CBR METHOD OF DESIGN IS BASED ON THE COMPUTATION OF TRAFFIC CENSUS

CBR METHOD OF DESIGN :-- A surface having a CBR of 100 percent is one in which a load of 1360 kg has to be exerted to drive in a cylindrical flate plunger with a base area of 19.3 square cm to a distance of 0.250 mm at the rate of penetration of 0.125mm per minute. The computation of traffic for the use of CBR over the carriage way considered in units of the commercial vehicles for different classification of roads:-- In the case of single lane roads 3.75 mt wide the design is based on the total number of commercial vehicles per day in both directions multiplied by two .In case of intermediate width roads (5.5 mt width ) the design should be based on the total number of commercial vehicles per day in both directions multiplied by 1.5 Two lane single carriage way roads the design is based on 75 percent of the total number of commercial vehicles in both directions. Where as four lane single carriage way roads are designed on the basis of 40 percent of the total number of commercial vehicles in both directions. As for as the dual two lane carriage way design of roads is concerned it should be based on 75 percent of the number of commercial vehicles in each direction and the distribution factor shall be reduced by 20 percent for each additional lane .