Controlling Crest Vertical Curvature Rates Based on Variable Grade Stopping Sight Distance Calculation

2015 ◽  
Vol 2521 (1) ◽  
pp. 31-44
Author(s):  
Stergios Mavromatis ◽  
Nikiforos Stamatiadis ◽  
Basil Psarianos ◽  
George Yannis
Keyword(s):  
Design Parameters ◽  
Control Element ◽  
Mass Model ◽  
Road Design ◽  
Sight Distance ◽  
Wide Range ◽  
Significant Difference ◽  
Road Geometry ◽  
Stopping Sight Distance ◽  
Braking Process

Stopping sight distance (SSD) is a key control element that directly affects the suggested values of crucial road design parameters. Although there is a significant difference in SSD values between upgrades and downgrades, many design policies ignore the grade effect during vehicle braking on variable grades. Such a case occurs during the determination of crest vertical curvature rates in which the relevant SSD values are extracted assuming leveled road geometry. This paper investigates a possible deficiency of such an approach with regard to cases in which the length of the vertical curve exceeds the control SSD values. SSD calculation on variable grades during the braking process was addressed through a recently developed process that related the point mass model and the laws of mechanics. For a wide range of design speed values, charts illustrating the required SSDs were drawn as a function of negative ending grade values related to the control crest vertical curve rates adopted by AASHTO. The process revealed numerous SSD shortage areas for which revised crest vertical curvature rates were provided to grant SSD adequacy throughout the vehicles' braking process. This paper also aimed to provide designers with ready-to-use vertical design tools associated with amended vertical curvature rates to AASHTO's road functional classification as a function of the crest vertical curve's exit grade value.

scholarly journals Cognitive Load Variability from Road Characteristics Should Influence a Safety Requirement for Vehicle Stopping Sight Distance

2019 ◽  
Vol 63 (1) ◽  
pp. 2129-2133
Author(s):  
Cody A. Pennetti ◽  
Kelsey Hollenback ◽  
Inki Kim ◽  
James H. Lambert
Keyword(s):  
Reaction Time ◽  
Weather Conditions ◽  
Design Standards ◽  
Road Design ◽  
Adverse Weather Conditions ◽  
Sight Distance ◽  
Adverse Weather ◽  
Road Geometry ◽  
Stopping Sight Distance ◽  
Road Characteristics

Current U.S. geometric road design standards are based on a prescribed value for a driver’s perception-reaction time (a constant value of 2.5 seconds), which represents the time necessary for a driver to safely stop the vehicle to avoid a crash (referred to as a stopping sight distance); however, these standards fail to consider how road complexity, driver risk perception, and visual stimuli can influence perception-reaction time. With over a million vehicle fatalities a year (WHO, n.d.), it is necessary to investigate methods of improving driver safety. The influence of road characteristics is considered with some road design policies, but not currently applied to stopping sight distance. This paper introduces theoretical considerations for increasing perception-reaction time (and thereby adjusting speed limits or road geometry) based on roadway complexity (volume of vehicles, road geometry, pedestrian crossings, frequency of adverse weather conditions, or other conditions).

scholarly journals The Influence of Visibility Conditions in Horizontal Road Curves on the Efficiency of Noise Protection Barriers

2013 ◽  
Vol 2 (2) ◽  
pp. 22-32
Author(s):  
Tamara Džambas ◽  
Saša Ahac ◽  
Vesna Dragčević
Keyword(s):  
Minimum Distance ◽  
Noise Source ◽  
Design Parameters ◽  
Noise Barriers ◽  
Road Design ◽  
Sight Distance ◽  
Noise Barrier ◽  
Design Software ◽  
Stopping Sight Distance ◽  
Static Noise

