distribution. Each reliability method was used to analyze truck escape ramps with one grade and two grades, for a total of four cases. The results of each case are provided and discussed along with an application to two existing truck escape ramps. The results show that the advanced first order second moment reliability method ensures more accurate results as well as a larger safety margin in comparison to the first order second moment method due to the nature of the methodology itself which considers design points.

scholarly journals Analysis of passing sight distance using first-order reliability method

2021 ◽  
Author(s):  
Said Easa
Keyword(s):  
Safety Margin ◽  
Field Studies ◽  
Vehicle Speed ◽  
Second Moment ◽  
First Order ◽  
State Highway ◽  
Sight Distance ◽  
Design Variables ◽  
Reliability Method ◽  
First Order Second Moment

Current passing sight distance requirements for two lane highways by the American Association of State Highway and Transportation Officials are based on field studies conducted between 1938 and 1941 which use deterministic values for its design variables such as passing sight distance, speed of the passing vehicle, speed differential between the passed and passing vehicle etc. This report presents three methods to analyze reliability and serves as an extension to the revised model presented by Yasser Hassan, Said Easa and A.O.Abd El Halim whose model sought to improve older models by equally considering both observed passing behaviours of drivers and passing maneuvers that are consistent with two lane highways. Analysis of passing sight distance using first order second moment reliability method, advanced first order second moment and the ellipsoid approach to measure the probability of failure of the passing sight distance design, rely solely on the mean and variance (moments) of each randomly distributed variable in contrast to methods that rely only on deterministic values. Results show the advanced first order second moment and the ellipsoid approach provided more accurate results than first order second moment method which in turn provide a greater safety margin with the later also proving to be a much more robust and efficient method of performing a reliability

A Practical Safety Factor Method for Reliability-Based Component Design

2020 ◽  
Author(s):  
Jianhua Yin ◽  
Xiaoping Du
Keyword(s):  
Safety Factor ◽  
Design Method ◽  
Deterministic Component ◽  
Reliability Based Design ◽  
Component Design ◽  
Design Variables ◽  
Wide Range ◽  
Reliability Method ◽  
Reliability Methods ◽  
Input Variables

Abstract Reliability-based design (RBD) identifies design variables that maintain reliability at a required level. For many routine component design jobs, RBD may not be practical as it requires nonlinear optimization and specific reliability methods, especially for those design jobs which are performed manually or with a spreadsheet. This work develops a practical approach to reliability-based component design so that the reliability target can be achieved by conducting traditional component design repeatedly using a deterministic safety factor. The new component design is based on the First Order Reliability Method, which iteratively assigns the safety factor during the design process until the reliability requirement is satisfied. In addition to a number of iterations of deterministic component design, the other additional work is the calculation of the derivatives of the design margin with respect to the random input variables. The proposed method can be used for a wide range of component design applications. For example, if a deterministic component design is performed manually or with a spreadsheet, so it the reliability-based component design. Three examples are used to demonstrate the practicality of the new design method.

scholarly journals Analysis of passing sight distance using first-order reliability method

2021 ◽  
Author(s):  
Said Easa
Keyword(s):  
Safety Margin ◽  
Field Studies ◽  
Vehicle Speed ◽  
Second Moment ◽  
First Order ◽  
State Highway ◽  
Sight Distance ◽  
Design Variables ◽  
Reliability Method ◽  
First Order Second Moment

Current passing sight distance requirements for two lane highways by the American Association of State Highway and Transportation Officials are based on field studies conducted between 1938 and 1941 which use deterministic values for its design variables such as passing sight distance, speed of the passing vehicle, speed differential between the passed and passing vehicle etc. This report presents three methods to analyze reliability and serves as an extension to the revised model presented by Yasser Hassan, Said Easa and A.O.Abd El Halim whose model sought to improve older models by equally considering both observed passing behaviours of drivers and passing maneuvers that are consistent with two lane highways. Analysis of passing sight distance using first order second moment reliability method, advanced first order second moment and the ellipsoid approach to measure the probability of failure of the passing sight distance design, rely solely on the mean and variance (moments) of each randomly distributed variable in contrast to methods that rely only on deterministic values. Results show the advanced first order second moment and the ellipsoid approach provided more accurate results than first order second moment method which in turn provide a greater safety margin with the later also proving to be a much more robust and efficient method of performing a reliability

scholarly journals Reliability analysis of truck escape ramp design

2021 ◽  
Author(s):  
Kaitlyn Ann Greto
Keyword(s):  
Reliability Analysis ◽  
Safety Margin ◽  
Rolling Resistance ◽  
Second Moment ◽  
First Order ◽  
Stopping Distance ◽  
Design Variables ◽  
Reliability Method ◽  
First Order Second Moment ◽  
Design Speed

The truck escape ramp design presented by the Transportation Association of Canada is based on deterministic values of the design variables which include the required stopping distance, design speed, rolling resistance, and grade. Currently, a reliability analysis of the design of truck escape ramps does not exist. This report presents two methods used to analyze the reliability of truck escape ramp design; the first order second moment reliability method and the advanced first order second moment reliability method. These methods do not rely on deterministic values rather the mean and variance (moments) of each random variable’s probability distribution. Each reliability method was used to analyze truck escape ramps with one grade and two grades, for a total of four cases. The results of each case are provided and discussed along with an application to two existing truck escape ramps. The results show that the advanced first order second moment reliability method ensures more accurate results as well as a larger safety margin in comparison to the first order second moment method due to the nature of the methodology itself which considers design points.

Barrier Function Method in Reliability Based Design Optimization

2005 ◽  
Vol 297-300 ◽  
pp. 1882-1887
Author(s):  
Tae Hee Lee ◽  
Jung Hun Yoo
Keyword(s):  
Design Optimization ◽  
Barrier Function ◽  
Reliability Index ◽  
Feasible Solution ◽  
Reliability Based Design Optimization ◽  
User Requirement ◽  
Mean Values ◽  
Reliability Based Design ◽  
Design Variables ◽  
Reliability Method

In practical design applications, most design variables such as thickness, diameter and material properties are not deterministic but stochastic numbers that can be represented by their mean values with variances because of various uncertainties. When the uncertainties related with design variables and manufacturing process are considered in engineering design, the specified reliability of the design can be achieved by using the so-called reliability based design optimization. Reliability based design optimization takes into account the uncertainties in the design in order to meet the user requirement of the specified reliability while seeking optimal solution. Reliability based design optimization of a real system becomes now an emerging technique to achieve reliability, robustness and safety of the design. It is, however, well known that reliability based design optimization can often have so multiple local optima that it cannot converge into the specified reliability. To overcome this difficulty, barrier function approach in reliability based design optimization is proposed in this research and feasible solution with specified reliability index is always provided if a feasible solution is available. To illustrate the proposed formulation, reliability based design optimization of a bracket design is performed. Advanced mean value method and first order reliability method are employed for reliability analysis and their optimization results are compared with reliability index approach based on the accuracy and efficiency.

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