They are expected to function properly by providing a smooth traveling surface for the traffic under various conditions of the environment. Like other engineered structures, designed pavements are expected to be adequately strong and durable for their design life. The development of a country is often judged in terms of its total paved road. Surface transportation is the most widely used mode of transportation, and pavements are an essential part of roads, streets, and parking lots in all over the world. Also it was shown that, with increasing the strength of subgrade soil, the subbase layer may be removed from the optimum structure of pavement.

Design charts confirm that in the current situation (material prices in 2015), application of asphalt treated layer in pavement structure is not cost effective.

After developing the optimization model, the optimum thickness of pavement layers for secondary rural roads, major rural roads, and freeways was determined based on the recommended prices in “Basic Price List for Road, Runway and Railway” of Iran in 2015 and several charts were developed to determine the optimum thickness of pavement layers including asphalt concrete, granular base, and granular subbase with respect to road classification, design traffic, and resilient modulus of subgrade. This paper aims to propose an optimization model to determine the optimal configuration as well as the optimum thickness of different pavement layers based on the Iran Highway Asphalt Paving Code Number 234 (IHAP Code 234). Incommensurate design and construction of pavements, in addition to the loss of the initial investment, would impose indirect costs to the road users and reduce road safety. Pavement construction is one of the most costly parts of transportation infrastructures.

Pavement design aashto method proposals