Abstract Ensuring sufficient visibility on planned roads by sight distance testing is an integral part of every project, but problems with visibility can emerge when noise barriers are erected on existing roads. Namely, in order to provide sufficient noise protection, high noise barriers are often placed at minimum distance from the carriageway edge, and additional visibility testing in most cases is not carried out. Research described in this paper consists of stopping sight distance tests conducted by means of specialized road design software MX Road, and noise barrier optimization conducted by means of specialized noise prediction software LimA using static noise calculation method RLS 90. The aim of this research is to establish whether the required stopping sight distance on road sections where minimum design parameters are applied can be achieved if the noise barrier is placed at minimum distance from the carriageway edge, and to establish whether the optimized dimensions of planned noise protection barrier will change if the barrier is placed on larger distance from the noise source, which is, in this case, the existing road.

scholarly journals SIGHT DISTANCE ANALYSES IN ROAD DESIGN PROCESS: SERBIAN PRACTICE

Transport ◽  
2016 ◽  
Vol 31 (2) ◽  
pp. 250-259 ◽  
Author(s):  
Dejan Gavran ◽  
Sanja Fric ◽  
Vladan Ilić ◽  
Filip Trpčevski
Keyword(s):  
Cross Sections ◽  
3D Models ◽  
Software Tools ◽  
Design Parameters ◽  
Operating Speed ◽  
The Road ◽  
Road Design ◽  
Sight Distance ◽  
Road Geometry ◽  
Design Speed

New Serbian policies on road design introduce the concept of operating speeds. Decades ago, national policies were based on the constant design speed concept. Among other design parameters, in relation to that constant design speed, minimum radii of horizontal and vertical road geometry were determined. Introduction of the operating speed concept provides for more realistic prediction of speed levels along the road. Unlike the constant design speed, operating speed levels vary along the road, reaching higher levels in curves with larger radii, on straight sections and on reverse curves and dropping down to the design speed level in horizontal curves with the minimum radius. Consequently, besides a constant Stopping Sight Distance (SSD), which is calculated from the constant design speed, the new term, Required Sight Distance (RSD) is introduced. RSD varies along the road, as it is calculated from the operating speed, which also varies along the road. Appropriate RSD analyses are crucial on road rehabilitation projects, since a simple resurfacing that enables higher speed levels, without providing increased RSD, may hamper the safety of a newly resurfaced road. Software tools for predicting operating speed levels and optical analyses of the road are also presented in this paper. Software tools for RSD analyses enable the import of lines of sight into the 3D model of the roadway and their export into the cross sections extracted from the model, thus facilitating the obstacle removal. Also demonstrated are tools for determining Available Sight Distance (ASD), which are based on triangulated 3D models of the roadway as well.

scholarly journals A New Model of Stopping Sight Distance of Curve Braking Based on Vehicle Dynamics

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Rong-xia Xia ◽  
De-hua Wu ◽  
Jie He ◽  
Ya Liu ◽  
Deng-feng Shi
Keyword(s):  
Calculation Model ◽  
Emergency Situations ◽  
Process Dynamics ◽  
Sight Distance ◽  
Straight Line ◽  
Braking Distance ◽  
Vehicle Test ◽  
Stopping Sight Distance ◽  
Braking Process ◽  
Experimental Values

Compared with straight-line braking, cornering brake has longer braking distance and poorer stability. Therefore, drivers are more prone to making mistakes. The braking process and the dynamics of vehicles in emergency situations on curves were analyzed. A biaxial four-wheel vehicle was simplified to a single model. Considering the braking process, dynamics, force distribution, and stability, a stopping sight distance of the curve braking calculation model was built. Then a driver-vehicle-road simulation platform was built using multibody dynamic software. The vehicle test of brake-in-turn was realized in this platform. The comparison of experimental and calculated values verified the reliability of the computational model. Eventually, the experimental values and calculated values were compared with the stopping sight distance recommended by the Highway Route Design Specification (JTGD20-2006); the current specification of stopping sight distance does not apply to cornering brake sight distance requirements. In this paper, the general values and limits of the curve stopping sight distance are presented.

