Highway Alignment: Three-Dimensional Problem and Three-Dimensional Solution

1998 ◽  
Vol 1612 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Yasser Hassan ◽  
Said M. Easa ◽  
A. O. Abd El Halim
Keyword(s):  
Three Dimensional ◽  
Computer Software ◽  
Geometric Design ◽  
Analytical Models ◽  
Dimensional Solution ◽  
Distance Analysis ◽  
Sight Distance ◽  
The Status ◽  
Current Design ◽  
Highway Alignment

Highway geometric design has usually been considered in separate two-dimensional (2-D) projections of horizontal and vertical alignments. Such a practice was followed mainly because three-dimensional (3-D) analysis of combined highway alignments was expected to be difficult. As a result, the effect of ignoring the 3-D nature of the highway alignment could not be quantified. With the long-term objective of developing 3-D design practice, a framework for 3-D highway geometric design was developed and 3-D sight distance was extensively studied as the first design basis. The status of sight distance in current design policies and previous research is summarized, and mainly 2-D analysis was considered. The five main tasks performed to cover the 3-D highway sight distance are presented. ( a) As a preliminary step, the 2-D sight distance on complex separate horizontal and vertical alignments was modeled, and the finite element method was used for the first time in the highway geometric design. ( b) The 2-D models were then expanded to cover the daytime and nighttime sight distances on 3-D combined alignments. ( c) The analytical models were coded into computer software that can determine the available sight distance on actual highway segments. ( d) The models were applied in 3-D design of combined horizontal and vertical curves in cut-and-fill sections, and preliminary design aids were derived. ( e) Finally, a new concept of red zones was suggested to mark the locations on alignments designed according to current practices where the available sight distance will drop below that required. A comprehensive work on 3-D sight distance analysis has been compiled that should be of great importance for highway researchers and professionals.

State-of-the-art of three-dimensional highway geometric design

1998 ◽  
Vol 25 (3) ◽  
pp. 500-511 ◽  
Author(s):  
Yasser Hassan ◽  
Said M Easa ◽  
A O Abd El Halim
Keyword(s):  
Traffic Safety ◽  
Vehicle Dynamics ◽  
Research Work ◽  
Three Dimensional ◽  
Computer Software ◽  
Design Criterion ◽  
Geometric Design ◽  
Analytical Models ◽  
Sight Distance ◽  
Current Standards

Geometric design is an important phase in the highway design process that is directly related to traffic safety. Highway elements should be jointly designed to account for such design criteria as sight distance, vehicle stability, driver comfort, drainage, and aesthetics. Intuitively, such a design should be based on a three-dimensional (3-D) analysis. This paper reviews the current practice and research work related to each design criterion with emphasis on the conformity with the 3-D nature of the highway. Current standards are based mainly on a two-dimensional (2-D) analysis that does not guarantee a satisfactory design. Recently, several research efforts have been expended in the 3-D highway analysis with sight distance being the most researched area. Analytical models and computer software have been developed to accurately model 3-D daytime and nighttime sight distances. Roads designed using current 2-D standards may compromise safety or economy. Different models are currently available to simulate the forces acting on a vehicle in 3-D. These models show that the point-mass formula for modelling vehicle dynamics in the current standards can be inaccurate. Current standards contain recommendations for drainage of surface water, but explicit quantitative coordination of combined alignments is lacking. Furthermore, research is still needed to study the effect of alignment coordination on highway aesthetics and driver's perception of information.Key words: highway geometric design, three-dimensional analysis, sight distance, vehicle dynamics, drainage, highway aesthetics.

Modeling Headlight Sight Distance on Three-Dimensional Highway Alignments

1997 ◽  
Vol 1579 (1) ◽  
pp. 79-88 ◽  
Author(s):  
Yasser Hassan ◽  
Said M. Easa ◽  
A. O. Abd El Halim
Keyword(s):  
Analytical Model ◽  
Three Dimensional ◽  
Computer Software ◽  
Major Elements ◽  
Geometric Design ◽  
Analytical Models ◽  
Horizontal Curve ◽  
Design Standards ◽  
Sight Distance ◽  
Element Technique

