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PART I GEOMETRIC DESIGN OF HIGHWAYS

PART I GEOMETRIC DESIGN OF HIGHWAYS. The Egyptian road network was divided into three categories: 1- divided highways; 2- main roads; which consists of: -1 st.class roads; -2 nd class roads; -3 th class roads 3- regional (local) roads. CHAPTER 1 INTRODUCTION.

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PART I GEOMETRIC DESIGN OF HIGHWAYS

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  1. PART I GEOMETRIC DESIGN OF HIGHWAYS

  2. The Egyptian road network was divided into three categories: 1- divided highways; 2- main roads; which consists of: -1 st.class roads; -2 nd class roads; -3 th class roads 3- regional (local) roads. CHAPTER 1INTRODUCTION

  3. 1. Divided Roads: usually link up Cairo with large cities or main ports. These roads consists of four lane divided highway. They are as follows: -Cairo -Alexandria of length 193 km; -Cairo -Alexandria desert road of length 200 km; -Cairo -Esmaillia with length 130 km; -Giza -El Marazic with length 23 km; -Tanta- El Mahallah with length 22 km.

  4. 2.First class Roads: These roads connect the capital of provinces or big cities together. Normally consists of two lanes with lane width 3.75 m. Average daily traffic ranges between 3000 to 6000 veh./day. 3.Second class roads: Connecting cities in provinces and having traffic volume ranging from 1000 to 3000 veh./day, and consists of two lanes each being 3.0 m width.

  5. 4. Third class roads: These roads link up villages and the social activity center with the road network. It usually carries 200 to 1000 veh./day and total width ranges from 5.0 to 6.0 m. 5.Local roads:  Connecting villages to main roads or cities, and having traffic volume <1000 veh./day. and is divided into two classes: Paved surface roads: Traffic volume ranging from 200-1000 veh./day , with paved width of 4.0 m. Unpaved roads: Normally constructed of gravel as well as crush stone or stabilized soil. Volume of traffic is less than 200 veh./day.

  6. CHAPTER 2DESIGN CONTROLS AND CRITERIA FOR GEOMETRIC DESIGN

  7. The design elements of highway is influenced by: a) Highway system and classification; b) Topography and environment features; c) Traffic volume characteristic; d) Speed of vehicles; e) Traffic capacity.

  8. Highway Systems and Classification: The major classifications may be as follows: Rural a.Freeway (expressway) b.Major highway c.Local road Urban a.Freeway b.Major (arterial) street; c.Local street

  9. Topography and environment features: The topography, physical features and land use of the area affect the highway geometric design elements. The design elements in rough and hilly areas may be affected much as in flat areas, but the drainage design in hilly areas is considerably influenced. Topography sometimes decides the type of highway. For example, steep grades and restrictive sight distance affect the capacity of 2-lane highway. Land use has a significant effect on highway geometric. For example, rural highways are generally designed for high speeds whereas urban highways near cities for lower speeds, more turning movements, better and frequent intersections, and construction of parking lots.

  10. Traffic: characteristic that influence the geometric design of a highway include : traffic volume, composition and speed. Traffic volume affects the capacity and consequently the number of lanes required. Average daily traffic (ADT) is the general unit of measure for traffic volume and it is define as the total volume during a given time period (>1day, and < 1year), divided by the number of days in that time period. ADT = Total traffic volume in one year / 365

  11. For design purposes and planning, the demand of traffic is generally expressed in terms of the Design-Hourly Volume (DHV), predicted on a design year usually after 20 years. Hourly traffic volumes during a year generally ranges from 0.16 to 0.34 ADT with an average value of 0.26 ADT. Fig.(1) shows the relation between highest hourly volumes and ADT on main rural highway. Generally DHV is representative of the 30 th. highest hourly volume of the year.

  12. -Relation between DHV and ADT: The DHV may be expressed as a percentage of the ADT .( k = DHV/ADT ) , on rural highways , values of k ranges between 0.12 to 0.18 with an average value of 0.15. On urban highways, the factor k ranges from 0.08 to 0.16 with an average value of 0.12.

  13. -Directional Distribution (D):  Usually to measure traffic for 2-lane highway using the design hourly volume as the total traffic in both directions of travel. Knowledge of the hourly traffic load in each direction of travel for highway with more than 2-lanes is essential for design. In some cases, traffic may be split 50-50 as two directions, but during most peak-hour periods it is common to find a larger percentage of traffic movement in one direction.

