1. Highway Alignment And Geometric Design
Prepared by
Wrya H.Nadir

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

3. 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. .

4. 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.

5. 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

6. Type Of Horizontal Alignment
1-Circular Curves:
simple

7. 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

8. 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,

9. Elements Of Spiral Curves

10. Continue….

11. 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

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

13. 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

14. 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

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

17. Thank For All