Sight distance is one of the major elements that must be considered in the geometric design to achieve safe and comfortable highways. Daytime sight distance has been extensively studied, and analytical models for two-dimensional (2-D) and three-dimensional (3-D) alignments have been developed. However, nighttime (headlight) sight distance has received less attention. Despite the higher accident rate during nighttime than during daytime, existing analytical models evaluating headlight sight distance are very primitive. Moreover, the interaction between the horizontal and vertical alignments has not been modeled. A four-phase analytical model for headlight sight distance on 3-D combined alignments is presented. The model is an application of the finite-element technique in highway geometric design. The model can determine the maximum distance that can be covered by the vehicle’s headlights and that is not obstructed by any sight obstructions including the road surface. On the basis of this analytical model, computer software was developed and used in a preliminary application for 3-D headlight sight distances on a sag or crest vertical curve combined with a horizontal curve. The application showed that the 3-D sight distance on sag vertical curves was generally lower than the corresponding 2-D value when the sag curve was overlapping with a horizontal curve. On the other hand, the overlapping of horizontal curves with crest vertical curves enhanced the 3-D sight distance. The difference between 2-D and 3-D sight distance values in both cases increased with a decrease in the horizontal curve radius and an increase in the pavement cross slope. The model was proved to be extremely valuable in establishing 3-D highway geometric design standards.

Sight distance red zones on combined horizontal and sag vertical curves

1998 ◽  
Vol 25 (4) ◽  
pp. 621-630 ◽  
Author(s):  
Yasser Hassan ◽  
Said M Easa
Keyword(s):  
Quantitative Analysis ◽  
Three Dimensional ◽  
The Other ◽  
Two Dimensional ◽  
Horizontal Curve ◽  
Sight Distance ◽  
Stopping Sight Distance ◽  
Three Dimensional Models ◽  
Highway Alignment ◽  
Current Standards

Coordination of highway horizontal and vertical alignments is based on subjective guidelines in current standards. This paper presents a quantitative analysis of coordinating horizontal and sag vertical curves that are designed using two-dimensional standards. The locations where a horizontal curve should not be positioned relative to a sag vertical curve (called red zones) are identified. In the red zone, the available sight distance (computed using three-dimensional models) is less than the required sight distance. Two types of red zones, based on stopping sight distance (SSD) and preview sight distance (PVSD), are examined. The SSD red zone corresponds to the locations where an overlap between a horizontal curve and a sag vertical curve should be avoided because the three-dimensional sight distance will be less than the required SSD. The PVSD red zone corresponds to the locations where a horizontal curve should not start because drivers will not be able to perceive it and safely react to it. The SSD red zones exist for practical highway alignment parameters, and therefore designers should check the alignments for potential SSD red zones. The range of SSD red zones was found to depend on the different alignment parameters, especially the superelevation rate. On the other hand, the results showed that the PVSD red zones exist only for large values of the required PVSD, and therefore this type of red zones is not critical. This paper should be of particular interest to the highway designers and professionals concerned with highway safety.Key words: sight distance, red zone, combined alignment.

Improved Design of Vertical Curves with Sight Distance Profiles

2003 ◽  
Vol 1851 (1) ◽  
pp. 13-24 ◽  
Author(s):  
Yasser Hassan
Keyword(s):  
Design Procedure ◽  
The United States ◽  
Analytical Models ◽  
Minimum Length ◽  
Vertical Alignment ◽  
The Road ◽  
Sight Distance ◽  
Special Cases ◽  
Current Design ◽  
Improved Design

Design of vertical alignment is one of the main tasks in highway geometric design. This task requires, among other things, that the designer ensure drivers always have a clear view of the road so they can stop before hitting an unexpected object in the road. Therefore, the ability to determine the required and available stopping sight distance (SSD) at any point of the vertical alignment is essential for the design process. Current design guides in the United States and Canada provide simple analytical models for determining the minimum length of a vertical curve that would satisfy the sight distance requirement. However, these models ignore the effect of grade on the required SSD. Alternative approaches and models have also been suggested but cover only special cases of vertical curves. Two specific models were expanded to determine the required SSD on crest and sag vertical curves. By comparing profiles of available SSD and required SSD on examples of vertical curves, it was shown that current North American design practices might yield segments of the vertical curve where the driver’s view is constrained to a distance shorter than the required SSD. An alternative design procedure based on the models was developed and used to determine the minimum lengths of crest and sag vertical curves. Depending on the approach grade, these new values of minimum curve length might be greater than or less than values obtained through conventional design procedures. Design aids were therefore provided in tabular form for designers’ easy and quick use.

scholarly journals Truck stability on different types of horizontal curves combined with vertical alignments

