This document discusses the alignment of highways, including horizontal and vertical elements. It covers topics such as grade line, horizontal and vertical curves, sight distance requirements, and super elevation. The key points are:
- Highway alignment consists of horizontal and vertical elements, including tangents and curves. Curves can be simple, compound, spiral, or reverse.
- Grade line refers to the longitudinal slope/rise of the highway. Factors in selecting a grade line include earthwork, terrain, sight distance, flood levels, and groundwater.
- Horizontal alignment deals with tangents and circular curves that connect changes in direction. Vertical alignment includes highway grades and parabolic curves.
- Proper design of curves
Here are the key steps and calculations for the homework:
1. Use design speed of 55 mph, emax of 4%, and fmax of 0.12 from Green Book
2. Calculate minimum radius using formula: Rmin = V2/(15(e+f)) = 1,200 ft
3. Select radius of 1,400 ft
4. Given: PI station of 352+44.97, Δ of 35° 24' 55"
5. Calculate curve length using L = ΔR/5729.58 = 1,260 ft
6. Calculate tangent length using T = Rtan(Δ/2) = 630 ft
7. Calculate PC station: PC = PI - T
This document provides information on geometric design concepts for highways, with a focus on vertical alignment and vertical curves. It includes definitions of terms like gradient, ruling gradient, limiting gradient, minimum gradient, and critical length of grade. It describes factors that influence grades like vehicle speed, acceleration and comfort. It also covers vertical curve fundamentals, including equations for crest and sag vertical curves based on stopping sight distance and headlight sight distance. Examples are provided for calculating sight distances and lengths for different grade change scenarios.
Geometric Design - Horizontal and vertical curvessachin dass
The document discusses key aspects of highway geometric design including horizontal and vertical alignment. It covers topics such as superelevation design, centrifugal force effects, transition curves, extra widening for curves, and vertical curve types. The key points are:
- Superelevation is used to counteract centrifugal force when negotiating curves, and its design considers factors like design speed, radius of curve, and coefficient of friction.
- Transition curves are used between tangents and circular curves to gradually change curvature and introduce superelevation for driver comfort.
- Extra widening is required for curves to accommodate off-tracking of vehicles and driver tendencies, calculated based on number of lanes, wheel base, design
The document discusses highway geometric design and its key elements. It aims to maximize safety, comfort and efficiency while minimizing costs and environmental impacts. Geometric design considers the road's alignment, cross-section, sight distances and intersections. Elements include the carriageway, shoulders, formation width, right of way, side slopes, berms and side drains. Camber and super elevation help drain water and counteract centrifugal forces on curves. Sight distance requirements like stopping sight distance ensure drivers can see far enough to stop safely.
The document discusses various aspects of vertical alignment in transportation infrastructure design and construction. It covers key components like gradient and ruling, the effects of gradient on vehicle resistance, and the design of vertical curves including summit and valley curves. Design parameters discussed include sight distance, centrifugal force, and length determination based on these factors. Equations are provided for calculating curve length and heights. The document also includes examples of previous questions asked on these topics in civil engineering examinations.
Often changes in the direction are necessitated in highway alignment due to various reasons such as topographic considerations, obligatory points.
The geometric design elements pertaining to horizontal alignment of highway should consider safe and comfortable movement of vehicles at the given design speed of the highway.
It is therefore necessary to avoid sudden changes in direction with sharp curves or reverse curves which could not be safely and conveniently negotiated by the vehicles at design speed.
Improper design of horizontal alignment of roads would necessitate speed changes resulting m higher accident rate and increase in vehicle operation cost.
Transition curve and Super-elevation
Transition Curve
Objectives of Transition Curve
Properties Of Transition Curve
Types Of Transition Curve
Length Of Transition Curve
Superelevation
Objective of providing superelevation
Advantages of providing superelevation
Superelevation Formula
Numerical
This document discusses various aspects of vertical alignment in transportation engineering. It describes how vertical alignment specifies the elevation of points along a roadway based on safety, comfort, drainage needs. Vertical curves are used to transition between different roadway grades and can be crest or sag curves. The coordination of vertical and horizontal alignment is also discussed to ensure driver safety and aesthetics. Maximum and minimum grades, as well as critical lengths of grades, are addressed based on truck performance.
Here are the key steps and calculations for the homework:
1. Use design speed of 55 mph, emax of 4%, and fmax of 0.12 from Green Book
2. Calculate minimum radius using formula: Rmin = V2/(15(e+f)) = 1,200 ft
3. Select radius of 1,400 ft
4. Given: PI station of 352+44.97, Δ of 35° 24' 55"
5. Calculate curve length using L = ΔR/5729.58 = 1,260 ft
6. Calculate tangent length using T = Rtan(Δ/2) = 630 ft
7. Calculate PC station: PC = PI - T
This document provides information on geometric design concepts for highways, with a focus on vertical alignment and vertical curves. It includes definitions of terms like gradient, ruling gradient, limiting gradient, minimum gradient, and critical length of grade. It describes factors that influence grades like vehicle speed, acceleration and comfort. It also covers vertical curve fundamentals, including equations for crest and sag vertical curves based on stopping sight distance and headlight sight distance. Examples are provided for calculating sight distances and lengths for different grade change scenarios.
Geometric Design - Horizontal and vertical curvessachin dass
The document discusses key aspects of highway geometric design including horizontal and vertical alignment. It covers topics such as superelevation design, centrifugal force effects, transition curves, extra widening for curves, and vertical curve types. The key points are:
- Superelevation is used to counteract centrifugal force when negotiating curves, and its design considers factors like design speed, radius of curve, and coefficient of friction.
- Transition curves are used between tangents and circular curves to gradually change curvature and introduce superelevation for driver comfort.
- Extra widening is required for curves to accommodate off-tracking of vehicles and driver tendencies, calculated based on number of lanes, wheel base, design
The document discusses highway geometric design and its key elements. It aims to maximize safety, comfort and efficiency while minimizing costs and environmental impacts. Geometric design considers the road's alignment, cross-section, sight distances and intersections. Elements include the carriageway, shoulders, formation width, right of way, side slopes, berms and side drains. Camber and super elevation help drain water and counteract centrifugal forces on curves. Sight distance requirements like stopping sight distance ensure drivers can see far enough to stop safely.
The document discusses various aspects of vertical alignment in transportation infrastructure design and construction. It covers key components like gradient and ruling, the effects of gradient on vehicle resistance, and the design of vertical curves including summit and valley curves. Design parameters discussed include sight distance, centrifugal force, and length determination based on these factors. Equations are provided for calculating curve length and heights. The document also includes examples of previous questions asked on these topics in civil engineering examinations.
Often changes in the direction are necessitated in highway alignment due to various reasons such as topographic considerations, obligatory points.
The geometric design elements pertaining to horizontal alignment of highway should consider safe and comfortable movement of vehicles at the given design speed of the highway.
It is therefore necessary to avoid sudden changes in direction with sharp curves or reverse curves which could not be safely and conveniently negotiated by the vehicles at design speed.
