![SSD contd..
• Minimum stopping sight distance is the sum of
(i)distance travelled during the perception and brake
reaction time [Lag Distance]
(ii) the braking distance
• Lag distance = v.t
v = design speed in m/s
t = total reaction time of the driver – IRC
recommends t = 2.5 s for SSD calculations](https://image.slidesharecdn.com/hagdpptcep-240322162448-b80e1f30/85/highway-enginering-geometric-design-ppt-72-320.jpg)
highway enginering geometric design .ppt
- 2. Outline 1: Introduction - Road User Characteristics 2: Classification of Roads 3: Highway Geometric Design 4: HorizontalAlignment 5: V erticalAlignment 6: Coordination of alignments 2
- 3. 1.INTRODUCTION • Indian road network of 6.3 million Km is the second largest in the world and consists of : CLASSIFICATION OF ROADS NON-URBAN ROADS URBAN ROADS CLASSIFICATION LENGTH(in Km) Expressways 5,342 National Highways 1,51,000 State Highways 1,86,528 Major District Roads 6,32,154 Rural and Other Roads 45,35,511 3
- 5. 5 Human element • PHYSICAL • MENTAL • PSYCHOLOGICAL • ENVIRONMENTAL
- 6. 6 PHYSICAL CHARACTERISTICS…. • VISION • HEARING • STRENGTH & • GENERAL REACTION TO TRAFFIC SITUATIONS
- 7. VISION The human eye is the sensory organ that enables one to see and evaluate the size, shape and colour of the objects and estimate distances and speeds of bodies. 7
- 8. 8 ACUITY OF VISION • Field of acute clear & acute vision is within a cone whose angle is only 3 degrees • Up to 10 degree satisfactory in general • Even up to 20 degree in the horizontal plane • This is important when locating traffic signs and signals
- 9. Acuity of vision 9
- 10. Vision cone 10
- 11. 11 3.1.2 PERIPHERAL VISION • Deals with the total visual field for the two eyes • The angle of peripheral vision is about 160 degree in the horizontal direction & 115 degree in the vertical direction • The angle of cone falls down 110 degree( @ 30 kmph) 40 degree (@100 kmph)
- 12. 12
- 13. CONTINUES…. • COLOUR VISION •DRIVERS ABILITY TO ADAPT TO THE GLARE (GLARE RECOVERY TIME 3-6 SECONDS) • THE ABILTY TO JUDGE THE DEPTH DISTANCE & SPEED OF AN OBJECT 13
- 14. HEARING • SOUND OF HORN ALERT PEDESTRIAN • ELDERLY PERSONS WITH FALLING EYESIGHT CAN PERCEIVE BETTER THROUGH HEARING • DEFECTIVE HEARING- NOT A SERIOUS HANDICAP 14
- 15. 15 STRENGTH – Difficulties in rapid decision making • At intersections – Take time to absorb traffic control information – Difficulty at night • Lower light level • Headlight glare – Readily fatigued
- 16. 16 MENTAL CHARACTERISTICS • KNOWLEDGE OF VEHICLE CHARACTERISTICS, TRAFFIC BEHAVIOUR, DRIVING PATIENCE, RULE OF ROADS, PSHYCHOLOGY OF OTHER DRIVERS…. • SKILL • INTELLIGENCE • EXPERIENCE- REACTIONS BECOME SPONTANEOUS • LITERACY- TRAFFIC REGULATIONS & SPECIAL INSTRUCTIONS • PATIENCE
- 17. PSYCHOLOGICAL • PERCEPTION • INTELLECTION • EMOTION • VOLITION 17
- 18. PSYCHOLOGICAL 18
- 19. 19 ENVIRONMENTAL • TRAFFIC STREAM CHARACTERISTICS -MIXED OR HOMOGENIC -HEAVY OR LIGHT • TRAFFIC FACILITY • ATMOSPHERIC CONDITIONS - CLOUDY - DUSTY • LOCALITY
- 20. DESIGN VEHICLE Selected motor vehicles with weight, dimensions, and operating characteristics used to establish highway design controls Design vehicle has larger physical dimensions and a larger minimum turning radius than most vehicles in its class.
- 21. Influence on the geometric design aspects of roads • Radii • width of pavements • clearances • parking geometrics etc.
- 22. Design aspects of an intersection • horizontal and vertical alignments • lane widths • turning radii • intersection sight distance, • storage length of auxiliary lanes • acceleration and deceleration lengths on auxiliary lanes.
- 23. TYPES OF DESIGN VEHICLES • Four general classes of vehicles have been established. • passenger cars • Buses • Trucks • recreational vehicles • The passenger car class includes compacts, subcompacts, sedans, pick-up trucks, SUVs, minivans, and full-size vans. • Buses include inter-city (motor coaches), city transit, school, and articulated buses.
