Geometric Design of Highways and cross section- 1.ppt
- 2. Geometric Design of Highways & Design Criteria
- 3. There are two types of highway design: Structural design Geometric design Introduction
- 4. The structural design deals with the design of the pavement structure. The geometric design of roads concerned with the positioning of the physical elements of the roadway according to standards. The basic objectives in geometric design are to optimize efficiency and safety while minimizing cost and environmental damage. Introduction
- 5. Structural Design. The goal of structural design is to determine the number, material composition and thickness of the different layers within a pavement structure required to accommodate a given loading regime. This includes the surface course as well as any underlying base or subbase layers This design includes different types of tests on road pavements and materials used in road i.e CBR test, Classifications and analysis. Introduction
- 6. whereas geometric design deals with the dimensions and layout of visible features of the highway such as; (1) cross-section elements, (2) alignment, (3) sight distances and (4) Intersections. Introduction
- 7. A geometric design saved on construction costs and improved visibility with the intention to reduce the likelihood of traffic incidents. Introduction to Geometric Design
- 8. Geometric roadway design can be broken into three main parts: alignment, profile, and cross-section. Combined, they provide a three-dimensional layout for a roadway. The alignment is the process of locating the route of the road, defined as a series of straight paths and curves. Horizontal curves are used to negotiate a sudden change in a direction or to avoid the obstruction. Introduction to Geometric Design 1. Plan View Horizontal Alignment
- 9. The profile of a road shows change in elevation, consists of road slopes, called grades, connected by parabolic vertical curves. Vertical curves are used to provide a gradual change from one road slope to another, so that vehicles may smoothly navigate grade changes as they travel. Introduction to Geometric Design 2. Profile View Vertical Alignment
- 10. The cross section shows the position and number of vehicle and bicycle lanes and sidewalks, along with their cross slope or banking. Cross sections also shows other cross sectional elements i.e. shoulders, median, curbs etc and drainage features. Introduction to Geometric Design Cross section of the highway - lanes, shoulders and medians
- 11. Design standards Roads are designed in conjunction with design guidelines and standards. These are adopted by national and sub-national authorities (e.g., states, provinces, territories and municipalities). Design guidelines take into account speed, vehicle type, road grade (slope), view obstructions, and stopping distance. With proper application of guidelines, along with good engineering judgement, an engineer can design a roadway that is comfortable, safe, and appealing to the eye. The primary US guidance is found in A Policy on Geometric Design of Highways and Streets ”AASHTO Green Book” published by the American Association of State Highway and Transportation Officials (AASHTO). Other standards include the Australian Guide to Road Design, and the British Design Manual for Roads. Introduction to Geometric Design
- 12. AASHTO Green Book and Geometric Design
- 13. AASHTO Green Book • What the Green Book Contains Its official title is “A Policy on the Geometric Design of Highways and Streets.” Published by the AASHTO since the late 1930's with the most recent edition issued in 2011. It has series of guidelines on geometric design within which the designer has a range of flexibility. .
- 15. Geometric Design. Geometric design needs to fulfill the requirements of the driver and the vehicle, such as comfort, efficiency and safety. The geometric design includes curves i.e. horizontal curves, vertical curves and specific design elements of a highway, such as • the number of lanes, • lane width, • median type and width, • length of freeway acceleration and deceleration lanes, • need for truck climbing lanes for highways on steep grades, and • radii required for vehicle turning. Introduction to Geometric Design
- 16. Dedicated acceleration lanes allow cars that are joining the main road to speed up to match the flow of traffic. Deceleration lanes allow traffic exiting a major street to slow down to a safer speed to make a left or right turn at an intersection without affecting the main flow of traffic. Introduction to Geometric Design
- 17. Introduction to Geometric Design
- 18. Climbing Lanes Introduction to Geometric Design
- 19. Introduction to Geometric Design
- 20. Introduction to Geometric Design Emphasis of the geometric design – Needs of the driver and the vehicle such as safety, comfort, efficiency, etc. Features considered: Cross section elements Sight Distance Transverse slope and gradients Alignment (Horizontal and Vertical) Intersections
- 21. Introduction to Geometric Design
- 22. Factors Affecting Geometric Design of Highway
- 23. The geometric design depends on several factors such as: Design speed Topography of the surrounding land Classification of the roadway Traffic volume and composition Capital costs for construction Vehicle size and performance characteristics Factors Affecting Geometric Design
- 24. All these elements and the performance characteristics of vehicles play an important role. Physical dimensions of vehicles affect a number of design elements such as the radii required for turning Height of highway overpass Lane width Factors Affecting Geometric Design
- 25. Factors Affecting Geometric Design •Design speed & Design vehicle The maximum safe speed that can be maintained over a section of highway when conditions are so favorable that the design features of the highway govern. Design Speed depends on the functional classification of the highway (expected traffic volume), the topography of the area and the adjacent land use.
- 26. Factors Affecting Geometric Design
- 27. Factors Affecting Geometric Design •Design speed & Design vehicle
- 28. Factors Affecting Geometric Design Topography of the area that the highway traverses
- 29. Factors Affecting Geometric Design •Human characteristics
- 30. Factors Affecting Geometric Design Cross section of the highway - lanes, shoulders and medians
- 31. Factors Affecting Geometric Design Presence of heavy vehicles on steep grades
- 32. Factors Affecting Geometric Design Level of service
- 33. Factors Affecting Geometric Design Economy - Available funds
Editor's Notes
- #15: Deceleration lanes allow traffic exiting a major street to slow down to a safer speed to make a left or right turn at an intersection without affecting the main flow of traffic. Dedicated acceleration lanes allow cars that are joining the main road to speed up to match the flow of traffic.