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Eng. Haytham Besaiso
Cross Slope (Camber)
It is the slope of the roadway lanes in the straight line (Tangent)
portion of the horizontal alignment, and its value is taken as following:-
1. qmin =2.5 % (Germany Guidelines)
2. qmin =1.5 % (AASHTO and BS Guidelines)
The shape of the cross slope according to the number of lanes is as
following :-
2-lanes undivided :- lanes divided:-
4-lanes undivided:- 4-lanes divided :-
Curvature Diagram
It is used to know the centrifugal force affecting the vehicle
travelling on curves as a measure of severity of horizontal curves.
1. for straight line R=∞ , K= ∞
1 =0
2. for circular curve R=Rc , K= 1/Rc
3. for transition curve ∞ < R < Rc , 0<K<1/R
The curvature to the right is +ve
The curvature to the left is – ve
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Eng. Haytham Besaiso
Example 1 : Assume R1 < R2
Example 2 : Assume Rc1<Rc2
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Eng. Haytham Besaiso
Note:
• The horizontal axis represents the actual length of the horizontal
alignment and not the projected length .
• Which curvature has a positive value and which has a negative value ?
Firstly, define the direction of traffic flow (for divided highways) or the
direction of stations increase (undivided highway). Then consider the sign
convention which states that the curve with the right center is positive and
the curve with the left center is negative.
Superelevation Superelevation is the banking of the roadway along a horizontal curve so
that the drivers can negotiate the curve at safe and comfortable speed.
Relationship between speed v, e, f, and curve radius, R
From the laws of mechanics, the basic curve formula that governs
vehicle operation on a curve is
e = rate of roadway superelevation, percent;
f = side friction factor;
v = vehicle speed, m/s;
g = gravitational constant, 9.81 m/s2;
V = vehicle speed, km/h;
R = radius of curve, m
In practice, and g is calculated, so the equation
reduces to the simplified design formula
101.01 ≈− ef
fR
ve −=
12701.0
2
gR
v
ef
fe 2
01.01
01.0=
−
+
Eng. Haytham Besaiso
Methods of attaining superelevation
1. rotation about centerline
2. rotate about inner edge
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Methods of attaining superelevation
rotation about centerline
rotate about inner edge
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Eng. Haytham Besaiso
Draw the superelevation diagram for the following alignment
RHS : - - - - - - LHS : __________
Example 1
Example 2
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Eng. Haytham Besaiso
Notes:
1. Before drawing the superelevation diagram, define the direction of
traffic flow or stations increase to be able to differentiate between the
right edge and the left edge of the road.
2. Try to avoid the locations of rain water accumulation (bad drainage)