- 24. DIMENSIONS OF DESIGN VEHICLE Standardization of the dimensions and weights of vehicles is done by • AASHTO – American Association of State Highway and Transportation Officials • IRC – India Road Congress • Ministry of transport regulations - UK
- 25. Authority/ country Maximum width Maximum Height Maximum Overall Length Passeng er car Single unit truck Semi trailer Truck trailer Single unit bus UK 2.5 4.57 5.5 11 13 18 - IRC 2.5 3.8 - 4.2(Truck) 4.75 (Double decker bus) - 11 16 18 12
- 26. • Maximum axle loads in Tonnes Single axle Tandem Axle U.K 10 - IRC 10.2 18
- 27. 27 IRC CLASSIFICATION • CLASSIFICATION OF NON-URBAN ROADS : 1. National Highways(NH) 2. State Highways(SH) 3. Major District Roads(MDR) 4. Other District Roads(ODR) 5. Village Roads(VR)
- 28. 28 NATIONAL HIGHWAYS • Important roads of the country. • Connect state capitals, ports, foreign highways. • Include roads of military importance. • Financed by the central government.
- 29. 29 STATE HIGHWAYS • Important roads of a state. • Connect: – important cities and district head quarters in the state, – national highways & state highways of neighbouring states. • Construction, maintainance & funding – by state government • NH and SH have same design speed and geometric design.
- 30. 30 MAJOR DISTRICT ROADS • These are the roads within a district . • Serves areas of production and markets. • Connecting these with each other or with main highways. • Financed by zillaparishads with the help of grants given by state government.
- 31. 31 RURAL ROADS 1. OTHER DISTRICT ROADS • Roads serving rural areas of production. • Provides outlet to market centres, taluk headquarters and to other main roads. 2. VILLAGE ROADS • Connects villages or group of villages with each other • And to the nearest road of a higher category
- 32. 32
- 33. 33
- 34. Expressway contd… • Eg. Golden quadrilateral • Largest express highway project in india • One of the longest highways in the world 34
- 35. 35
- 36. 36
- 37. HIERARCHY 37
- 38. 38
- 39. 39
- 40. 40
- 41. 41 2. Highway Geometric Design • TERRAIN AND ITS DESCRIPTION • An area of land, when considering its natural features. • A knowledge of terrain, that is the land as a working surface is required for planning highway operations. • Terrain classification has been described by means of text descriptions ,by reference to ground contours, and in terms of cross-slope.
- 42. CLASSIFICATION • Terrain is classified based on the percentage of cross slope that is slope approximately in the perpendicular direction of the road that’s what is normally indicated as cross slope TERRAIN CLASSIFICATION % CROSS SLOPE PLAIN ROLLING MOUNATAINOUS STEEP UPTO 10 10 TO 25 25 TO 60 >60
- 43. TERRAIN CLASSIFICATION AS PER ROAD USER COST STUDY • An extensive survey of 42,000 km of roads in India as part of the Road User Cost Study has enabled the development of system of Terrain classification (Source L.R.kadiyali)
- 44. QUANTIFICATION OF CURVATURE : PLAN Average Curvature of section AB= ф1+ф2+ф3+---------- фn/Distance(AB) (Source L.R.kadiyali)
- 45. QUANTIFICATION OF RISE AND FALL: LONGITUDINAL PROFILE Average Rise of section AB= h1+h3+---------- hm/Distance AB (KM) Average Fall of section AB= h2+h4+---------- hn/Distance AB (KM) (Source L.R.kadiyali)
- 46. GRADIENTS FOR ROADS IN DIFFERENT TERRAIN S TERRAIN RULING GRADIENT LIMITING GRADIENT EXCEPTIONAL GRADIENT PLAIN & ROLLING MOUNATAINOUS STEEP 3.3% 5% 6% 5% 6% 7% 6% 7% 8% (Source IRC: 73-1980.)
