This Article Covers What Is Summit Curves, Design Criteria, Length And Types One By One.
Summit curves are the vertical curves having convexity upwards, These curves introduced for the driving comfort and aesthetic purposes.
In summit curves we do not need any transition curves because centrifugal acceleration is not acting laterally outward or inward but, its acting upward.
The summit curve is one type of the vertical curve, It is provided on the highway or railway when it crossed ridge or valley.
Generally, this curve is determine by parabolic equation.
There is basic condition that need to satisfied for summit curve.
The condition is as follow
- There must be constant rate of change of grade.
- Parabola fulfill this and so summit curve is mainly parabolic type.
As we know that there is two types of vertical curve, in that the curve that is convexity of upward that known as the summit curve.
Types of summit Curve
- The common practice has been to use parabolic curves in summit curves. This is primarily because of the ease with it can laid out as well as allowing a comfortable transition from one gradient to another.
- Circular curve offers equal sight distance at every point on the curve, for very small deviation angles a circular curve and parabolic curves are almost congruent.
Design of Vertical Summit Curve
Summit curves are those curves which have convexity upwards, They formed under the four following conditions:
- When a positive gradient meets another mild positive gradient.
- And When a positive gradient meets a level zero gradient.
- When a positive gradient meets with a negative gradient.
- When a negative gradient meets another steeper negative gradient.
During the design of vertical summit curve the comfort, appearance, and security of the driver should considered.
The sight distance must considered in the design.
All the types of sight distance should considered during design as far as possible.
During movement in a summit curve, there is less discomfort to the passengers because the centrifugal force developed by the movement of the vehicle on a summit curve act upwards which is opposite to the direction in which its weight acts.
This relieves the load on the springs of the vehicle so stress developed will be less.
A simple parabolic curve preferred in summit curve due to its easy implementation in the field, good riding comfort during driving and easy computation.
The important part in summit curve design is the computation of the length of the summit curve.
Length of Summit Curve
The length of the summit curve designed based on
- Considering the stopping sight distance.
- To Considering the safe overtaking sight distance or intermediate sight distance.
Considering the Stopping Sight Distance
The length of summit curve(L) according to this criteria may determined in following two conditions:-
- When the total length of the summit curve (L) is greater than the stopping sight distance(S), the value of L (length of summit curve) calculated by L = NS2 /(√2H + √2h)2
- When the total length of the summit curve (L) is less than the stopping sight distance, the value of L(length of summit curve) calculated by L = 2S – (√2H + √2h)2 /N
H = is the height of eye level of the driver above the roadway surface in m.
h = is the height of the object above the pavement surface in m and N is the deviation angle.
Considering the safe overtaking sight distance or intermediate sight distance
The length of summit curve(L) according to this criteria may determined for the two conditions:-
When the total length of the summit curve (L) is greater than the overtaking or intermediate sight distance (S), the value of L calculated by L = NS2/8H
When the total length of the summit curve (L) is less than the overtaking or intermediate sight distance (S), the value of L calculated by L = 2S – 8H/N
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