CROSS SECTIONAL ELEMENTS OF HIGHWAY.
Cross sectional elements of Highway
1. Unevenness.
2 . Light reflection.
3. Drainage.
4. Camber. ...
5. Width of carriage way.
6. Kerbs.
1. Unevenness
It is always desirable to have an even surface, but it is seldom possible to have such one. Even if a road is constructed with high quality pavers, it is possible to develop unevenness due to pavement failures. Unevenness a ect the vehicle operating cost, speed, riding comfort, safety, fuel consumption and wear and tear of tyres.
Unevenness index is a measure of unevenness which is the cumulative measure of vertical undulation of the pavement surface recorded per unit horizontal length of the road.
An unevenness index value less than 1500 mm/km is considered as good, a value less than 2500mm/km is satisfactory up to speed of 100 kmph and values greater than 3200 mm/km is considered as uncomfortable even for 55 kmph.
2. Light reflection
Conventional pavements such as asphalt have a low albedo of around 0.05-0.1, meaning they reflect only 5% to 10% of the light they receive and absorb as much as 95%.
3. Drainage
The pavement surface should be absolutely impermeable to prevent seepage of water into the pavement layers. Further, both the geometry and texture of pavement surface should help in draining out the water from the surface in less time.
4. Camber
Camber or cant is the cross slope provided to raise middle of the road surface in the transverse direction to drain o rain water from road surface. Too steep slope is undesirable for it will erode the surface. Camber is measured in 1 in n or n% (Eg. 1 in 50 or 2%) and the value depends on the type of pavement surface.
5. Width of carriage way
Width of the carriage way or the width of the pavement depends on the width of the traffic lane and number of lanes. Width of a traffic lane depends on the width of the vehicle and the clearance. Side clearance improves operating speed and safety.
6. Kerbs
Kerbs indicate the boundary between the carriage way and the shoulder or islands or footpaths.
Different types of kerbs are:
(I) Low or mountable kerbs
(II) Semi-barrier type kerbs
(III) Barrier types kerbs
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