- 47. 47 DESIGN SPEED • Depends on class of road and terrain • Ruling Speeds – Guiding criteria for geometric design • Min Speed – used where site conditions or economic considerations warrant
- 48. DESIGN SPEEDS IRC 73-1980 48
- 49. 49 Cross Sectional Elements-introduction • Features that deals with the width of highway • Influences life of pavement, riding comfort and safety • Different cross sectional elements are Carriageway Shoulders Roadway width Right of way Building line and control line Central reservations(Median) Camber Side slope Lateral and vertical clearances Curbs (Kerbs)
- 50. Building Line and Control line • Control construction/developmental activities 50
- 51. 51 Carriageway • Paved surface used for vehicular movements • Takes vehicular loading • Cement concrete, bituminous pavement etc. • Width depends on no. of lanes- single lane, two lane or multi lane • Intermediate lane width is provided for essential manoeuvres like overtaking or crossing WIDTH OF CARRIAGEWAY(meters) SINGLE LANE INTERMEDI ATE LANE TWO LANES WITHOUT RAISED KERBS TWO LANES WITH RAISED KERBS MULTI LANE ROAD(WIDTH PER LANE) 3.75 5.5 7 7.5 3.5
- 52. How width is decided?? http://www.cdeep.iitb.ac.in/ 52
- 53. Shoulder • Basically gives support to carriageway • Provides space for stopped vehicles(parking) • One half the distance between roadway width and carriageway width 53
- 54. 54 Roadway • Carriageway(including separators) and shoulders together constitute the roadway • Roadway width also known as width of formation • Roadway width depends on the type of terrain • Different for different type of roads ROAD CLASSIFICATI ON ROADWAY WIDTH IN m PLAIN AND ROLLING TERRAIN MOUNTAINEO US AND STEEP TERRAIN NH/SH 12 6.25-8.8 MDR 9 4.75 ODR 7.5-9.0 4.75 VR 7.5 4
- 55. 55 • Culverts (upto 6m span)- normal roadway width is to be provided measured from outside to outside of the parapet walls • Bridges(greater than 6m span) –clear width of roadway between kerbs should be as under • Single lane bridge -4.25 m • Two lane bridge -7.5m • Multilane bridge carriageway --3.5 m per lane + 0.5 m for each • At causeways and submersible bridges -7.5m
- 56. Right of way (ROW) • Right of way or land width • Land secured and preserved for road purpose • Should be adequate to accommodate all the cross section elements • Should provide space for future upgradation • the type of Depends on type of terrain and area(open or built up) 56
- 57. IRC 73-1980 specifications RIGHT OF WAY WIDTH IN meters plain and rolling terrain mountaineous and steep terrain CLASS OF ROAD rural areas urban areas rural areas urban areas Normal Range Normal Range Normal Exceptiona l Normal Exception al NH/SH 45 30-60 30 30-60 24 18 20 18 MDR 25 25-30 20 15-25 18 15 15 12 ODR 15 15-25 15 15-20 15 12 12 9 VR 12 12--18 10 15-20 9 9 9 579
- 58. PLAIN AND ROLLING TERRAIN MOUNTAINEOUS AND STEEP TERRAINS OPEN AREAS BUILT UP AREAS OPEN AREAS BUILT UP AREAS ROAD CLASSIFICATI ON OVERAL L WIDTH BETWE EN BUILDI NG LINES(metres) DISTANCE BETWEEN ROAD BOUNDARY BUILDING LINE(SETBACK) metres OVERALL WIDTH BETWEEN CONTROL LINES(metres) DISTANCE BETWEEN ROAD BOUNDARY BUILDING LINE(SETBACK) metres NH/SH 80 150 3--6 3--5 3--5 MDR 50 100 3--5 3--5 3--5 ODR 25/30 35 3--5 3--5 3--5 VR 25 30 3--5 3--5 3--5 REF: IRC 73-1980
- 59. MEDIANS • Longitudinal space separating dual carriageways • Separates directional traffic streams • Should be as wide as possible • Width is restricted by economic consideration • Uniform width is preferable • Width depends on the type of road/cross drainage structure and availability of land • Transition length for change in width • Right turning pockets • Reduce head light glare 59
- 60. 60 • Minimum desirable width on rural highways -5 m (reduced to 3m if land is restricted) • On bridges and viaducts-1.5m • Should not be less than 1.2m • Desired transition in width- 1 in 15 to 1 in 20 (IRC 73-1980 specifications)
- 61. Camber • To drain off rain water from road surface • Depends on type of road and amount of rainfall SURFACETYPE CAMBER/CROSSFALL HIGH TYPE BITUMINOUS SURFACING OR CEMENT CONCRETE 1.7-2.0 % THIN BITUMINOUS SURFACING 2.0-2.5% WATER BOUND MECADEM, GRAVEL 2.5-3.0% EARTH 3.0-4.0% IRC 73-1980 61
- 62. • Shapes of camber • Parabolic • Straight line • Or combination http://www.cdeep.iitb.ac.in/ 62
- 63. 63 Kerbs (curbs) • Vertical or sloping member along the edge of pavement or paved shoulder • Desirable for urban roads • Facilitates and controls drainage • Strengthens and protects pavement edge • Delineates pavement edge • Presents more finished appearance • Encourages orderly roadside development
- 64. • Types of kerbs • Mountable • Semi barrier type • Barrier type 64
- 65. Sight Distances • Visibility is an important requirement for the safe travel on highways. • Driver from a specified height above carriageway should have visibility of stationary and moving objects. • SIGHT DISTANCE is the length of road visible ahead to the driver at any instance.
- 66. • Restrictions to sight distances may be caused at horizontal, vertical curves and at intersections.