Improper design of horizontal alignment of roads would necessitate speed changes resulting m higher accident rate and increase in vehicle operation cost.
Transition curve and Super-elevation
Transition Curve
Objectives of Transition Curve
Properties Of Transition Curve
Types Of Transition Curve
Length Of Transition Curve
Superelevation
Objective of providing superelevation
Advantages of providing superelevation
Superelevation Formula
Numerical
This document discusses various aspects of vertical alignment in transportation engineering. It describes how vertical alignment specifies the elevation of points along a roadway based on safety, comfort, drainage needs. Vertical curves are used to transition between different roadway grades and can be crest or sag curves. The coordination of vertical and horizontal alignment is also discussed to ensure driver safety and aesthetics. Maximum and minimum grades, as well as critical lengths of grades, are addressed based on truck performance.
Signalized Intersections (Transportation Engineering)Hossam Shafiq I
This document provides an overview of signalized intersection analysis and optimization for a transportation engineering course. It defines key terms related to signal timing, describes methods for calculating vehicle delay under uniform and random traffic arrivals, and approaches for optimizing cycle length, green time allocation, and level of service. Examples are provided to illustrate calculations for critical lane group volume-to-capacity ratio, total lost time, optimal signal timing, green time distribution, and intersection level of service.
The document discusses the reasons for and methods of calculating the widening of pavements on horizontal curves. There are two types of widening: mechanical widening to account for vehicle off-tracking due to rigid wheel bases, and psychological widening to allow for greater driver maneuverability at higher speeds. Mechanical widening is calculated based on number of lanes, vehicle wheel base length, and curve radius. Psychological widening is also based on design speed and curve radius. The total widening is the sum of mechanical and psychological widening. Tables from the Indian Road Congress provide extra width recommendations for single and double lane pavements on curves.
Alignment: The position or the layout of the central line of the highway on the ground is called the alignment.
Highway Alignment includes both
a) Horizontal alignment includes straight and curved paths, the deviations and horizontal curves.
b) Vertical alignment includes changes in level, gradients and vertical curves.
This course provides an introduction to transportation engineering through five modules: transportation systems engineering, transportation planning, geometric design, pavement design, and traffic engineering. The objectives are to present a systems approach to transportation and describe the basic characteristics and models used in transportation planning, geometric design of highways, pavement design, and traffic engineering parameters and controls. The course aims to give students an overview of the interactions within transportation systems and the engineering concepts used in their planning, design, and operation.
This document discusses the key considerations for geometric design of highways. It covers standards for rural and urban roads, including lane widths, shoulders, sidewalks and bike lanes. It also discusses elements of horizontal and vertical alignment like curvature, sight distances, super elevation, transitions curves and gradients. Special considerations for designing highways through hilly terrain include ensuring stable slopes, adequate drainage, meeting geometric standards and minimizing unnecessary rises and falls in the road.
Geometric design of tracks aims to provide smooth and safe running of trains at maximum speed while carrying heavy loads. This involves proper design of gradients, curvature, and super elevation (cant).
There are different types of gradients - ruling gradient which is the maximum gradient permitted, momentum gradient which is steeper and uses train momentum, and pusher gradient requiring extra locomotives. Gradients are designed considering train performance and load. Curvature introduces greater resistance requiring grade compensation of ruling gradients.
Super elevation (cant) involves raising the outer rail on curves to counteract centrifugal forces. Equilibrium cant provides equal wheel load distribution. Higher speeds result in cant deficiency which must be limited for passenger safety. Contrary flexures like
Freeway & Highway LOS (Transportation Engineering)Hossam Shafiq I
This document discusses methods for determining freeway and highway level of service (LOS). It defines key terms like free-flow speed, passenger car equivalents, and LOS criteria. The document outlines how to calculate the free-flow speed by measuring it or using a baseline adjusted for factors like lane width. It also explains how to determine the traffic flow rate and convert volumes to passenger cars per lane per hour. Finally, it shows how to use the speed-flow curve and density to establish the LOS for a basic freeway segment based on traffic conditions.
This presentation deals with all the major steps involved in the survey, selection of the most possible route and the designing of the highway.
It will brief u on all the major topics of highway designing
This document discusses vertical alignment in road design. It defines vertical alignment as the vertical aspect of the road profile, including crest and sag curves. It describes the basic components of vertical alignment as grade and vertical curves. Grade is the slope of the road expressed as a percentage, while vertical curves are parabolic curves that provide gradual transitions between different grades to allow comfortable driving. The document discusses types of vertical curves such as sag curves at the bottom of hills and crest curves at the tops of hills, as well as symmetrical and unsymmetrical curves. It provides the equations used to design different types of vertical curves.
Mass-haul diagrams (MHDs) are used to calculate cut and fill volumes and estimate material hauling needs for construction projects. MHDs graphically display cumulative cut and fill volumes along the project centerline. They are used to determine balancing points where cut and fill volumes offset, how much material needs to be imported or exported, and the most economical hauling methods. An example MHD analysis identifies a project's maximum haul distance and calculates how much borrow material is needed to make up the excess fill volume.
Highway geometric design deals with dimensions and layout of visible features like horizontal and vertical alignments, sight distances, and intersections. Elements of geometric design include cross section, sight distance considerations, horizontal and vertical alignments, and intersections. Cross section elements comprise pavement characteristics, carriageway width, cross slope, median/separator, kerbs, road margins, and formation width. Horizontal alignment design considers factors like design speed, horizontal curves, super elevation, transition curves, pavement widening on curves, and setback distance. Super elevation is provided to counteract centrifugal forces on curves and is limited to a maximum of 7% as per Indian standards.
This document provides information on the geometric design of highways. It discusses the key elements of highway design including the width of the carriageway and roadway, right of way, shoulders, side slopes, medians, and design speed. The objectives of geometric design are to optimize efficiency, safety, and cost while minimizing environmental impacts. Standard widths and specifications for elements like carriageways, medians, and shoulders are provided based on highway class and roadway conditions.
A highway pavement is a structure consisting of superimposed layers of processed materials above the natural soil sub-grade, whose primary function is to distribute the applied vehicle loads to the sub-grade. The pavement structure should be able to provide a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics, and low noise pollution.
This document discusses railway turnouts. It begins by defining a turnout as the combination of points and crossings that allows a train to move from one track to another, either parallel or diverging. It then describes the key components of a turnout, including tongue rails, stock rails, lead rails, and a vee crossing. It also explains the classification of turnouts as left-hand or right-hand depending on the direction of diversion. Diagrams are included to illustrate the components and working principle of a turnout. The document concludes by stating that turnouts are essential for diverting traffic but can cause issues if not designed and maintained properly.
Vertical alignment of highway (transportation engineering)Civil Zone
Vertical curves are used in highway design to gradually transition between two different slopes or grades. There are two main types - crest vertical curves, which are used on roadway tops, and sag vertical curves, which are used on dips. The minimum length of a vertical curve is determined based on providing the required stopping sight distance for a given design speed. Additional criteria like passenger comfort, drainage, and appearance may also influence the curve length selected. Longer vertical curves generally provide a smoother ride but require more construction costs.
