ABSTRACT
Pavement deterioration is revealed through many indications, among which is roughness of its surface which is a collective consequence of the various deterioration factors of the pavement. The economic impact of road deterioration is considerable, and usually outweighs the consideration of riding comfort, and thus providing the strongest objective for evaluating roads improvement policies and corresponding cost implications. This work attempts to address the effect of applying different strategies of overlay as remedies to arrest the escalation of costs incurred by both road agencies and users, and finally, determines the economic optimum strategy that minimize the total system cost. In order to effectively achieve this, six different strategies (the do nothing, 200mm,150mm 100mm,75mm, and 50mm) were investigated to reflect both service performance and economic evaluation. Relevant data for evaluating performance were collected from the pavement evaluation unit (PEU) of the Federal Ministry of Works, Kaduna and data concerning unit costs of road works were determined from the World Bank's "ROCKS" (Road cost knowledge system). The Highway Design and Maintenance Model (HDM III) was used in the analysis of the strategies. The model predicts the pavement deterioration and maintenance effects, and calculates annual costs of road construction, vehicle and operation, needed to perform the economic evaluation of the alteration. Results obtained show that, for all the strategies considered, road user cost exceeded all other costs and the strategy with the thickest overlay (i.e. 200mm) has the lowest road user cost of N33.4b. Also, the rate of deterioration was lowest for the 200mm strategy, and is also associated with the highest user 9 benefit N10.4b. On the other hand, the 75mm thick overlay strategy had the lowest Total Systems Cost (TSC) of N35.5b and the highest net present value (NPV) of N7.3b. The 75mm design strategy is therefore selected as the optimum strategy.