- 69. • Three types of sight distances are relevant insofar as the design of summit vertical curves and visibility at horizontal curves: • 1) Stopping Sight Distance • 2) Overtaking Sight Distance • 3) Intermediate Sight Distance • For valley curves design is governed by night visibility which is reckoned in terms of the Headlight Sight Distance.
- 70. Stopping sight distance • Stopping Sight Distance (SSD) is the clear distance ahead needed by a driver to bring his vehicle to a halt before meeting any other obstruction in his path. • Sight distance available on a road to a driver at any instance depends on : • 1) Features of the road ahead – horizontal alignment, vertical profile, traffic condition, position of obstruction • 2) Height of the driver’s eye above the road surface – IRC suggests height of eye level of driver as 1.2 m
- 71. • 3) Height of the object above the road surface – IRC suggests height of the object as 0.15 m above the road surface. • SSD further depends on a) Total reaction time of driver b) Speed of vehicle c) Efficiency of brakes d) Frictional resistance between road and tyres e) Gradient of the road
- 72. SSD contd.. • Minimum stopping sight distance is the sum of (i)distance travelled during the perception and brake reaction time [Lag Distance] (ii) the braking distance • Lag distance = v.t v = design speed in m/s t = total reaction time of the driver – IRC recommends t = 2.5 s for SSD calculations
- 73. SSD contd.. Braking distance • For a level road this is obtained by equating the work done in stopping the vehicle and the kinetic energy of the vehicle • If F is the maximum frictional force developed and the braking distance is l, then work done against friction in stopping the vehicle is Fl = fwl fwl = 1 mv² 2 𝑣2 l = 2𝑔 𝑓
- 74. v = design speed in m/s g = acceleration due to gravity f = design coefficient of friction • SSD = 𝑣𝑡 + 𝑣² 2𝑔 𝑓 • SSD at slopes = 𝑣𝑡+ 𝑣² 2𝑔(𝑓±0.01𝑛) • +n is ascending gradient and –n is descending gradient
- 75. Overtaking sight distance (OSD) • The overtaking sight distance is the minimum distance open to the vision of the driver of a vehicle intending to overtake the slow vehicle ahead safely against the traffic in the opposite direction • The overtaking sight distance or passing sight distance is measured along the centre line of the road over which a driver with his eye level 1.2 m above the road surface can see the top of an object 1.2 m above the road surface.
- 77. The factors that affect the OSD are: • Velocities of the overtaking vehicle, overtaken vehicle and of the vehicle coming in the opposite direction. • Spacing between vehicles, which in-turn depends on the speed • Skill and reaction time of the driver • Rate of acceleration of overtaking vehicle • Gradient of the road
- 78. The overtaking sight distance consists of three parts: • d1 = The distance travelled by overtaking vehicleAduring the reaction time t = t1 – t0 • d2 = The distance travelled by the vehicle during the actual overtaking operation T = t3 – t1 • d3 = Is the distance travelled by on-coming vehicle C during the overtaking operation • OSD = d1+d2+d3
- 79. • It is assumed that the vehicleAis forced to reduce its speed to vb the speed of the slow moving vehicle B and travels behind it during the reaction time t of the driver Therefore, d1 = vb.t • Then the vehicle A starts to accelerate with acceleration a, shifts the lane, overtake and shift back to the original lane. The vehicleAmaintains the spacing s before and after overtaking. s is given by empirical formula 𝑠 = 0.7𝑣𝑏 + 6 in metres
- 80. • Let T be the duration of actual overtaking. The distance travelled by B during the overtaking operation is 2𝑠 + 𝑣𝑏𝑇. Also, during this time, vehicleAaccelerated and overtaking is completed. 1 𝑑2 = 𝑣𝑏𝑇 + 2 𝑎𝑇2 1 𝑣𝑏𝑇 + 2𝑠 = 𝑣𝑏𝑇 + 2 𝑎𝑇2 𝑇 = 4𝑠 𝑎
- 81. • The distance travelled by the vehicle C moving at design speed v during overtaking operation is given by 𝑑3 = 𝑣𝑇 • IRC recommends vb = v – 4.5 • d3 is not required when there is no opposing traffic. • Overtaking zones are provided when OSD cannot be provided throughout the length of the highway. These are zones dedicated for overtaking operation, marked with wide roads. The desirable length of overtaking zones is 5 time OSD and the minimum is 3 times OSD .
- 83. Intermediate sight distance • Adistance equivalent to twice the stopping sight distance, a distance where overtaking could be attempted with reasonable safety. • Overtaking is mostly prohibited at horizontal curves using regulatory signs. • In case of vertical summit curves, it is possible to provide ISD • ISD = 2 SSD • Measurement of ISD is made on assuming both the height of driver’s eye level and height of object are 1.2m from road surface.