Calibrating Design Guidelines using Mental Workload and Reliability Analysis

2020 ◽  
Vol 2674 (8) ◽  
pp. 360-369
Author(s):  
Karim Habib ◽  
Maged Gouda ◽  
Karim El-Basyouny
Keyword(s):  
Human Factors ◽  
Reliability Analysis ◽  
Mental Workload ◽  
Design Guidelines ◽  
Horizontal Curves ◽  
Road Design ◽  
Sight Distance ◽  
Stopping Sight Distance ◽  
The Many ◽  
Time Required

The generic nature of road design is indiscriminate to age, race, or gender, as it is implicitly assumed that there are few behavioral differences between drivers while traversing various alignment elements (e.g., horizontal curves, tangential segments, etc.). For instance, the perception reaction time required, which is based on an 85th percentile value, on a tangent section is the same as that on a horizontal curve. This suggests that current guidelines do not consider the complexity that some geometric features might induce on drivers, and consequently, there is a need to address the many considerations of diversity. In this respect, human factors should be explicitly included in design guidelines. One aspect of human factors that has received little attention in the literature is related to the mental workload. In this study, a procedure is presented to estimate the mental workload for stopping sight distance. Then, reliability analysis is conducted to compare the change in the probability of non-compliance owing to the available sight distance and based on the mental workload. By analyzing data from 12 horizontal curves in Alberta, Canada, the probability of non-compliance dropped from 9.1% to 0.7%, and a moderate correlation with collisions was found. The results of the analysis showed that incorporating mental workload into the geometric design process can improve safety performance.

Reliability indices for road geometric design

1992 ◽  
Vol 19 (5) ◽  
pp. 760-766 ◽  
Author(s):  
Francis P. D. Navin
Keyword(s):  
Reliability Index ◽  
Design Parameters ◽  
Limit States ◽  
Highway Design ◽  
Reliability Indices ◽  
The Road ◽  
Modifying Factors ◽  
Sight Distance ◽  
Margin Of Safety ◽  
Stopping Sight Distance

Highway engineers, when asked to state the safety of a particular design, are usually at a loss to give a single meaningful measure as is possible in structural or geotechnical engineering. This paper outlines a method to estimate the margin of safety and reliability index for isolated highway components. The stopping sight distance is used to demonstrate the method. The method uses the basic highway design equations. On the assumption that the variables are random, the expected value of the mean and the variance are estimated; and from these the margin of safety and the reliability index are calculated. The most likely combination of variables for the existing design condition may also be estimated. The variables included represent the characteristics of the driver, the vehicle, and the road surface.A method is proposed to specify the design parameter's value representing a road's strategic importance, the users, the vehicles, the drivers, the environment, the terrain, and the standard of design and construction. The apparent advantage of the proposed reliability-based method is that the designer must explicitly specify the importance of the modifying factors and may also more closely investigate the behaviour of the variables in the design parameters in the critical region near noncompliance. Key words: limit states design, stopping sight distance, safety, highway design, reliability.

Three-Dimensional, Probabilistic Highway Design

2008 ◽  
Vol 2060 (1) ◽  
pp. 10-18 ◽  
Author(s):  
Mohamed Sarhan ◽  
Yasser Hassan
Keyword(s):  
Reliability Analysis ◽  
Probabilistic Approach ◽  
Three Dimensional ◽  
Design Parameters ◽  
Horizontal Curve ◽  
Vertical Alignment ◽  
Highway Design ◽  
Side Slope ◽  
Sight Distance ◽  
Stopping Sight Distance

The potential usefulness of reliability analysis has recently been stressed in many engineering applications. Given the variability in the design parameters, a reliability-based probabilistic approach is well suited to replace the current deterministic highway design practice. However, progress in this regard is generally slow. In this study, the reliability analysis was used to estimate the probability of hazard (POH) that might result from insufficiency of sight distances. As an application, the available sight distance was checked against required stopping sight distance on an assumed road segment. Variation of the design parameters was addressed with Monte Carlo simulation using 100,000 sets of design parameters based on distributions available in the literature. A computer program was developed to use these sets of design parameters to calculate the profiles of available and required stopping sight distances in two- and three-dimensional projections as well as the profile of POH. The approach was applied to a horizontal curve overlapping with flat grade, crest curves, and sag curves in a cut section where the side slope would restrict the sightline. The analysis showed that the current deterministic approach yields very conservative estimates of available and required stopping sight distance, resulting in very low POH. The application example also showed the change of POH with the change of vertical alignment parameters.

