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ch. 5 traffic Island.pptx

  1. Prof. Mehul M Chavda Design Geometric Design intersection & Traffic Island
  2. Introduction 1. Intersection at grades 2. Grade separated intersections 3. Traffic island 4. Terminal facilities
  3. Intersections • Intersection is the location on a roadway where two or more approaches from different directions are meeting. 1. Intersection at Grade 2. Grade separated Intersection
  4. INTERSECTION AT GRADE • Unchannelized Intersection • Channelized Intersection • Rotary Intersection
  5. Classification of Intersection at Grade A) According to Shape:- Three legged intersection (T, Y and skewed) Four legged intersection (Right angled, skewed, offset) Rotary intersection B) According to Geometric design features:- Unchannalized intersection Channelized intersection C) According to traffic control:- Uncontrolled intersection Controlled Intersection Signalized intersection D) According to levels of crossing:- At grade intersections Grade separated intersections
  6. Requirements of intersection at Grade • At the intersection the area of conflict should be as small as possible. • For the vehicles, adequate visibility should be available. • The relative speed and angle of approach of vehicles should be small. • Sudden change of path should be avoided. • Proper signs should be provided. • Proper lighting should be provided for better visibility at night.
  7. Unchannelized Intersections • The intersection area is paved and there is absolutely no restriction to vehicle to use any part of intersection area. • Lowest class of intersection • Easy to design but most complex in traffic operations resulting in maximum conflict area and more no of accidents.
  8. Channelized Intersections • Channelized Intersections is achieved by introducing islands into the intersectional area, thus reducing total conflict area available. • These are help to channelize turning traffic, to control their speed and to decrease conflict area.
  9. Advantages of Channelized Intersections • By channelization, vehicles confined to definite path. • Conflict areas can be decreased. • Angle of merging streams can be forced to be flat angles so as to cause minimum disruption. • Speed of vehicle can be controlled. • Refuse islands can be provided for pedestrians. • Points of conflicts can be separated. • Signs & traffic devices can be installed.
  10. TRAFFIC ISLANDS • Traffic islands are raised areas constructed within the roadway to establish physical channels through which the vehicular traffic may be guided.
  11. FUNCTIONS OF TRAFFIC ISLANDS • Functions of Traffic Islands:- • To segregate the pedestrians and vehicles. • To separate traffic into specified paths. • To reduce conflict areas. • To increase safety • To divert traffic from obstacles.
  12. ADVANTAGES OF TRAFFIC ISLANDS • It provides smooth and controlled traffic flow. • It reduces the accident and increase safety • It gives uniform speed of traffic. • No need of police control.
  13. DISADVANTAGES OF TRAFFIC ISLANDS • It consumes useful traffic area. • It increases travel distance. • Width of traffic lane decreases.
  14. TYPES OF TRAFFIC ISLANDS 1. Divisional islands 2. Channelizing islands 3. Pedestrian loading islands 4. Rotary islands
  15. Conflicts at an Intersection  Crossing conflicts  Merging conflicts  Diverging conflicts
  16. VISIBILITY AT INTERSECTIONS  At intersection where the intersecting roads are of more or less equal importance & there is no established priority, visibility should be provided .  SSD is given by,  SSD = lag distance + breaking distance
  17. SSD values for different speeds DESIGN SPEED ( SAFE SSD (m) 20 20 25 25 30 30 40 45 50 60 60 80 65 90 80 120 100 180
  18.  It is customary to control traffic on the minor road by STOP or GIVEWAYsign or road markings.  Such intersection are known as Priority Intersection.  Priority to the right is a right-of-way system, in which the driver of a vehicle is required to give way to vehicles approaching from the right at intersections.
  19. WIDTH OF CARRIAGEWAY  Width needs to be increased in curves, keeping in mind mechanical widening and psychological widening.  Extra Widening = Mechanical Widening + Psychological Widening  We = nl ²/2R + V/9.5(R)½
  20. MEDIAN OPENINGS  At Intersections, where nearly all the traffic travels on the divided highway and volume is below capacity, the occasional vehicles may use the median opening either to come to the through road from the cross road or reverse.  A bullet nosed median opening designed for the minimum turning path will meet the requirements.  A bullet nosed median end is preferable.  The length of opening depends on the width of median.
  21. Median opening with bullet nosed end
  22. T-INTERSECTION  It is normally provided for very light traffic and for minor and local roads.  For locations where speeds are high and turning movements are large, it is hazardous.
  24. Y-INTERSECTION  Mostly design features are similar to that of T- Intersections, except where the intersection angle is very acute.
  26. CROSS ROADS  In case of cross roads, two roads crosses approximately at right angles.  Uncontrolled cross roads are very dangerous due to high accident rate.
  28. STAGGERED INTERSECTION  The safety at the cross roads can be significantly enhanced by converting it into a staggered intersection.  A minimum distance of 35 m is necessary between the staggered roads.  A right/left staggered is preferred to left/right stagger where there are no separate right turning lanes.
  31. ROTARY INTERSECTION  A ROTARY INTERSECTION is an enlarged road intersection where all converging vehicles are forced to move round a large central island in one direction before they can weave out of traffic flow into their respective directions radiating from the central island.  The main object of providing a rotary are to eliminate the necessity of stopping even for crossing streams of vehicles and to reduce area of conflict.
  32. Advantages of rotary intersection • It ensure one way traffic movement • Frequent starting and stopping are avoided • Vehicles move at uniform speed • It reduces crossing conflicts from 16 to4 • No need of traffic police or signal • Maintenance is negligible • Easy movement of right turn traffic
  33. Disadvantages of rotary intersection • It require large area • It does not provide any provision for pedestrian • Difficult to separate slow traffic movement • It require may warning and direction sign for safety
  34. ROTARY DESIGN ELEMENTS Design Speed Shape of central island Radius of entry Radius at exit Radius of central island Weaving length Width of carriage way at entry and exit Width of rotary carriageway Entry and exit angles Camber and super elevation Capacity
  35. GRADE SEPARATED INTERSECTIONS  In a grade separated intersection, the intersecting roadways are placed at different elevations to allow uninterrupted traffic movement.  The grade separated intersections are classified as OVERPASS and UNDERPASS.  When the major highway is taken over the road of lesser importance, it is called as OVERPASS.  If the major highway is taken by depressing it below the ground level to cross another road of less importance by means of under bridge, it is known as UNDERPASS.
  40. ADVANTAGES OF GRADE SEPARATION It avoids necessity of stopping. Avoids accidents at intersection. There is increased safety or turning traffic. There is overall increase in comfort and convenience to the motorists and saving in travel time. It is very useful for expressways.
  41. DISADVANTAGES OF GRADE SEPARATION It is very costly. Where there is limited right of way like built up or urban area or where topography is not favourable, construction of grade separation is costly, difficult and undesirable.
  42. TYPES OF GRADE SEPARATED INTERSECTION  Grade separated intersections without interchange.  Grade separated intersections with interchange.  Depending upon no of legs the intersection serves, they are classified as-  A) Three-legged Interchange  T-Intersection  Y-Intersection  Partial rotary interchange B) Four legged interchange  Diamond Interchange  Clover leaf interchange  Rotary Interchange  Directional Interchange C) Multi-legged interchange  Rotary interchange
  45. TERMINAL FACILITIES  Along the highway the terminal facilities required are:- Bus stops Bus bays Drive ways Footways
  46. • Thank You