- 84. Headlight Sight distance • This is the distance ahead of the vehicle illuminated by the headlights which is within the view of the driver. • The design must ensure that the roadway ahead is illuminated by vehicle headlights to a sufficient length enabling the vehicle to brake to a stop if necessary. • The following criteria to be maintained: a) height of headlight above the road surface is 0.75m b) The useful beam of headlight is upto 1° upwards from the grade of road c) the height of the object is nil • HSD = SSD
- 85. HSD contd..
- 86. SIGHT distances at intersection • At intersections where two or more roads meet, visibility should be provided for the drivers approaching the intersection from either sides. • They should be able to perceive a hazard and stop the vehicle if required. • Stopping sight distance for each road can be computed from the design speed. • The sight distance should be provided such that the drivers on either side should be able to see each other.
- 87. • Design of sight distance at intersections may be used on three possible conditions: a) enabling approaching vehicle to change the speed b)enabling approaching vehicle to stop c)enabling stopped vehicle to cross a main road
- 89. 89 HORIZONTAL ALIGNMENT • The position or the layout of the central line of the highway on the ground is called the alignment. • Horizontal alignment includes straight and curved paths. • Consistent, safe, smooth movement of vehicles • Design Factors – Design Speed – Radius of Circular Curve – Superelevation – Extra widening – Type and length of transition curves
- 90. 90 DESIGN SPEED • Depends on class of road and terrain • Ruling Speeds – Guiding criteria for geometric design • Min Speed – used where site conditions or economic considerations warrant
- 91. DESIGN SPEEDS IRC 73-1980 91
- 93. HORIZONTAL CURVES • Curve in plan to provide change in direction • Centrifugal force acting outwards 93
- 95. 95 DEFINITION • The outer edge of road at the horizontal curve is raised above the inner edge. This is super elevation. • Given throughout the length of horizontal curve to reduce the effect of centrifugal force on the running wheels. • It is also sometimes termed as banking.
- 97. ANALYSIS OF SUPERELEVATION 97 Source:Khanna & Justo
- 98. ANALYSIS OF SUPERELEVATION Source:Khanna & Justo 98
- 99. • Resolving the forces parallel and perpendicular to the inclined road surface, PcosӨ = WsinӨ + FA + FB • 99
- 100. • Equilibrium superelevation : when f = 0, high rate of SE 100
- 101. 101 SUPERELEVATION DESIGN • For fast moving vehicles, neglecting lateral friction is safer • For slow moving vehicles, high rate of SE is inconvenient. • As a compromise, – SE is provided to counteract centrifugal force due to 75% design speed. – Limit the max superelevation
- 102. 102 MAX SUPERELEVATION • Plain and rolling terrain – 7% • Hilly roads not bounded by snow – 10%
- 103. STEPS FOR SUPERELEVATION DESIGN i. ii. If e <emax , provide the value obtained. Else e = emax and check for f as per step iii. iii. Check for f . If f<0.15, emax is safe iv. If f>0.15, restrict the speed in curve or increase the radius of the curve after providing emax 103
- 104. If required SE cannot be provided, • Restrict the velocity • Increase the radius R= 104
- 105. 105 MIN SUPERELEVATION • For drainage considerations, a minimum cross slope is required. • Min SE = camber
- 106. 106 METHOD OF ATTAINMENT Two stages I. Outer half of camber is gradually raised until its level and subsequently rotated to obtain uniform cross slope II. Rotation of pavement to attain full superelevation
- 107. STAGE I-ATTAINING SUPERELEVATION EQUAL TO CAMBER 107 Outer half of camber is raised gradually & brought to level at the start of the transition curve Source: Khanna & Justo
- 108. STAGE I (Contd..) 108 Subsequently the outer half is further rotated to obtain uniform cross slope equal to camber Source: Khanna & Justo
- 109. STAGE II-ATTAINING FULL SUPERELEVATION 3 Methods • Rotation about centerline • Rotation about inner edge • Rotation about outer edge 109
- 110. STAGE II (Contd..) i. About the center line • Gradually lowering the inner edge and raising the upper edge .Level of centerline constant 110 Source:L.R Kadiyali
- 111. STAGE II (Contd..) ii. About the inner edge • Raising centre and outer edge 111 Source:L.R Kadiyali
- 112. STAGE II (Contd..) iii. About the outer edge • Depressing the center and inner edge 112 Source:L.R Kadiyali
- 113. • SE is gradually attained over full length of transition curve so that desired SE is available at starting of circular curve • Rate of introduction of SE – Plain and Rolling Terrain – 1 in 150 – Mountainous and steep terrain – 1 in 60 113