2021 ◽  
Author(s):  
Essam Mohamed S. A. E. A. Dabbour
Keyword(s):  
Three Dimensional ◽  
Computer Software ◽  
Design Guidelines ◽  
Vehicle Stability ◽  
Horizontal Curves ◽  
Different Types ◽  
Current Design ◽  
Single Compound ◽  
Margin Of Safety ◽  
Design Speed

The combination of horizontal curves with vertical alignments is commonly used in different classifications of highways; either on highway mainstream or on highway interchange ramps. The horizontal curves, combined with vertical alignments, may be single, compound or reverse horizontal curves. The current design guidelines do not adequately investigate vehicle stability on such three-dimensional (3D) alignments. Computer software that simulates vehicle behaviour on different geometrical alignments was employed to investigate vehicle stability on such 3D alignments. It was found that vehicle safety is questionable, especially for larger vehicles on reverse curves associated with vertical alignments. The critical speed, where the vehicle starts to rollover or skid, was found to be close to design speed for those 3D alignments. Design aids were then developed to address the recommended solutions to maintain the margin of safety required.

Analytical Model for Sight Distance Analysis on Three-Dimensional Highway Alignments

1996 ◽  
Vol 1523 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Yasser Hassan ◽  
Said M. Easa ◽  
A. O. Abd El Halim
Keyword(s):  
Three Dimensional ◽  
The Finite Element Method ◽  
Horizontal Curve ◽  
Design Standards ◽  
New Model ◽  
Distance Analysis ◽  
Horizontal Curves ◽  
Sight Distance ◽  
Proposed Model ◽  
Standards And Guidelines

Existing sight distance models are applicable only to two-dimensional (2-D) separate horizontal and vertical alignments or simple elements of these separate alignments (vertical curve, horizontal curve). A new model is presented for determining the available sight distance on 3-D combined horizontal and vertical alignments. The model is based on the curved parametric elements that have been used in the finite element method. The elements presented are rectangular (4-node, 6-node, and 8-node elements) and triangular. These elements are used to represent various features of the highway surface and sight obstructions, including tangents (grades), horizontal curves, vertical curves, traveled lanes, shoulders, side slopes, cross slopes, superelevation, lateral obstructions, and overpasses. The available sight distance is found analytically by examining the intersection between the sight line and the elements representing the highway surface and the sight obstructions. Application of the new model is illustrated using numerical examples, and the results show that existing 2-D models may underestimate or overestimate the available sight distance. The proposed model should be valuable in establishing design standards and guidelines for 3-D highway alignments and determining the effect of various highway features on sight distance.

Effect of driver and road characteristics on required preview sight distance

2002 ◽  
Vol 29 (2) ◽  
pp. 276-288 ◽  
Author(s):  
Yasser Hassan ◽  
Tarek Sayed
Keyword(s):  
Computer Animation ◽  
Linear Regression Analysis ◽  
Three Dimensional ◽  
Human Perception ◽  
Physical Modelling ◽  
Geometric Design ◽  
Geometric Parameters ◽  
Horizontal Curve ◽  
Sight Distance ◽  
Road Characteristics

Highway geometric design is a complex process that is closely related to human perception and behaviour. Among the human perception issues that can affect highway geometric design is the preview sight distance, which has been defined as the distance required to perceive a horizontal curve and react properly to it. Previous attempts to quantify preview sight distance included measurement on actual roads, physical modelling, and computer animation. This paper presents a computer animation experiment that was designed to examine the effects of geometric parameters and driver characteristics on preview sight distance and to statistically model preview sight distance. Statistical analysis showed that preview sight distance depends on geometric parameters such as the horizontal curve radius, use of spiral curve and its length, presence of crest vertical curve, algebraic difference of vertical grades, vertical curvature, and road delineation. On the other hand, driver characteristics were mostly found to be insignificant parameters. Finally, statistical models were developed to predict the value of preview sight distance using linear regression analysis. The models vary in simplicity and accuracy and were formulated as a function of the general alignment configuration or as a function of the exact geometric parameters.Key words: highway geometric design, sight distance, driver characteristics, three-dimensional alignment.

scholarly journals Truck stability on different types of horizontal curves combined with vertical alignments