Railway Engineering-Curves and superelevationMani Vel
This document discusses curves and superelevation on railways. It defines horizontal and vertical curves, and explains that superelevation involves raising the outer rail on a curve to provide a comfortable ride. Superelevation counters the effects of lateral forces when negotiating a curve. The key points are:
- Superelevation is the difference in height between the inner and outer rails and helps distribute load on both rails.
- Equilibrium speed is when the centrifugal force is balanced by the cant (superelevation), providing no unbalanced radial acceleration.
- Maximum permissible speed considers factors like radius, cant, cant deficiency/excess, and transition length.
- Examples are provided to calculate supere
The document discusses the geometric design of roads, specifically horizontal curves. It covers key elements of geometric design like alignment, profile, and cross-section. Horizontal curve design is an important part that influences safety and efficiency. Parameters like design speed, superelevation, extra widening, and minimum radius are discussed in detail according to Indian Road Congress standards. Methods for building superelevation and effecting widening on curves are also summarized.
Determining equivalent single wheel load.(ESWL) Imran Nawaz
This document discusses methods for determining equivalent single wheel loads (ESWL) and equivalent single axle loads (ESAL) for pavement design. ESWL is defined as the load from a single tire that causes the same stresses/strains as a multi-wheel load. Methods include equal stress, LCN, and FAA approaches. ESAL quantifies the effect of varying axle loads as a number of standard single axle loads. Factors like thickness and subgrade reaction are considered. Cars have minimal impact compared to trucks and buses.
This document discusses various aspects of railway track design including gradients, horizontal and vertical curves, super-elevation, and transition curves. It provides formulas for calculating ruling gradient, super-elevation, safe speeds on curves, and other key design elements. Track must be designed to suit the loads and speeds of trains based on safety and economic standards. Proper gradient, curvature, and super-elevation are necessary for smooth train operation.
Overview:
The vertical alignment of a road consists of gradients(straight lines in a vertical plane) and vertical curves. The vertical alignment is usually drawn as a profile, which is a graph with elevation as vertical axis and the horizontal distance along the centre line of the road as the the horizontal axis.
This document discusses horizontal curves in surveying. It covers the objectives of learning about horizontal curve layout, types of curves like simple, compound, and reverse curves. It defines degree of curve and how it is calculated based on the arc or cord length. It describes the elements of a circular curve like point of curvature, point of tangency, radius, chord length, and central angle. Methods for laying out a circular curve are discussed, including linear methods using offsets and bisection, and angular methods like Rankine's method and two theodolite method. Key questions about why curves are needed and defining the degree of curve are also answered.
Signalized Intersections (Transportation Engineering)Hossam Shafiq I
This document provides an overview of signalized intersection analysis and optimization for a transportation engineering course. It defines key terms related to signal timing, describes methods for calculating vehicle delay under uniform and random traffic arrivals, and approaches for optimizing cycle length, green time allocation, and level of service. Examples are provided to illustrate calculations for critical lane group volume-to-capacity ratio, total lost time, optimal signal timing, green time distribution, and intersection level of service.
The document discusses the reasons for and methods of calculating the widening of pavements on horizontal curves. There are two types of widening: mechanical widening to account for vehicle off-tracking due to rigid wheel bases, and psychological widening to allow for greater driver maneuverability at higher speeds. Mechanical widening is calculated based on number of lanes, vehicle wheel base length, and curve radius. Psychological widening is also based on design speed and curve radius. The total widening is the sum of mechanical and psychological widening. Tables from the Indian Road Congress provide extra width recommendations for single and double lane pavements on curves.
Alignment: The position or the layout of the central line of the highway on the ground is called the alignment.
Highway Alignment includes both
a) Horizontal alignment includes straight and curved paths, the deviations and horizontal curves.
b) Vertical alignment includes changes in level, gradients and vertical curves.
This course provides an introduction to transportation engineering through five modules: transportation systems engineering, transportation planning, geometric design, pavement design, and traffic engineering. The objectives are to present a systems approach to transportation and describe the basic characteristics and models used in transportation planning, geometric design of highways, pavement design, and traffic engineering parameters and controls. The course aims to give students an overview of the interactions within transportation systems and the engineering concepts used in their planning, design, and operation.
This document discusses the key considerations for geometric design of highways. It covers standards for rural and urban roads, including lane widths, shoulders, sidewalks and bike lanes. It also discusses elements of horizontal and vertical alignment like curvature, sight distances, super elevation, transitions curves and gradients. Special considerations for designing highways through hilly terrain include ensuring stable slopes, adequate drainage, meeting geometric standards and minimizing unnecessary rises and falls in the road.
Geometric design of tracks aims to provide smooth and safe running of trains at maximum speed while carrying heavy loads. This involves proper design of gradients, curvature, and super elevation (cant).
There are different types of gradients - ruling gradient which is the maximum gradient permitted, momentum gradient which is steeper and uses train momentum, and pusher gradient requiring extra locomotives. Gradients are designed considering train performance and load. Curvature introduces greater resistance requiring grade compensation of ruling gradients.
Super elevation (cant) involves raising the outer rail on curves to counteract centrifugal forces. Equilibrium cant provides equal wheel load distribution. Higher speeds result in cant deficiency which must be limited for passenger safety. Contrary flexures like
Freeway & Highway LOS (Transportation Engineering)Hossam Shafiq I
This document discusses methods for determining freeway and highway level of service (LOS). It defines key terms like free-flow speed, passenger car equivalents, and LOS criteria. The document outlines how to calculate the free-flow speed by measuring it or using a baseline adjusted for factors like lane width. It also explains how to determine the traffic flow rate and convert volumes to passenger cars per lane per hour. Finally, it shows how to use the speed-flow curve and density to establish the LOS for a basic freeway segment based on traffic conditions.
This presentation deals with all the major steps involved in the survey, selection of the most possible route and the designing of the highway.
It will brief u on all the major topics of highway designing
This document discusses vertical alignment in road design. It defines vertical alignment as the vertical aspect of the road profile, including crest and sag curves. It describes the basic components of vertical alignment as grade and vertical curves. Grade is the slope of the road expressed as a percentage, while vertical curves are parabolic curves that provide gradual transitions between different grades to allow comfortable driving. The document discusses types of vertical curves such as sag curves at the bottom of hills and crest curves at the tops of hills, as well as symmetrical and unsymmetrical curves. It provides the equations used to design different types of vertical curves.
Mass-haul diagrams (MHDs) are used to calculate cut and fill volumes and estimate material hauling needs for construction projects. MHDs graphically display cumulative cut and fill volumes along the project centerline. They are used to determine balancing points where cut and fill volumes offset, how much material needs to be imported or exported, and the most economical hauling methods. An example MHD analysis identifies a project's maximum haul distance and calculates how much borrow material is needed to make up the excess fill volume.