  14. -Traffic Compositions: For design purposes, the percentage of truck traffic during the peak hours must be determined. The average value of (T) expressed as percentage of DHV is 10 -20 % . Design Vehicle:  The dimensions of the motor vehicle influence design practice. The width of the vehicle naturally affects the width of the traffic lane , vehicle length has a bearing on roadway capacity and affects the turning radius, the height of the vehicle affects the clearance of the various structures.

  15. Speed: • The speed adopted by a driver depends upon four general conditions: • The physical characteristics of the highway and its roadsides. • 2.The weather. • 3.The presence of other vehicles. • 4.The speed limitation.

  16. Design Speed: Design speed that could be used in Egypt ranging from 20 km/h for one lane paved route for light loading (10 v/h) to 100 km/h for class I Expressway ( as Cairo -Alex. expressway), or class I with maximum capacity of 500 v/h.

  17. Running Speed: The running speed is the speed of the vehicle over a specified section of highway, being the distance divided by running time (the time of motion). It ranges usually from 0.75 to 0.90 of the design speed. Spot Speed: One means of obtaining an equivalent average running speed on an existing facility where flow is reasonably continuos is to measure the spot speed. The average spot speed is the arithmetic mean of the speeds of all traffic at a specified point.

  18. Traffic Capacity Highway capacity indicates the ability of a roadway to accommodate traffic. Basic capacity: It is the maximum number of passenger cars that can pass a given point on a lane or roadway during one hour under the most nearly ideal roadway and traffic conditions that can be attained.

  19. The ideal conditions are as follows: • 1. There must be at least 2-lanes for each • direction; • 2.All vehicles must be moved at approximately the same speed; • 3.There must be practically no commercial • vehicle; • 4.The width of traffic lane , shoulders, and clearances to vertical obstructions beyond the edge of the traffic lane must be adequate; • 5.There must be no restrictive sight distances, grades, and improperly superelevation curves.

  20. The basic capacity for 4-or multi-lane highways is 2000 P.cars /lane/h. While for 2-lane highways, it is 2000 p.cars/h in both directions. Possible capacity: It is the maximum number of vehicles that can pass a given point on a specified lane or roadway during one hour under the prevailing roadway conditions. It is less than the basic capacity because it recognizes the failure of one or more of the five conditions assumed for establishing the basic capacity.

  21. Practical capacity: It is the maximum number of vehicles that can pass a given point on a lane or roadway during one hour under the existing roadway and traffic conditions. Design capacity: It is value equals or less than practical capacity determined for use in designing the highway to accommodate the design volume. This design speeds are considered 70-80 km/h in rural areas and 55-65 km/h in urban areas. To maintain these speeds ,the design capacity must be  DHV and determined on the bases of passenger cars only and under ideal conditions. Design or practical capacities under ideal traffic and roadway conditions are as follows:

  22. The preceding capacity values gives as practical capacities pre-assume the following: • - Traffic lane width is 3.65 m.(12 ft.); • -Side clearance from pavement edge to vertical obstructions  1.85 m.(6 ft.); • -Shoulders are wide enough for parking vehicles to clear the pavement; • - Traffic consists of passenger cars only; • - Alignment and grade are not restrictive.

  23. 1-Effect of lane width: A lane width of 12 ft. is assumed necessary for ideal conditions. Any reduction in lane width will decrease the capacity. 2.Effect of lateral clearance: A lateral clearance of 6.0 ft. from pavement edge to vertical obstruction is essential for ideal conditions. Reduction in this value will decrease the capacity. The combination effect of two last factors is given in Tab.5

  24. 3.Efect of commercial vehicles: One commercial vehicle has the effect of two passenger cars on level roads, 4 PC in rolling terrain , and about 8 PC in mountainous country. Effect of commercial vehicles on practical capacity is shown in Tab.6. The passenger car equivalent for different vehicles on flat surface are as follows: Cycles = 0.5 PC Motor cycle =1.0 PC Pedestrians = 0.1 PC Animal driven veh. =6.0 PC Buses =2.0 PC Hand -driven carrots =2.0 PC Street cars (Trams) = 4.0 PC

  25. 4.Effect of imperfect alignment: Imperfect alignment and breaks in the profile reduce the distance that a driver can see a head along the road. If this distance is less than 1500 ft. on a 2-lane road, the road capacity will be reduced because it will not be safe to make many passing maneuvers (see Tab.7). 5.Effect of grades: Speeds of trucks are markedly affected when the grades are up 6 or 7%, while passenger cars are little influenced. Road capacity decreased only when the speeds fall below 30 mph.

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