ROAD CAPACITY AND DESIGN OF PAVEMENTS

The useful life of a road depends upon-- The type of construction (road structure) , intensity and nature of the traffic, bearing capacity of the sub grade (soil) , climate conditions and maintenance behavior. A properly constructed water bound macadam road will carry suitable medium weight vehicles without excessive maintenance, where in a bitumen grouted macadam better than water bound macadam but water bound macadam road is not considered suitable for traffic. Heavy mixed traffic and the adverse weather condition damage the water bound macadam roads where the rain water wash away the soil binder and the stone aggregates protude out or get loose on the surface layer thus forming pot holes and ruts. It is necessary to maintain the roads timely and make it fit for the vehicular traffic where it must be realised that it is the sub grade which really carries the weight of the vehicles and that the function of the road surface (road structure) is merely to distribute that weight over a larger area and if the sub grade is composed of the unsuitable material or if the water has access to it, the earth underneath will move and the road surface will fail, hence the character of the sub grade has a great effect upon the stability of the road surface. Therefore a study of the soil structure is a very important factor for the required good roads. The design of the pavement is governed by the traffic density ie the number of vehicles using the road during the peak hours, and the maximum wheel load. The daily traffic volume is about 8 to 10 times the maximum hourly volume. Character of the traffic and the speed of the vehicles are also major considerations. Rate of traffic increase per annum is also to be considered and which may vary from 10 to 20 percent in a developing country like India . Road capacity depends upon the type of roads where single lane, 3.75 m carriage way with earth shoulders designed for 1000 , Single lane with hard shoulders 1.0 m wide capacity 2500 , Two lane, 7 m carriage way, 10000 , 5.5 m carriage way-- 5000 and four lane divided highway-- 20000 to 30000 . It is traffic count equivalency factor for vehicles per day (both directions) Since the road traffic is composed of different types of vehicles, it is converted into equivalent passenger car unit for counting for which Equivalency factor for passenger car, tempo, autorikshaw is -- 1.0 , Cycle, motor cycle or scooter --0. 5 , Truck, bus, tractor-trailor unit --3. 0 , Cycle rickshaw--1. 5 , Horse drawn vehicle--4. 0 and Bulkack cart -- 6to 8.0 . It is therefore necessary to follow the above guidelines and recommendations of the code for consideration based on IRC :52 -1981& 70 -1977:--- Er Fateh Chand Guleria, Director RTI welfare Association registered number HPCD 3552 , Bilaspur Himachal Pradesh phone number 9459334377