Highway geometric design deals with dimensions and layout of visible features like horizontal and vertical alignments, sight distances, and intersections. Elements of geometric design include cross section, sight distance considerations, horizontal and vertical alignments, and intersections. Cross section elements comprise pavement characteristics, carriageway width, cross slope, median/separator, kerbs, road margins, and formation width. Horizontal alignment design considers factors like design speed, horizontal curves, super elevation, transition curves, pavement widening on curves, and setback distance. Super elevation is provided to counteract centrifugal forces on curves and is limited to a maximum of 7% as per Indian standards.
This document provides information on the geometric design of highways. It discusses the key elements of highway design including the width of the carriageway and roadway, right of way, shoulders, side slopes, medians, and design speed. The objectives of geometric design are to optimize efficiency, safety, and cost while minimizing environmental impacts. Standard widths and specifications for elements like carriageways, medians, and shoulders are provided based on highway class and roadway conditions.
A highway pavement is a structure consisting of superimposed layers of processed materials above the natural soil sub-grade, whose primary function is to distribute the applied vehicle loads to the sub-grade. The pavement structure should be able to provide a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics, and low noise pollution.
This document discusses railway turnouts. It begins by defining a turnout as the combination of points and crossings that allows a train to move from one track to another, either parallel or diverging. It then describes the key components of a turnout, including tongue rails, stock rails, lead rails, and a vee crossing. It also explains the classification of turnouts as left-hand or right-hand depending on the direction of diversion. Diagrams are included to illustrate the components and working principle of a turnout. The document concludes by stating that turnouts are essential for diverting traffic but can cause issues if not designed and maintained properly.
Vertical alignment of highway (transportation engineering)Civil Zone
Vertical curves are used in highway design to gradually transition between two different slopes or grades. There are two main types - crest vertical curves, which are used on roadway tops, and sag vertical curves, which are used on dips. The minimum length of a vertical curve is determined based on providing the required stopping sight distance for a given design speed. Additional criteria like passenger comfort, drainage, and appearance may also influence the curve length selected. Longer vertical curves generally provide a smoother ride but require more construction costs.
Railway Engineering-Curves and superelevationMani Vel
This document discusses curves and superelevation on railways. It defines horizontal and vertical curves, and explains that superelevation involves raising the outer rail on a curve to provide a comfortable ride. Superelevation counters the effects of lateral forces when negotiating a curve. The key points are:
- Superelevation is the difference in height between the inner and outer rails and helps distribute load on both rails.
- Equilibrium speed is when the centrifugal force is balanced by the cant (superelevation), providing no unbalanced radial acceleration.
- Maximum permissible speed considers factors like radius, cant, cant deficiency/excess, and transition length.
- Examples are provided to calculate supere
The document discusses the geometric design of roads, specifically horizontal curves. It covers key elements of geometric design like alignment, profile, and cross-section. Horizontal curve design is an important part that influences safety and efficiency. Parameters like design speed, superelevation, extra widening, and minimum radius are discussed in detail according to Indian Road Congress standards. Methods for building superelevation and effecting widening on curves are also summarized.
Determining equivalent single wheel load.(ESWL) Imran Nawaz
This document discusses methods for determining equivalent single wheel loads (ESWL) and equivalent single axle loads (ESAL) for pavement design. ESWL is defined as the load from a single tire that causes the same stresses/strains as a multi-wheel load. Methods include equal stress, LCN, and FAA approaches. ESAL quantifies the effect of varying axle loads as a number of standard single axle loads. Factors like thickness and subgrade reaction are considered. Cars have minimal impact compared to trucks and buses.
This document discusses various aspects of railway track design including gradients, horizontal and vertical curves, super-elevation, and transition curves. It provides formulas for calculating ruling gradient, super-elevation, safe speeds on curves, and other key design elements. Track must be designed to suit the loads and speeds of trains based on safety and economic standards. Proper gradient, curvature, and super-elevation are necessary for smooth train operation.
Overview:
The vertical alignment of a road consists of gradients(straight lines in a vertical plane) and vertical curves. The vertical alignment is usually drawn as a profile, which is a graph with elevation as vertical axis and the horizontal distance along the centre line of the road as the the horizontal axis.
This document discusses horizontal curves in surveying. It covers the objectives of learning about horizontal curve layout, types of curves like simple, compound, and reverse curves. It defines degree of curve and how it is calculated based on the arc or cord length. It describes the elements of a circular curve like point of curvature, point of tangency, radius, chord length, and central angle. Methods for laying out a circular curve are discussed, including linear methods using offsets and bisection, and angular methods like Rankine's method and two theodolite method. Key questions about why curves are needed and defining the degree of curve are also answered.
This document discusses sight distance and horizontal curves, superelevation, and transition curves. It provides the following key points:
1. Sight distance must be provided on horizontal curves to avoid obstructions. The middle ordinate equation calculates the maximum distance an obstruction can be from the centerline while maintaining sight distance.
2. Superelevation is used on curves to counteract centrifugal force. It is expressed as a ratio of outer edge height to width. Maximum rates vary from 4-12% depending on conditions.
3. Transition curves like spirals are used between tangents and curves to gradually change the radius. Their minimum length is calculated using equations involving design speed, radius, and rate
The document discusses circular curves and their use in highway and railway alignment. It defines key terms related to circular curves like deflection angle, chord, radius, and introduces different types of horizontal curves - simple circular curves, compound curves, reverse curves, spiral curves, and lemniscate curves. It also discusses vertical curves like valley and summit curves. The document provides formulas to calculate length of tangent, external distance, middle ordinate, length of chord, length of curve, degree of curve, and minimum radius of curvature for circular curves. It includes examples of problems calculating radius, offset distance, and degree of curve given different curve elements.
This presentation constitutes an integral component of a designated course curriculum and is crafted and disseminated for its intended audience. None of the contents within this presentation should be construed as a formal publication on the subject matter. The author has extensively referenced published resources in the preparation of this presentation, and proper citations will be provided in the bibliography upon completion of its development.
Location horizontal and vertical curves Theory Bahzad5
Setting out of works
horizontal and vertical curves
Horizontal Alignment
ØAn introduction to horizontal curve &Vertical curve.
ØTypes of curves.
ØElements of horizontal circular curve.
ØGeometric of circular curve
Ø Methods of setting out circular curve
Ø Setting out of horizontal curve on ground
Ø Vertical curve Definition.
ØElements of the vertical curves.
ØAvailable methods for computing the elements of vertical curves
Types of Curves
1- Horizontal Curves
2- Vertical Curves
Horizontal Curves
are circular curves. They connect tangent lines around
obstacles, such as building, swamps, lakes, change
direction in rural areas, and intersections in urban areas.
-Compound Curve.
-Reverse curve.
-Transition or Spiral Curves.
-Horizontal Curve: Simple circular
curve
-Elements of horizontal curves.
-Formulas for simple circular
curves.
-Properties of circular curves.
example:A horizontal curve having R= 500m, ∆=40°, station P.I=
12+00 ,prepare a setting out table to set out the curve
using deflection angle from the tangent and chord length
method, dividing the arc into 50m stations.