2021 ◽  
Author(s):  
Essam Mohamed S. A. E. A. Dabbour
Keyword(s):  
Three Dimensional ◽  
Computer Software ◽  
Design Guidelines ◽  
Vehicle Stability ◽  
Horizontal Curves ◽  
Different Types ◽  
Current Design ◽  
Single Compound ◽  
Margin Of Safety ◽  
Design Speed

The combination of horizontal curves with vertical alignments is commonly used in different classifications of highways; either on highway mainstream or on highway interchange ramps. The horizontal curves, combined with vertical alignments, may be single, compound or reverse horizontal curves. The current design guidelines do not adequately investigate vehicle stability on such three-dimensional (3D) alignments. Computer software that simulates vehicle behaviour on different geometrical alignments was employed to investigate vehicle stability on such 3D alignments. It was found that vehicle safety is questionable, especially for larger vehicles on reverse curves associated with vertical alignments. The critical speed, where the vehicle starts to rollover or skid, was found to be close to design speed for those 3D alignments. Design aids were then developed to address the recommended solutions to maintain the margin of safety required.

Intersection Diagnostic Review Module: Expert System for Geometric Design Review of Intersections on Rural Two-Lane Highways

2003 ◽  
Vol 1851 (1) ◽  
pp. 3-12 ◽  
Author(s):  
Carrie Kindler ◽  
Richard M. Wood ◽  
Douglas W. Harwood ◽  
Timothy R. Neuman ◽  
Ingrid B. Potts ◽  
...  
Keyword(s):  
Expert System ◽  
Decision Rules ◽  
Geometric Design ◽  
Threshold Values ◽  
Design Decisions ◽  
Design Review ◽  
Sight Distance ◽  
Potential Safety ◽  
Literature Synthesis ◽  
Current Design

FHWA has sponsored the development of an expert system for diagnostic review of at-grade intersections on rural two-lane highways as a component of the Interactive Highway Safety Design Model (IHSDM). This system, the Intersection Diagnostic Review Module (IDRM), has been developed because conventional design practices and design review procedures often fail to explicitly address the safety consequences of geometric design decisions. In particular, combinations of geometric features may pose safety problems that current design policies do not address (e.g., an intersection in combination with a sharp horizontal curve and a steep grade). The expert system allows such problems to be identified and evaluated in an automated and organized fashion. The structure and knowledge base of this expert system are presented. The system identifies potential safety problems in an intersection design by applying decision rules based on models that quantify the extent to which particular problems may or may not be present. Established geometric design models (such as the sight distance models used in current design policies) as well as new models that have been developed from literature synthesis and judgments by geometric design and safety experts are included. The models that IDRM uses to identify potential safety problems and the threshold values used to determine whether particular problems exist are described. IDRM provides a series of advisory messages indicating design features that should be reviewed for potential safety-related concerns. The advisory messages are based on the nature and extent of concerns identified by comparison with established threshold values.

Validation of a Belt Model for Prediction of Hub Forces from a Rolling Tire4

2009 ◽  
Vol 37 (2) ◽  
pp. 62-102 ◽  
Author(s):  
C. Lecomte ◽  
W. R. Graham ◽  
D. J. O’Boy
Keyword(s):  
Internal Pressure ◽  
Equations Of Motion ◽  
Three Dimensional ◽  
Prediction Method ◽  
Analytical Models ◽  
Beam Model ◽  
Impedance Boundary ◽  
Bending Waves ◽  
Tire Rotation ◽  
Three Dimensional Models

Abstract An integrated model is under development which will be able to predict the interior noise due to the vibrations of a rolling tire structurally transmitted to the hub of a vehicle. Here, the tire belt model used as part of this prediction method is first briefly presented and discussed, and it is then compared to other models available in the literature. This component will be linked to the tread blocks through normal and tangential forces and to the sidewalls through impedance boundary conditions. The tire belt is modeled as an orthotropic cylindrical ring of negligible thickness with rotational effects, internal pressure, and prestresses included. The associated equations of motion are derived by a variational approach and are investigated for both unforced and forced motions. The model supports extensional and bending waves, which are believed to be the important features to correctly predict the hub forces in the midfrequency (50–500 Hz) range of interest. The predicted waves and forced responses of a benchmark structure are compared to the predictions of several alternative analytical models: two three dimensional models that can support multiple isotropic layers, one of these models include curvature and the other one is flat; a one-dimensional beam model which does not consider axial variations; and several shell models. Finally, the effects of internal pressure, prestress, curvature, and tire rotation on free waves are discussed.

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