» Camber or cant or cross slope is the cross slope providedto raise middle of the road surface in the transversedirection to drain off rain water from road surface

» Objectives of providing camber are:

˃ Quick drying of pavement.

˃ Surface protection.

˃ Subgrade protection.

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IRC VALUES FOR CAMBER

SURFACE HEAVY LIGHT

TYPE RAIN RAIN

CONCRETE/BITUMINOUS 2 % 1.7 %

GRAVEL/WBM 3 % 2.5 %

EARTHEN 4 % 3.0 %

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» The safe and efficient operation of vehicles on the roaddepends very much on the visibility of the road ahead ofthe driver. Thus the geometric design of the road shouldbe done such that any obstruction on the road lengthcould be visible to the driver from some distance ahead .This distance is said to be the sight distance.

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Types of sight distance

Three sight distance situations are considered for design:

1. Stopping sight distance (SSD) or the absolute minimum sight distance

2. Intermediate sight distance (ISD) is defined as twice SSD

3. Overtaking sight distance (OSD) for safe overtaking operation

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Stopping sight distanceStopping sight distance (SSD) is the minimum sight

distance available on a highway at any spot having sufficientlength to enable the driver to stop a vehicle traveling atdesign speed, safely without collision with any otherobstruction.

Over-taking sight distanceThe overtaking sight distance is the minimum distance

open to the vision of the driver of a vehicle intending toovertake the slow vehicle ahead safely against the traffic inthe opposite direction.

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» Super-elevation or cant or banking is the transverse slopeprovided at horizontal curve to counteract the centrifugalforce, by raising the outer edge of the pavement withrespect to the inner edge, throughout the length of thehorizontal curve. When the outer edge is raised, acomponent of the curve weight will be complimented incounteracting the effect of centrifugal force

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Forces acting on a vehicle on horizontal curve of radius at a speed of are:

• the centrifugal force acting horizontally out-wards through the center of

gravity,

• the weight of the vehicle acting down-wards through the center of gravity,

and

• the friction force between the wheels and the pavement, along the surface

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» The position or the layout of the central line of thehighway on the ground is called the alignment.

» There are two types of alignment˃ Horizontal alignment includes straight and curved paths.

˃ Vertical alignment includes level and gradients.

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» Alignment decision is important because a bad alignmentwill enhance the construction, maintenance and vehicleoperating costs.

» Once an alignment is fixed and constructed, it is not easyto change it due to increase in cost of adjoining land andconstruction of costly structures by the roadside.

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» The alignment between two terminal stations should beshort and straight.

» The alignment should be easy to construct and maintain.It should be easy for the operation of vehicles.

» It should be safe both from the construction andoperating point of view especially at slopes,embankments, and cutting.

» The alignment should be economical and it can beconsidered so only when the initial cost, maintenancecost, and operating cost are minimum.

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» Horizontal alignment is one of the most importantfeatures influencing the efficiency and safety of a highway

» A poor design will result in lower speeds and resultantreduction in highway performance in terms of safety andcomfort. In addition, it may increase the cost of vehicleoperations and lower the highway capacity.

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» Transition curve is provided to change the horizontalalignment from straight to circular curve gradually andhas a radius which decreases from infinity at the straightend to the desired radius of the circular curve at the otherend.

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» OBJECTIVE OF PROVIDING TRANSITION CURVE

» To enable the driver turn the steering gradually for his own comfort and security

» To provide gradual introduction of super elevation

» To provide gradual introduction of extra widening.

» To enhance the aesthetic appearance of the road.

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» Extra widening refers to the additional width of carriageway that is required on a curved section of a road over and above that required on a straight alignment.

» This widening is done due to two reasons: the first and most important is the additional width required for a vehicle taking a horizontal curve and the second is due to the tendency of the drivers to ply away from the edge of the carriageway as they drive on a curve.

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