:Example H.W
A Horizontal curve is designed with a 600m radius and is
known to have a tangent of 52 m the PI is Station
200+00 determent the Stationing of the PT?
-PROCEDURE SETTING OUT Practical .
Vertical Curves
Elevation and Stations of main points on the Vertical Curve .
Assumptions of vertical curve projection.
Example: A vertical parabola curve 400m long is to be set
between 2% (upgrade) and 1% (down grade), which meet
at chainage of 2000 m, the R.L of point of intersection of
the two gradients being (500.00 m). Calculate the R.L of
the tangent and at every (50m) parabola.
Thank you all
Prepared by:
Asst. Prof. Salar K.Hussein
Mr. Kamal Y.Abdullah
Asst.Lecturer. Dilveen H. Omar
Erbil Polytechnic University
Technical Engineering College
Civil Engineering Department
This document discusses the geometric design of highways, specifically horizontal alignment. It covers key elements of horizontal alignment including horizontal curves, spiral transitions, sight distance, and super elevation. The purpose of horizontal curves is to provide a change in direction while spirals provide a gradual transition. Design is based on relationships between speed, curvature, side friction, and super elevation to prevent skidding and overturning. Methods for calculating minimum radius and attaining proper super elevation are presented.
Lec 05 Horizontal Alignment (Transportation Engineering Dr.Lina Shbeeb)Hossam Shafiq I
The document discusses horizontal alignment in transportation engineering. It defines horizontal alignment as straight segments connected by circular curves. It describes different types of curves like simple, compound, and reverse curves. It provides formulas to calculate curve length, radius, degree of curve, and sight distance. Examples are given to demonstrate calculating curve length, radius, and minimum sight distance around a curve. Methods for attaining superelevation on curves through pavement revolutions are also summarized.
Curves are used to gradually change the direction of transportation routes like roads, railways and pipelines. They connect straight tangents and are usually circular arcs. There are different types of curves classified based on their shape and connection of tangents like simple, compound, reverse etc. Elements like radius, deflection angle, length of curve, tangent length etc are used to design circular curves. Various surveying methods like Rankine's, two theodolite etc are used to establish curves on the ground based on their elements and principles. Compound curves consist of two simple circular curves bending in the same direction and joining at a common point of compound.
2 Superelevation and Spiral Curve ( by Malyar Talash, Highway Design Manager/...Malyar Talash
This document discusses superelevation and spiral curves for road design. It defines superelevation as banking curves to counteract centrifugal force on vehicles. Maximum superelevation rates are recommended based on climate and road type. Methods for achieving superelevation include rotating the pavement surface. Minimum lengths for superelevation runoff and tangent runoff sections are calculated based on design speed, superelevation rate, and other factors. Spiral curves provide a gradual transition between tangent and curved sections and can be used to achieve superelevation runoff. Equations are provided to calculate minimum and maximum spiral lengths. An example problem demonstrates calculating runoff lengths and locating transition points for a road section both with
The document discusses various aspects of highway engineering related to horizontal and vertical alignment of roads. It describes extra widening needed on curved sections of roads to accommodate vehicles. It discusses the analysis and formulas to calculate mechanical and psychological widening. It also covers horizontal transition curves, their objectives and methods to determine length. The document discusses setback distance for obstructions on curved sections and the formulas to calculate setback based on sight distance and curve length. It concludes with definitions of gradient, ruling gradient and other types for vertical alignment considerations.
3 vertical alignment of road by Malyar TalashMalyar Talash
This document discusses vertical road alignment and provides guidance on vertical curve design. It covers several key topics:
- The influence of topography on vertical alignment and how terrain is classified.
- The two main aspects of vertical alignment: vertical curvature and gradient.
- The two types of vertical curves: crest and sag curves.
- Design considerations for vertical grades and maximum grades based on vehicle type and speed.
- Equations for determining minimum vertical curve lengths to provide adequate sight distance and passenger comfort.
1) Transition curves, also known as spiral curves or easement curves, are used between tangent sections and circular curves to provide a smooth transition between them.
2) They allow for a gradual increase in super elevation or "cant" to balance the centrifugal forces experienced by vehicles on curves. This ensures passenger safety.
3) Common types of transition curves include the clothoid spiral, cubic parabola, and lemniscate. The clothoid spiral is the most widely used as it provides a constant rate of change in curvature.
Chapter 2 track geometrics and its maintainancedhara dattani
1. Proper geometric design of railway tracks is necessary to ensure safe and smooth running of trains at maximum speeds and loads.
2. Key parameters that determine track geometry include gradients, curve radii, superelevation/cant, and horizontal and vertical curves.
3. Most train derailments are caused by track defects like defective cross-levels, alignments, gauge, joints, superelevation, curve radii, and switch wear.
This document discusses methods for designing horizontal curves on roadways. It covers topics such as superelevation, spiral transitions, and methods for calculating runoff lengths. Superelevation is the banking of a road through a curve to help vehicles negotiate the turn. Runoff lengths refer to the distances needed to transition from normal crown to full superelevation. Spiral transitions provide a gradual path for vehicles entering and exiting a curve. Formulas are provided to calculate minimum and maximum spiral lengths based on design speed and curve radius. Examples demonstrate how to determine appropriate locations for transitions on horizontal curves using given design parameters.
This document discusses the design of vertical alignment for roads. It defines vertical alignment as the vertical aspect of the road profile, including crest and sag curves. The two basic elements are grades and vertical curves. Grades refer to the rate of rise or fall, while vertical curves provide transitions between sloped roadways and allow gradual elevation changes. The document outlines the types of gradients and vertical curves, and provides the design parameters and equations for determining the length of summit and valley vertical curves based on sight distance and comfort.
This document provides definitions and explanations of terms related to horizontal curves. It discusses the following:
- Horizontal curves are used to connect two straight lines when there is a change in direction of a road or railway alignment. Circular curves are the most common type of horizontal curve.
- Key terms defined include degree of curve, radius, relationship between radius and degree, superelevation, and centrifugal ratio.
- Different types of horizontal curves are described, including simple circular, compound, reverse, and transition curves.
- Notation used in circular curves is explained, such as tangent points and lengths, deflection angle, and radius.
- Properties of simple circular curves are outlined, including
Curves are used in transportation routes to gradually change direction between straight segments. There are several types of curves including simple, compound, reverse, and transition curves. A simple circular curve connects two tangents with a single arc, and is defined by its radius or degree. Transition curves provide a gradual transition between tangents and circular curves to avoid abrupt changes in grade or superelevation that could cause vehicles to overturn. There are several methods for laying out circular curves, including using offset distances from the long chord between tangent points or measuring deflection angles from the initial tangent.
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3. Both designs satisfy all other limit states checked such as web local yielding, web sidesway buckling, and have sufficient weld strength.
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3. Alignment Of Highways
3
The alignment is the route of the road, defined as a series of horizontal
tangents and curves.
