IN MANY DEVELOPING COUNTRIES. a considerable part of the intercity road network has pavement less than eighteen feet wide and much of it may be only twelve feet wide.A highway department wants to instruct the district offices regarding the optimum timing for widening the pavement to twenty feet. Aithough in developed countries the standard pavement width of a two-lane road is usually twenty-four feet, twenty feet is quite adequate to allow trucks and buses to pass each other comfortably and remain on the pavement. Although the capacity of a twenty-four-foot pavement is greater than that of a twenty -foot pavement,this difference is not relevant for the traffic volumes that are typical in developing countries and are used in this case study.