Highway Alignment And Geometric Design Prepared by Wrya H.Nadir

Content Introduction Horizontal alignment Type of horizontal alignment Parts of circular curve Parts of transition curve Superelevation Method of building superelevation

Introduction highway alignment is a three-dimensional problem represented in the X, Y, and Z coordinates Finding the dimensions of the geometric design elements of highway alignments is called geometric design Horizontal and vertical alignments are two major components of highway geometric design. .

General point for design Elements of geometric design 1-highway alignment: horizontal and vertical alignment 2-sight distance: SSD PSD DSD 3-widening on curve 4-superelevation 5-transition curves 6-intersection 7-highway cross section 1-Estimated future traffic volume(ADT.AADT). 2-Must be safe for driving. 3-Avoid surprise change in direction, grade site distance. 4-Design must be completed. 5-Must be economical as possible.

Horizontal Alignment The horizontal alignment of a highway is the plan view of the route. It consists of straight sections (tangents) of the roadway connected by curves. Necessary for gradual change in direction when a direct point of intersection is not feasible Tangent line H. Curves

Type Of Horizontal Alignment 1-Circular Curves: simple

Parts Of Circular Curves =Middle ordinate =long chord =tangent =External distance =Length of curve PI: point of intersection :intersection angle R: Radius of curve PC: Point of curvature PT: point of tangency

Continue….. 2-Transition Curves: a-spiral or clothoid b-cubic spiral c-cubic parabola d- lemniscates Function: 1-to introduce gradually centrifugal force between the tangent point and the beginning of the circular curve avoiding a sudden jerk on the vehicle 2-to enable the driver turn steering gradually for his own comfort and security. 3-to enable gradual introduction of the designed super elevation and extra widening,

Elements Of Spiral Curves

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Super Elevation Superelevation is tilting the roadway to help centrifugal force developed as the vehicle goes around a curve. Along with friction. it is what keeps a vehicle from going off the road. Must be done gradually over a distance without noticeable reduction in speed or safety

Continue…. V:Design Speed Km/H R:Radius Of Curve e:Seper Elevation fs: Coefficient Of Friction Between The Tire And Road Surface

Min and Max (e)with (fs) Max(e)=0.07=7%: plain and rolling terrain and mountains and steep terrain bounded by snow. Max(e)=0.1=1%:for mountains and steep terrain not bounded by snow. 1/8 for non snow condition AASHTO Max(e) = 1/1.6 for snow condition Min(e)=2%(cross slope of the road(camber)) 0.2 for muddy roads . Fs= 0.15 for newly constructed asphalt roads. Depend on the : 1-presence of water(moisture),mud, snow 2-condition of tread design and air pressure of tyres

Superelevation Transitions Consist Of Tangent Runout And Superelevation Runoff Section. Runout: length of roadway needed to accomplished a change in outside lane cross slope from normal rate to zero Runoff: length of roadway needed to accomplished a change in outside lane cross slope from zero to full

Methods Of Building Seperelevation 1-center Line Revolving Pavement About 2- Inner Edge 3-outer Edge

Thank For All