- 115. RADIUS OF HORIZONTAL CURVE • Centrifugal force is dependent on radius of the horizontal curve. • To keep centrifugal ratio within a low limit , the radius of the curve should be kept correspondingly high. • If the design speed is decided for a highway, then the minimum radius to be adopted can be found from the following relationship, i.e., e+f =v2/gR
- 116. Ruling Minimum Radius: Rruling = 𝑣2 𝑒 : 𝑓 𝑔 , where v is ruling design speed in m/sec. Absolute Minimum Radius: min R = 𝑣12 𝑒 : 𝑓 𝑔 , where v1 is minimum design speed in m/sec. Minimum radius of the curve is obtained by adopting maximum values for both e and f
- 117. Table showing Design Speeds on Rural Highways for different terrain conditions
- 118. Table showing minimum radii of horizontal curves for different terrain conditions classification PLAINTERRRAIN ROLLING TERRAIN MOUNTAINOUS TERRAIN STEEPTERRAIN AREAS AFFECTED BY SNOW SNOW BOUND AREAS AREAS AFFECTED BY SNOW SNOW BOUND AREAS Road RULING MIN RADIUS ABSOLU TE MIN RADIUS RULING MIN RADIUS ABSOLU TE MIN RADIUS RULING MIN RADIUS ABSOLU TE MIN RADIUS RULING MIN RADIUS ABSOLU TE MIN RADIUS RULING MIN RADIUS ABSOLU TE MIN RADIUS RULING MIN RADIUS ABSOLUT E MIN RADIUS NH & SH 360 230 230 155 80 50 90 60 50 30 60 33 MDR 230 155 155 90 50 30 60 33 30 14 33 15 ODR 155 90 90 60 30 20 33 23 20 14 23 15 VILLAGE ROADS 90 60 60 45 20 14 23 15 20 14 23 15 Source-IRC:73-1980
- 119. WIDENING OF PAVEMENT ON HORIZONTAL CURVE It includes • Need for extra widening • Analysis of extra widening on curves • Methods of introducing extra widening
- 120. Need for extra widening: Fig(i) Fig(ii)
- 121. • Widening of the pavement on the horizontal curves is governed by the following factors: (a) Length of the wheel base (b) Radius of the curve negotiated, R (c)Psychological factor which depends upon the velocity of the vehicle and the radius of the curve
- 122. Analysis of extra widening on curves: It is divided into: a)Mechanical widening b)Psychological widening
- 123. a)Mechanical widening(Wm) • Widening required to account for the off-tracking due to rigidity of wheel base DERIVATION: Let R1 be the radius of the path traversed by the outer rear wheel , m R2 be the radius of the path traversed by the outer front wheel , m wm be the off-tracking or the mechanical widening , m l be the length of wheel base , m From fig , wm = R2 – R1 eq (i) R1 = R2 - wm -------------- & R1 2 = R2 2 – l2 ------------ eq (ii) Substitute eq(i) in eq(ii) On further simplification of eq (ii) we arrive at wm = l2 /(2R2 – wm ) m 𝑙2 2𝑅 / therefore , w = , where R is the mean radius of the curve for a road having ‘n’ traffic lanes , mechanical widening required is wm 𝑛𝑙2 = 2𝑅
- 124. b)Psychological widening(wps ) • for providing greater maneuverability of steering at higher speeds • provide greater clearance for crossing and overtaking vehicles on the curves IRC provides an empirical relation for the psychological widening at the horizontal curves ps w = 𝑉𝑘 9.5 𝑅 , v in kmph Therefore, the total extra widening to be provided is e W = 𝑛 𝑙 2 + 𝑉𝑘 2𝑅 9.5 𝑅
- 125. The extra widening recommended by the IRC for single lane and two lane pavements For multi-lane roads, the pavement widening is calculated by adding half of the extra width of two-lane road to each lane of the multi-lane road Radius of curve (m) up to 20 20 to 40 41 to 60 61 to 100 101 to 300 above 300 Extra Width (m) Two-lane 1.5 1.5 1.2 0.9 0.6 Nil Single-lane 0.9 0.6 0.6 Nil Nil Nil
- 126. Methods of introducing extra widening
- 127. 127 Transition Curve • Transition curve ensures a smooth change from straight road to circular curves. • Transition curve is provided to change the horizontal alignment from straight to circular curve gradually and has a radius which decreases from infinity at the straight end (tangent point) to the desired radius of the circular curve at the other end (curve point).
- 128. 128
- 129. 129 Need and Objective • The objectives for providing transition curves are: 1. to introduce gradually the centrifugal force between the tangent point and the beginning of the circular curve, avoiding sudden jerk on the vehicle. This increases the comfort of passengers. 2. to enable the driver turn the steering gradually for his own comfort and security, 3. to provide gradual introduction of super elevation, and 4. to provide gradual introduction of extra widening. 5. to enhance the aesthetic appearance of the road.
- 130. 130 Types of Transition Curve • Different types of Transition curves are: spiral or clothoid, cubic parabola, and Lemniscate. • IRC recommends spiral as the transition curve because it fulfills the requirement of a ideal transition curve 1) rate of change of centrifugal acceleration is consistent (smooth) 2) radius of the transition curve is ∞ at the straight edge and changes to Rat the curve point 3) calculation and field implementation is very easy.