4. Alignment Of Highways
4
Grade Line: is a line or slope used as a longitudinal reference for a
railroad or highway. Inclinations with the horizontal of a road, railroad,
etc., usually expressed by stating the vertical rise or fall as a percentage
of the horizontal distance; slope. Main consideration while selecting
grade line are,
1. Amount of earth work
2. Natural Terrain
3. Minimum sight distance requirement
4. Flood water level
5. Maximum Level of ground water
Profile grade line (PGL) - This is a single line, straight or curved, along
the length of the highway, sometimes but not always on the center of the
highway.
5. Alignment Of Highways
5
The alignment of a highway is composed of horizontal and
vertical elements
The horizontal alignment:
includes the straight (tangent) sections of the roadway
circular curves that connect their change in direction
The vertical alignment:
includes straight (tangent) highway grades
parabolic curves that connect these grades
6. Alignment Of Highways
6
Highway alignment is in reality a three-dimensional
problem
Design & construction is difficult in 3-D so highway design
is typically treated as two 2-D problems: Horizontal
alignment, vertical alignment
7. Alignment Of Highways
7
VerticalAlignment
HorizontalAlignment
Horizontal Alignment
Corresponds to “X” and “Z”
Coordinates
Plan view – Roughly
Equivalent to perspective
view of an aerial photograph
of highway.
Vertical Alignment
Corresponds to highway
length and “Y” coordinate.
Presented in a profile view.
Gives elevation of all points
measured along the of a
highway.
8. Alignment Of Highways
8
• Instead of using the coordinates system, highway positioning and length are
defined as the distance usually measured along the center line of the
highway from a specified point (also called “Reduced Distance” or ‘RD’)
• The notation for stationing distance is such that a point on highway 4250 ft
(1295.3 m) from a specified origin (0+00 or 0+000) is said to be at station:
– 42+50 ft (42 stations and 50 feet)
– I + 295.300 meter( 1 station and 295.300 meters)
9. Alignment Of Highways
9
The horizontal alignment consists of tangents and curves
The curves are usually segments of circles, which have radii
that will provide for a smooth flow of traffic
The critical design feature of horizontal alignment:
horizontal curve that transitions the roadway between
two straight (tangent) sections
focus on the design of directional transition of the
roadway in a horizontal plan
A key concern in the directional transition is the ability of
the vehicle to negotiate the horizontal curve
11. Alignment Of Highways
11
Horizontal alignment to accommodate the cornering capability
of a variety of vehicles (cars to combination trucks)
The design of the horizontal alignment entails the
determination of:
the minimum radius of the curve
determination of the length of the curve
Side friction factor
Superelevation
Adequate stopping sight distance
13. (1) Simple horizontal curve
Horizontal Curves - Types of Curves
o Horizontal Curves: curves used in horizontal planes to connect two
straight tangent sections
o Simple Curve: circular arc connecting two tangents
14. Horizontal Curves
A properly designed transition curve provides a
natural, easy-to-follow path for drivers, such that
the lateral force increases and decreases
gradually as a vehicle enters and leaves a circular
curve.
Transition curves minimize encroachment on
adjoining traffic lanes and tend to promote
uniformity in speed.
A spiral transition curve simulates the natural
turning path of a vehicle.
15. (2) Compound curve
R1
R2
Horizontal Curves
o Compound Curve: a curve which is composed of two or more
circular arcs of different radii, with centers on the same side of the
alignment
o Compound curves are used to fit horizontal curves to very specific
alignment needs …..interchange ramps, intersection curves etc.
o Radii should not be very different- difficult for drivers to maintain
lane position during transition from one to another curve
16. Horizontal Curves - Types of Curves
o Spiral Curve: A curve with constantly changing radius
o a curve whose radius decreases uniformly from infinity at the
tangent to that of the curve it meets
o Motorist usually create their own transition path while moving from
tangent section to curve….spiral curves not often used
o Special case use: used to gradually introduce superelevation
Spiral curve
Horizontal Curves
17. Horizontal Curves - Types of Curves
R1
R2
R1
R2
(4) Reverse Curve
(a) With tangent (b) Without tangent
o Reverse Curve: Two circular arcs tangent to each other, with their
centers on opposite sides of the alignment
o Two consecutive curves that turn in opposite direction
o Not recommended- drivers may find it difficult to stay in their lane
as a result of sudden change in alignment
Horizontal Curves
18. Horizontal Curves - Types of Curves
o Easement Curves: curves used to lessen the effect of the sudden
change in curvature at the junction of either a tangent and a
curve, or of two curves.
Horizontal Curves
19. Properties of Circular Curves
Degree of Curvature
• Traditionally, the “steepness” of the curvature is defined by either the
radius (R) or the degree of curvature (D)
• In highway work we use the ARC definition
• Degree of curvature = angle subtended by an arc of length 100 feet
Horizontal Curves
20. Properties of Circular Curves
o Degree of curvature = angle subtended by an arc of length 100 feet
o By simple ratio: D/360 = 100/2*Pi*R
Therefore
R = 5730 / D
o D = Degree of curvature - degrees
o R = Radius of curvature - feet
Horizontal Curves
21. o Length of Curve:
The length of the curve derives directly from the
arc definition of degree of curvature
o A central angle equal to the degree of curvature
subtends an arc of 100 ft, while the actual central
angle (Δ) subtends the length of the curve (L).
o By simple ratio
D/100=Δ/L
L = 100 Δ / D
o Or (from R = 5730 / D, substitute for D = 5730/R)
o L = Δ R / 57.30
o (note: D is not Δ – the two are often confused )
Horizontal Curves
22. Horizontal Curves Fundamentals -Layout
R = Radius of Circular Curve (ft)
PC = Point of Curvature
(Beginning of Curve)
PT = Point of Tangency
(End of Curve)
PI = Point of Intersection
T = Tangent Length
(T = PI – PC)
L = Length of Curvature
(L = PT– PC)
M = Middle Ordinate
E = External Distance
L.C = Chord Length
Δ = Deflection Angle or
external angle
23. Useful Formulas…
o Tangent: T = R tan(Δ/2)
(Triangle143)
o Chord: L.C = 2R sin(Δ/2)
(Triangle 364)
o Mid Ordinate: M = R – R cos(Δ/2)
o External Distance: E = R sec(Δ/2) - R
Horizontal Curves Fundamentals -Layout
24. Deflection angle of a 4º curve is 55º25’, PI at station
245+97.04. Find length of curve,T, and
station of PT.
D = 4º , = 55º25’ = 55.417º
R
D
5729.58
R
5729.58
1432.3ft.
