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Highway Network Design Manual

Highway Network Design Manual



Road Slopes

Superelevation

This concept deals with the horizontal or lateral (cross) slope of a roadway. Superelevation of a roadway is used in order to accomplish two objectives: to provide adequate drainage flow for water on the roadway surface and to aid in steering of motor vehicles on curved roadways.
In a tangent section, a common superelevation or cross slope of 1-2% is applied in order to achieve drainage flow of surface water off of the subject roadway.
In a curved section, calculated super elevations generally reaching a maximum of 6 or 8% (depending on selected design criteria) are applied in order to aid motorists in safely traversing these sections while maintaining entry speed of the vehicle along the length of the curve.

Cross Slope

The maximum algebraic difference in cross slope between same direction traffic lanes of divided highway roadbeds should be 4%.

The maximum difference in cross slope between the traveled way and the shoulder should not exceed 8%. This applies to new construction as well as pavement overlay projects.

The American Association of State Highway and Transportation officials (AASHTO) provides a table from which desired superelevation rates can be easily interpolated based on the prescribed magnitudes for both design speed and radius of a curved section of roadway

Profile Designing Management

Profile Designing Management.

Vertical curves are used to provide a gradual change from one road slope to another, so that vehicles may smoothly navigate grade changes as they travel.

Vertical Curves
Where is a vertical curve required
Where the algebric difference of two grade is greater than 0.5%
Where the algebraic difference in grades is 0.5% or less there curve is not required.

 

The Minimum Length of Vertical Curves

The minimum length of vertical curve in meters should be equal to 2V,

Where V = design speed.

As an example, a 100 km/h design speed would require a 200 m minimum vertical curve length.

As per AASHTO for the speed of 60 km /h
Minimum curve length is required 36m
And K is required 11
And stopping distance required 85 m

Grade breaks should not be closer together than 15 m and a total of all grade breaks within 60 m should not exceed 0.5%.

Polygon Solve

Polygon Solving formulas of MS Excel

Right Triangle Formula

Right Triangle Formula of calculation for excel

Circle segment formula

Circle segments calculation formula in excel

Horizontal Alignment

Horizontal Curves

For central angles smaller than 30 minutes, no curve is required.

The minimum curve length for central angles less than 10 degrees should be 240 m to avoid the appearance of a kink.

Above a 6000 m radius, a parabolic curve may be used. In no event should sight distance or other safety considerations be sacrificed to meet the above requirements.

ATTRIBUTES OF HORIZONTAL ALIGNMENT
Factors Influencing the Selection of Horizontal Alignment

 General Criteria
 Sight Distance Measurements for Horizontal Curves
 Horizontal & Vertical Alignment Coordination
 Striping No-Passing Zones 
 Intersecting Roads
 Utilities
 Transition (Spiral Curves)
 Circular Curves
 Superelevation
      Superelevation Transitions    
     Sample Calculation
     Superelevation Transition for 2 Lane Highway
     Rural Low Speed
     Urban Low Speed
     High Speed
     Superelevation Transition for Divided Highways
     Maximum Relative Gradient (English)
     Maximum Relative Gradient (Metric)
 Traffic Diversion Alignment
     Traffic Diversion Design