- 131. 131 Length of Transition Curve: • The length of the transition curve should be determined as the maximum of the following three criteria: 1) Rate of change of centrifugal acceleration 2) rate of change of super elevation and 3) an empirical formula given by IRC
- 132. Length of Transition Curve: 1) Rate of change of centrifugal acceleration: If Cis the rate of change of centrifugal acceleration 132
- 133. Length of Transition Curve: 133
- 134. Length of Transition Curves: 134
- 135. Length of Transition Curve: 135
- 136. Length of Transition Curve: 136
- 138. Set Back Distance • Adequate sight distance on horizontal curves: an essential consideration • Absolute minimum sight distance- safe stopping sight distance should be available at every section of the highway • Horizontal curve- location with problems of sight distance • Need of adequate sight distance- safe and efficient movement of traffic
- 139. • Obstruction to sight distance: buildings, trees, cut slopes etc. along the inner side of the horizontal curves • Set- back distance: to provide adequate sight distance on horizontal curves
- 140. Set-back distance is basically the clear distance in the inner side of the curve which must be available to make sure that adequate sight distance is available on horizontal curve.
- 141. Set- back distance depends on : • required sight distance(S) • radius of horizontal curve(R) • length of curve(L)
- 142. Sight distance • Required sight distance could be - stopping sight distance - intermediate sight distance - overtaking sight distance • On narrow roads, the sight distance is measured along the central line of the road- single lane road • On wider roads, the sight distance is measured along the central line of the inner side lane of the road - critical vehicle position • Overtaking sight distance or passing sight distance – more set- back distance
- 143. Radius of horizontal curve • Sharper curves- more set back distance LENGTH OF HORIZONTAL CURVE Two cases Length of the horizontal curve more or less than the required sight distance
- 144. Set back distance, m = R-(R-d)cos(α/2)
- 145. SETTING OUT OF HORIZONTAL ALIGNMENT 145
- 146. • The horizontal alignment consists of straight sections of the roads, known as tangents, connected by horizontal curves. • The curves usually segments of circles. • Horizontal curves are usually used to change the alignment direction Introduction 146
- 147. Circular Curve with Transition Curve 147
- 148. • The vertical alignment should provide for a smooth longitudinal profile consistent with category of the road and lay of the terrain. • Grade changes should not be too frequent as to cause kinks and visual discontinuities in the profile. • There should be no change in grade within a distance of 150m. VERTICAL ALIGNMENT
- 149. S.NO. Terrain Ruling gradient Limiting gradient Exceptional gradient 1 Plain and rolling 3.3 per cent (1 in 30) 5 per cent (1 in 20) 6.7 per cent (1 in 15) 2 Mountainous terrain and steep terrain having more than 3000m above the mean sea level 5 per cent (1in 20) 6 per cent (1 in 16.7) 7 per cent (1 in 14.3) 3 Steep terrain up to 3000m height above mean sea level 6 per cent (1 in 16.7) 7 per cent (1 in 14.3) 8 per cent (1 in 12.5) Table: 1 Gradients for roads in different terrains
- 150. • Gradient up to the ruling gradient may be used as a matter of course in design. • For isolated bridges in flat country or roads carrying a large volume of slow moving traffic , it will be desirable to adopt a flatter gradient of 2 per cent fro the angle of aesthetics, traffic operations, and safety. • The limiting gradients may be used where the topography of a place compels this course or where the adoption of gentler gradients would add enormously to the cost. In such cases, the length of continuous grade steeper than the ruling gradient should be as short as possible.
- 151. • Exceptional gradients are meant to be adopted only in very difficult situations and for short lengths not exceeding 100m at a stretch. • In mountainous and steep terrain, successive stretches of exceptional gradients must be separated by a minimum length of 100m having gentler gradient.
- 152. • Grade compensation: When sharp horizontal curve is to be introduced on a road which has already the maximum permissible gradient, then the gradient should be decreased to compensate for the loss of tractive effort due to the curve. • This reduction in gradient at the horizontal curve is called grade compensation, which is intended to offset the extra tractive effort involved at the curve. 𝑅 • Grade compensation, per cent =30:𝑅 Or maximum value of 75 𝑅 • Where R is radius of the circular curve in meters
- 153. Vertical curves • Due to changes in grade in the vertical alignment of highway, it is necessary to introduce vertical curve at the intersections of different grades to smoothen out the vertical profile and thus ease off the changes in gradients for the fast moving vehicles. • The vertical curves are classified into two categories: 1. Summit curves or crest curves with convexity upwards. 2. Valley or sag curves with concavity upwards.