4
Horizontal Curves Fundamentals -Layout
25. Horizontal Curves – Example1
D = 4º
= 55.417º
R = 1,432.4 ft
L = 2R
360
= 2(1,432.4 ft)(55.417º) = 1385.42ft
360
26. Horizontal Curves – Example1
D = 4º
= 55.417º
R = 1,432.4 ft
L = 1385.42 ft
T = R tan = 1,432.4 ft tan (55.417) = 752.29 ft
2 2
27. Horizontal Curves – Example
A horizontal curve is designed with a 2000-ft radius. The curve has a
tangent length of 400 ft. and the PI is at station 103 + 00. Determine
the stationing of PT
Formulas…
o Tangent: T = R tan(Δ/2)
(Triangle 143)
o Chord: L.C = 2R sin(Δ/2)
(Triangle 364)
o Mid Ordinate: M = R – R cos(Δ/2)
o External Distance: E = R sec(Δ/2) - R
Horizontal Curves – Example 2
29. 29
o The presence of horizontal curve imparts centrifugal force which is a
reactive force acting outward on a vehicle negotiating it
o Centrifugal force depends on speed and radius of the horizontal
curve and is counteracted to a certain extent by transverse friction
between the tyre and pavement surface
o On a curved road, this force tends to cause the vehicle to overrun or
to slide outward from the center of road curvature
o For proper design of the curve, an understanding of the forces
acting on a vehicle taking a horizontal curve is necessary.
o From the basic laws of physics ….centrifugal force is as:
Concept of Super-elevation
31. Super-elevation
31
Forces acting on a vehicle on horizontal curve of radius R (m) at a speed of V m/sec^2
P = centrifugal force acting horizontally out-wards through the center of gravity
W = weight of the vehicle acting down-wards through the center of gravity, and
F = friction force between the wheels and the pavement, along the surface inward
33. Super-elevation
33
• The exact expression for superelevation
• For small ϴ (ϴ < 4 degrees and f=0.15 (generally) )
o 1- f tan ϴ = 1 (f tan ϴ =0)
o tan ϴ = ϴ = e ……………..above expression can be written as
V 2
0.01e f
gR
e = rate of roadway superelevation, percent (number of vertical feet of rise per 100 feet
of horizontal distance)
f = side friction factor
g = gravitational constant
V = vehicle speed
R = radius of curve measured to a vehicle’s center of gravity
34. Super-elevation
34
e = rate of roadway superelevation, %
f = side friction (demand) factor
v = vehicle speed, m/s
g = gravitational constant, 9.81 m/s2
V = vehicle speed, Kmph
R = radius of curve measured to a
vehicle’s center of gravity, meter
e = rate of roadway superelevation, %
f = side friction (demand) factor
v = vehicle speed, ft/s
g = gravitational constant, 32.2 ft/s2
V = vehicle speed, mph
R = radius of curve measured to a
vehicle’s center of gravity, ft
• AASHTO expression for superelevation after
simplification
35. Superelevation Example -1
35
A roadway is being designed for a speed of 70 mi/h. At one
horizontal curve, it is known that the superelevation is 8.0% and
the coefficient of side friction is 0.10. Determine the minimum
radius of curve (measured to the traveled path) that will provide
for safe vehicle operation
36. Superelevation Example -2
36
Determine the proper superelevation rate for an urban highway with a
design speed of 50 mph and degree of curvature of 8 degrees
Super elevation Examples
37. Superelevation Example -3
A 1.0-km long racetrack is to be designed with turns 250 m in length
at each end. Determine the superelevation rate you would
recommend for a design speed of 130 km/h.
37
Super elevation Examples
38. Maximum Super-elevation
38
o The maximum rates of superelevation:
o Climate conditions: (i.e., frequency and amount of snow and ice)
o Terrain conditions (i.e., flat, rolling, or mountainous)
o Type of area (i.e., rural or urban)
o Frequency of very slow-moving vehicles whose operation might
be affected by high superelevation rates
o No single maximum superelevation rate is universally applicable
o Design consistency: Using only one maximum superelevation rate
within a region of similar climate and land use is desirable
39. Maximum Super-elevation
39
o AASHTO recommendation:
o 4% and 12%
o Increments of 2%
o Maximum rates adopted vary from region to region
– 12% - maximum superelevation rate. Drivers feel uncomfortable
on sections with higher rates, and driver effort to maintain lateral
position is high when speeds are reduced on such curves
– Snow and Ice Conditions:
• 8% is generally used
• Ice on the road can reduce friction force and vehicle travelling
at less than the design speed on the excessively
superelevated curve slide inward off the curve due to
gravitational forces
– Urban areas: 4%-6%
– Low-speed urban streets or at intersections: may be eliminated
40. Minimum Super-elevation
40
o It should be noted that on open highway sections, there is generally
a minimum superelevation maintained, even on straight sections
o This is to provide for cross drainage of water to the appropriate
roadside(s) where sewers or drainage ditches are present for
longitudinal drainage
o This minimum rate is usually in the range of 1.5% for high-type
surfaces and 2.0% for low-type surfaces.
43. Side-Friction Factor
43
o With the wide variation in vehicle speeds on curves, there usually is
an unbalanced force whether the curve is superelevated or not.
o This force results in tire side thrust, which is counterbalanced by
friction between the tires and the pavement surface
o This frictional counterforce is developed by distortion of the contact
area of the tire
o The upper limit of the side friction factor is the point at which the
tire would begin to skid; this is known as the point of impending
skid
o Because highway curves are designed so vehicles can avoid skidding
with a margin of safety, the “f” values used in design should be
substantially less than the coefficient of friction at impending skid
44. Side-Friction Factor
44
o Important factors affecting side friction factor at impending skid:
o speed of the vehicle (f decreases as speed increases (less
tire/pavement contact))
o the type and condition of the roadway surface
o type and condition of the vehicle tires
o Design values represent wet pavements and tires in reasonable but
not top condition
o Values also represent frictional forces that can be comfortably
achieved; they do not represent, for example, the maximum side
friction that is achieved the instant before skidding
o Design values for the coefficient of side friction (f) vary with speed
from 0.38 at 10 mph to 0.08 at 80 mph
46. OFFFF
Off Tracking
46
Off tracking is the characteristic, common to all vehicles, although
much more pronounced with the larger design vehicles, in which the
rear wheels do not precisely follow the same path as the front wheels
when the vehicle traverses a horizontal curve or makes a turn.
At slow speed, off track inward
At higher speeds, the rear wheels may even track outside the
front wheels.
47. Curve Widening
47
On horizontal curves , especially when they are not of very
large radius, it is a common practice to widen the pavement
slightly more than the normal width, the object of providing Extra
Widening of pavements on horizontal curves are due to the
following reasons....
(a) An automobile such as car, bus or truck has a rigid wheel base
and only the front wheels can be turned. When the vehicle
takes a turn to negotiate a horizontal curve, the rear wheels do
not follow the same path as that of the front wheels. This
phenomenon is called ‘off tracking’. The off tracking depends
on
(1) the length of the wheel base of the vehicle
(2) the turning angle or the radius of the horizontal curves.
48. Curve Widening
48
(b) At more than design speed if super elevation and lateral
friction jointly cannot counteract the centrifugal force, full
outward slipping of rear wheels may occur and thus more width
of road is covered. This condition occurs at very high speeds.
(c) At start of the curves drivers have a tendency to follow outer
edge of the pavement to have better visibility and large radius
curved path. This also necessitates extra width of the road.
