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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)