# Horizontal Alignment Design Speed & Horizontal curve

This Article Covers Horizontal Alignment Their Design Speed And Horizontal Curves Briefly One By One.

## Horizontal Alignment

The Horizontal alignment is one of the most important features influencing the efficiency and safety of a highway. Horizontal alignment design involves the understanding on the design aspects such as design speed and the effect of horizontal curve on the vehicles.

The horizontal curve design elements include design of super elevation, extra widening at horizontal curves, design of transition curve, and set back distance.

### Design Speed

The design speed as noted earlier, is the single most important factor in the design of horizontal alignment. The design speed also depends on the type of the road.

For e.g, the design speed expected from a National highway will be much higher than a village road, and hence the curve geometry will vary significantly.

#### Factors Affecting Alignment

1. Safety
2. Grades
3. Design speed
4. Cost of resumption of land
5. Construction costs

Operating speed is influenced by all other factors so it is the critical factor to consider.

### Horizontal Curve

The presence of horizontal curve imparts centrifugal force which is reactive force acting outward on a vehicle negotiating it. Centrifugal force depends on speed and radius of the horizontal curve and is counteracted to a certain extent by transverse friction between the tyre and pavement surface.

On a curved road, this force tends to cause the vehicle to overrun or to slide outward from the centre of road curvature. For proper design of the curve, an understanding of the forces acting on a vehicle taking a horizontal curve is necessary.

P the centrifugal force acting horizontally out-wards through the center of gravity, W the weight of the vehicle acting down-wards through the center of gravity, and mF the friction force between the wheels and the pavement, along the surface inward.

At equilibrium, by resolving the forces parallel to the surface of the pavement we get,

P cos = W sin + FA + FB
= W sin + f (RA + RB )
= W sin + f (W cos + P sin )

Next Article We Covers Design Of Super Elevation.

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Also Check Video Tutorial Site KPSTRUCTURES.COM

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