(d) Trailer units require even larger extra width at curves.
49. Curve Widening
49
Analysis of extra widening on horizontal curves
The extra widening of pavement on horizontal curves is
divided into two parts
(i) Mechanical widening and
(ii) Psychological widening.
Here,
n =number of traffic lanes
l = length of wheel base of longest vehicle in m
R= radius of horizontal curves in m
The widening required to account for the off tracking due
to the rigidity of wheel base is called ‘Mechanical widening ‘.
50. Curve Widening
50
(ii) Psychological widening :-
At horizontal curves driveres have a tendency to maintain a
greater clearance between the vehicles than on straight stretches of
road. Therefore an extra width of pavement is provided for
psychological reasons for greater manoeuvrability of steering at
higher speeds and to allow for the extra space requirements for the
overhangs of vehicles. Psychological widening is therefore
important in pavements with more than one lane. An empirical
formula has been recommended byt IRC for deciding the additional
psychological widening ‘Wps’ which is dependent on the design
speed, V of the vehicle and the radius. R of the curve. The
psychological widening is given by the formula:
51. Curve Widening
51
Hence the total widening Werequired on a horizontal curve is
given by:
Here,
n =number of traffic lanes
l = length of wheel base of longest vehicle in m
R= radius of horizontal curves in m
V= design speed Kmph
53. Sight Distances
53
Sight distance is the length of the road way
section visible to the road user.
A driver’s ability to see ahead is needed for safe and
efficient operation of a vehicle on a highway.
For example, on a railroad, trains are confined to a
fixed path, yet a block signal system and trained
operators are needed for safe operation.
54. Sight Distances
54
The designer should provide sight distance of sufficient
length that drivers can control the operation of their
vehicles to avoid striking an unexpected object in the
traveled way.
Sight distance is the distance along a roadway throughout
which an object of specified height is continuously visible to
the driver.
This distance is dependent on the height of the driver’s eye
above the road surface, the specified object height above
the road surface, and the height and lateral position of sight
obstructions within the driver’s line of sight
55. Sight Distances
55
Criteria For Sight Distances
Height of Driver’s Eye
For all sight distances calculations the height of the driver’s eye is
considered to be 1.08 m [3.50 ft.] above the road surface. This value is based on a
study (17) that found average vehicle heights have decreased to 1.30 m [4.25 ft.]
with a comparable decrease in average eye heights to 1.08 m [3.50 ft.].
For large trucks, the driver eye height ranges from 1.80 to 2.40 m [3.50
to 7.90 ft]. The recommended value of truck driver eye height for design is 2.33 m
[7.60ft] above the road surface.
Green Book (AASHTO,2011)
Height of Object
For stopping sight distance and decision sight distance calculations,
the height of object is considered to be 0.60 m [2.00 ft] above the
road surface. For passing sight distance calculations, the height of
object is considered to be 1.08 m [3.50 ft] above the road surface.
Green Book (AASHTO,2011)
56. Sight Distances
56
Stopping Sight Distance (SSD)
It is the minimum required distance by a drive travelling at a
given speed to stop vehicle after seeing an object on
highway from a specific height.
Two most important driver characteristics
Visual and hearing perceptions
Perception-Reaction Process
58. Sight Distances
58
Perception
Sees or hears situation (sees deer)
Identification
Identify situation (realizes deer is in road)
Emotion
Decides on course of action (stop, change lanes, etc)
Reaction (volition)
Acts (time to start events in motion but not actually do
action)
Foot begins to hit brake, not actual deceleration
59. Sight Distances
59
PRT is important factor:
Determination of braking distances
Establishing minimum sight distance on highway
Length of the yellow phase at a signalized intersection
Typical Perception-Reaction time range - 0.5 to 7 seconds
For stopping sight distance - AASHTO recommends 2.5 sec
PRT
60. Sight Distances
60
Perception-Reaction Time Factors
Environment (Urban vs. Rural, Night vs. Day, Wet vs. Dry)
Driver Age
Physical Condition
Medical Conditions (Visual Acuity)
Complexity Of Situation
Expected v/s Unexpected
Distractions
61. Sight Distances
61
Perception-Reaction Process –Reaction Distance
Stopping Sight Distance (SSD) - Length of the roadway ahead that is
visible to the driver or the distance along a roadway throughout which an
object of specified height is continuously visible to the driver.
Composed of Two Parts
Distance traveled during perception/reaction time
Distance required to physically brake vehicle
SSD = PRD + BD
PRD = dr = 1.47(Vi)(t)
dr = Distance traveled during PRT(feet)
Vi = velocity (mph),
t = PRT= 2.5s (generally)
65. Sight Distances
65
Use basic assumptions to determine SSD at 60 mph on
and a=11.2 ft/s
a) 0% grade, b) 3% grade
(a) G 0% b) 3% grade
2
Effect Of Gravity On BD
66. Sight Distances
66
Passing Sight Distance (PSD)
The passing sight distance is the minimum sight
distance required on a two-lane, two way
highway that will permit a driver to complete a
passing maneuver without colliding with an
opposing vehicle and without cutting off the
passed vehicle
68. Sight Distances
68
d(1) = distance traversed during perception and reaction time and during the
initial acceleration to the point of encroachment on the rightlane
d(2) = distance traveled while the passing vehicle occupies the rightlane
Passing Sight Distance (PSD)
69. Sight Distances
69
d(3) = distance between the passing vehicle at the end of its maneuver and the
opposing vehicle
d(4) = distance traversed by the opposing vehicle for two-thirds of the time the
passing vehicle occupies the right lane
Passing Sight Distance (PSD)
71. Sight Distances
71
Decision Sight Distance
Decision sight distance is the distance required for a
driver to:
Detect an unexpected or otherwise difficult-to-perceive
information source or hazard in a roadway environment
hazard may be visually cluttered
recognize the hazard or its potential threat
select an appropriate speed and path
initiate and complete the required safety maneuver
safely and efficiently
72. Sight Distances
72
Where to Provide…….?
AASHTO recommends that decision sight distance be
provided
At interchanges or intersection locations where
unusual or unexpected maneuvers are required;
Changes in cross-section such as lane drops and
additions, toll plazas, and intense-demand areas
where there is a substantial ‘visual noise’ from
competing information (e.g. control devices,
advertising roadway elements)
One factor that significantly influences the selection of a highway location is the terrain the land, which in turn affects the laying of the grade line. The primary factor that the designer considers on laying the grade line is the amount of earthwork that will be necessary for the selected grade line. The height of the grade line is usually dictated by expected floodwater level. Grade lines should also be set such that the minimum sight distance requirements are obtained.
Maximum grade - Maximum grade is determined by a table, with up to 6% allowed in mountainous areas and hilly urban areas.
In vehicular engineering, various land-based designs (cars, SUVs, trucks, trains, etc.) are rated for their ability to ascend terrain. (Trains typically rate much lower than cars.) The highest grade a vehicle can ascend while maintaining a particular speed is sometimes termed that vehicle's "gradeability" (or, less often, "grade ability").