- 154. SUMMIT CURVERS: Types of summit curves Figure:1
- 155. • While designing the length of curves , it is necessary to consider the stopping sight distance(SSD) and overtaking sight distance (OSD) separately. For SSD: Case 1: When the length of the curve is greater than the sight distance (L ˃ SSD) Length of summit curves: L = 𝑁𝑆2 2𝐻: 2 2 As per IRC standard- H = 1.2; h = 0.15 then L = 𝑁𝑆2 4.4
- 156. Case 2: When the length of the curve is lesser than the sight distance (L < SSD) L = 2S - 2𝐻: 2 2 𝑁 As per IRC standard- H = 1.2; h = 0.15 then L =2S - 4.4 𝑁
- 157. For OSD: Case 1: When the length of the curve is greater than the overtaking or Intermediate sight distance (L ˃ S) L = 𝑁𝑆2 8𝐻 As per IRC : H = 1.2 m Then L = 𝑁𝑆2 9.6 Case 2: When the length of the curve is lesser than the overtaking or Intermediate sight distance (L ˃ S) L = 2S − 8𝐻 N As per IRC : H = 1.2 m Then L =2s - 9.6 𝑁
- 158. Design speed (kmph) Maximum grade change (% ) Minimum length of vertical curve, m 35 1.5 15 40 1.2 20 50 1.0 30 65 0.8 40 80 0.6 50 100 0.5 60 Minimum length of vertical curves as per IRC Table: 2
- 159. Valley curves: Types of Valley curves Figure: 4
- 160. The most important factors considered in valley curve design: 1. impact-free movement of vehicles at design speed or the comfort to the passengers 2. availability of stopping sight distance under head lights of vehicles for night driving. Length of valley curves: • The length of valley curve is designed based on the two criteria: 1. The allowable rate of change of centrifugal acceleration of 0.06 m/sec3 2. the head light sight distance, and the higher of the two values is adopted.
- 161. The valley curve is made fully transitional by providing two similar transition curves of equal length. Transition curve is set out by cubic parabola. Length of valley curve: case 1: when length of curve is greater than the sight distance Figure: 5
- 162. Case 2: When length is lesser than the sight distance. Figure: 6
- 164. Coordination of Vertical and Horizontal Alignment & Hairpin Bends
- 165. • Horizontal and vertical geometry must be designed concurrently. • Good coordination increases efficiency, safety, encourages uniform speed and improves appearance – without additional cost • Coordination must be addressed at earliest stage of design. • Driver sees road as changing 3D continuum and is distorted by sharp changes in design elements, cross sectional views and terrain.
- 166. Factors to be considered • The following should be considered in the coordination of horizontal and vertical alignment: o Balance Curvature and grades should be in proper balance. Maximum horizontal curvature with flat grades or flat curvature with maximum grades is undesirable. A compromise between the two extremes produces the best design relative to safety, capacity, ease and uniformity of operations and a pleasing appearance.
- 167. o Coordination Vertical curvature superimposed upon horizontal curvature generally results in a more pleasing appearance and reduces the number of sight distance restrictions. However, under some circumstances, superimposing the horizontal and vertical alignment must be tempered as mentioned below: Crest Vertical Curves. Sharp horizontal curvature should not be introduced at or near the top of pronounced crest vertical curves. Driver cannot perceive the horizontal change in alignment, especially at night when headlight beams project straight ahead into space. This problem can be avoided if the horizontal curvature leads the vertical curvature. Sag Vertical Curves. Sharp horizontal curvature should not be introduced near bottom of steep grade near the low point of a pronounced sag vertical curve Horizontal curves appear distorted Vehicle speeds (esp. trucks) are highest at the bottom of a sag vertical curve Can result in erratic motion
- 168. o Aesthetics When possible, alignment should enhance the scenic views of the natural and manmade environment. Highway should lead into, not away from outstanding views Fall towards features of interest at low elevation Rise towards features best seen from below or in silhouette against the sky
- 180. HAIRPIN BEND
- 181. Hairpin Bend • A hairpin bend is a road with a very acute inner angle, making it necessary for an oncoming vehicle to turn almost 1800 to continue on the road. • Hairpin turns are often provided when a route climbs up or down a steep slope ,so that it can travel mostly across with only moderate steepness and • Often arrayed in a zigzag pattern. • Highways with repeating hairpin turns allow easier, safer ascends and descends of mountainous terrain than a direct , steep climb and descend at the price of greater distances of travel and usually lower speed limits , due to sharpness of the turn.
- 182. Hairpin bend (Wayanad, Kerala)
- 183. Design Criteria as per IRC 52
- 184. IRC Recommendations for Hairpin bends • A hairpin bend may be designed as a circular curve with transition curves at each end. Alternatively compound circular curve may be provided. • Inner and outer edges of the roadway should be concentric with respect to centre line of the pavement. • Where a number of hairpin bends have to be introduced, a minimum intervening length of 60 m should be provided between successive bends to enable driver to negotiate the alignment smoothly.
- 185. THANK YOU 186