"Geometric Design Of HighwaysGEOMETRIC DESIGN ? Geometric Design for transportation facilitiesincludes the design of geometric cross section,horizontal alignment, vertical alignment,intersections, and various design details. ? The geometrics of highway should be designedto provide optimum efficiency in trafficoperations with maximum safety at reasonablecost.FACTORS DEPENDS ON GEOMETRIC DESIGN ? Design Speed ? Topography ? Traffic factors ? Design hourly volume and capacity ? Environmental and other factorsGEOMETRIC OF HIGHWAYS DEALS WITHFOLLOWING ELEMENTS: ? Cross section elements ? Sight distance consideration ? Horizontal Alignment details ? Vertical Alignment details ? Intersection elementsHIGHWAY CROSS SECTION ELEMENTS ? Pavement surface characteristics. ? Cross slope or Camber. ? Width of pavement or carriageway. ? Kerbs. ? Road margins.?PAVEMENT SURFACE CHARACTERISTICS : The pavement surface depends on the pavement type which is decided basedon the availability of materials and funds, volume and composition of traffic,subgrade, climatic conditions, construction facilities and costconsiderations. The important surface characteristics of the pavementare ------------- ? FRICTION ? PAVEMENT UNEVENNESS ? LIGHTREFLECTINGCHARACTERISTICS?FRICTION: (NOT AVAILABLE IN DEMO) ? Counteracts centrifugal force and governs the safe operating speed. ? Importantfactor in the acceleration & retardation of vehicles. ? Two important concept comes in this topic is SKID & SLIP SKID SLIP SLIP occurs when a wheel revolves moreLONGITUDINAL SKIDDING: than the corresponding longitudinalLongitudinal skid occurs when the brakesmovement along the roads. are applied, the wheels are lockedpartially or fully and vehicles moveIt generally occurs when the pavement is forward. slippery or wet. LATERAL SKIDDING: In horizontal curve when centrifugal forceis greater than counteracting force thenlateral skidding take placePAVEMENT UNEVENNESS: Higher speed operations are possible on even pavementwith less undulations than on uneven and poor surfaces. Causes of uneven pavement:- ? Inadequate or improper compaction of the fill, subgrade &pavement layers ? Using boulder stones and bricks unscientifically ? Improper surface and sub surface drainage ? Use of improper construction machineries ? Lack of maintenanceCROSS SLOPE OR CAMBER : (NOT AVAILABLE INDEMO) It is used to prevent the entry of surface water and rainwater into the sub grade soil and bituminouspavement layers.WIDTH OF PAVEMENT AND KERBS:(NOTAVAILABLE IN DEMO) As per Indian Road Congress (IRC) CLASS OF ROAD WIDTH OFCARRIAGEWAY Single lane 3.75m Two lanes, 7.0m without raisedkerbs Two lanes with 7.5m raised kerbs Intermediate 5.5m carriageway Multi-lane 3.5m per lane pavementsFull presentation available in original version?STOPPING SIGHT DISTANCE (SSD) The minimum sight distance available on a highway at any spot should be sufficientlength to stop a vehicle traveling at design speed, safely without collision withany other obstruction is known as SSD. SSD depends upon the following factors-------- ? Total reaction time of the driver ? Speed of vehicle ? Efficiency of brakes ? Frictional resistance between the road and the tyres ? Gradient of the road, If anyCALCULATION OF OSD OSD for one way traffic= d1+d2 OSD for two way traffic= d1+d2+d3 [d1= v x t, v=speed of overtaken vehicle t= reaction time= 2 seconds d2= 2s+b By emperical formula, S= (0.6v+6)meter b= v x T ;T= sqrt of (4s/a) a= acceleration of vehicle D3 = V x T V= design speed Min. overtaking zone= 3 x OSDHORIZONTAL ALIGNMENT Changes in direction in highway alignment due toobligatory point leads us to this concept. Elements in Horizontal alignment ? Design speed. ? Horizontal curves. ? Super elevation. ? Widening of pavement. ? Horizontal transition curve. ? Set-back distance.SUPERELEVATION To counteract the effect of centrifugal force and to reduce thetendency of the vehicle to overturn or skid."