scholarly journals Reliability of stopping and decision sight distance at roundabouts

2021 ◽  
Author(s):  
Jafar Faizi
Keyword(s):  
Probabilistic Method ◽  
Design Parameters ◽  
Second Moment ◽  
First Order ◽  
State Highway ◽  
Sight Distance ◽  
Design Variables ◽  
First Order Second Moment ◽  
Stopping Sight Distance ◽  
Lateral Clearance

The existing Stopping Sight Distance (SSD) and Decision Sight Distance (DSD) design methods for roundabouts are deterministic. This means that all of the design variables are predetermined, fixed values. This study presents a probabilistic method for the determination of SSD and DSD at roundabouts based on the equation recommended by the American Association of State Highway and Transportation Officials (AASHTO 2011). The reliability-based method considers all design parameters as random variables. Three types of SSD (SSD for approaches, SSD along the circulatory lane, and SSD for exiting vehicles to the pedestrian crosswalk) were considered in this study. DSD was considered for roundabout approaches. The First-Order Second-Moment and Advanced First-Order Second-Moment methods were used to model SSD and DSD. Once the required SSD and DSD were determined, the lateral clearance requirements at every point of the roundabout were calculated.

scholarly journals Effects of vegetation type and horizontal curve radius on the rate of tree pruning to provide line of sight on main access roads

2014 ◽  
Vol 60 (No. 5) ◽  
pp. 208-211
Author(s):  
M. Nasiri ◽  
M.R. Pourmajidian
Keyword(s):  
Vegetation Type ◽  
Line Of Sight ◽  
Horizontal Curve ◽  
Horizontal Curves ◽  
Sight Distance ◽  
Hardwood Trees ◽  
Significant Difference ◽  
Stopping Sight Distance ◽  
Curve Radius ◽  
Tree Pruning

The present investigation was carried out to assess the influence of vegetation type and horizontal curve radius on the rate of tree pruning to provide the line of sight on horizontal curves in Caspian forests of Iran. For this purpose, the DBH (diameter at breast height) of trees around the curves which must be pruned was measured. Also, the horizontal curves radius was divided into 4 classes and for each class 10 horizontal curves (for each species) were selected and the species which required pruning were measured. The rate of radial pruning was determined to provide a minimum stopping sight distance by means of laser rangefinder along the line of sight. We found an inverse relationship between DBH and the rate of pruning. To provide sight vision, the radial pruning rate decreased regularly with the increasing radius of horizontal curves for coniferous species, while it increased irregularly for broadleaves. There was a significant difference in pruning between different radii of horizontal curves (P < 0.05). According to results, pruning should be done for mixed hardwood trees with widespread crowns and no sharp horizontal curves should be designed at the top or bottom of hills.  

scholarly journals Reliability of stopping and decision sight distance at roundabouts

2021 ◽  
Author(s):  
Jafar Faizi
Keyword(s):  
Probabilistic Method ◽  
Design Parameters ◽  
Second Moment ◽  
First Order ◽  
State Highway ◽  
Sight Distance ◽  
Design Variables ◽  
First Order Second Moment ◽  
Stopping Sight Distance ◽  
Lateral Clearance

The existing Stopping Sight Distance (SSD) and Decision Sight Distance (DSD) design methods for roundabouts are deterministic. This means that all of the design variables are predetermined, fixed values. This study presents a probabilistic method for the determination of SSD and DSD at roundabouts based on the equation recommended by the American Association of State Highway and Transportation Officials (AASHTO 2011). The reliability-based method considers all design parameters as random variables. Three types of SSD (SSD for approaches, SSD along the circulatory lane, and SSD for exiting vehicles to the pedestrian crosswalk) were considered in this study. DSD was considered for roundabout approaches. The First-Order Second-Moment and Advanced First-Order Second-Moment methods were used to model SSD and DSD. Once the required SSD and DSD were determined, the lateral clearance requirements at every point of the roundabout were calculated.

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