PAVEMENT TYPE SELECTION FOR DEVELOPING COUNTRIES APPLYING LIFE CYCLE COST ANALYSIS

pavement. In this research, Life Cycle Cost Analysisof flexible and rigid pavement had been done for Sylhet-Bholagajroad comprising of both rigid & flexible portions. The pavement design data & different Schedule of Rates collected from the Roads and Highways Departmenthad been used for this analysis. 12% discount rate was used to convert all estimated future costs to Net Present Value. After performing a life cycle cost analysis, it can be concluded that rigid pavement is the optimal choice of pavementfor developing countries like Bangladesh.

Road network acts as a vein for the socio-economicdevelopment of a country. To maintain sustainable development,countries all over the world are investing heavily in road network infrastructure development. Bangladesh, an essential partner of the Asian Highway, is alsoinvesting heavily in road network development. But due to poorplanning, inefficient implementing agencies, inadequate pavementdesign, lowquality construction practices, lack of pavementmaintenance, rampant overloading & tropical climaticconditions, the investment is not yielding the desired result. In Bangladesh, the current trend of pavement construction is 95% flexible pavement [16]. Due to tropical climatic conditions & regular flash floods during the rainy season, water stagnation damages the flexible pavements severely. The rigid pavement has a high potential of survivability against the damage due to water stagnation. In Bangladesh, the transportation agencies emphasize on least initial construction cost rather thanthe least Life Cycle Costas the only tool for pavement type selection. Due to low initial construction cost, the flexible pavement always gets priority over the rigid pavement. In this research, Life Cycle Cost Analysisof flexible and rigid pavement had been done for Sylhet-Bholagajroad comprising of both rigid & flexible portions. The pavement design data & different Schedule of Rates collected from the Roads and Highways Departmenthad been used for this analysis. 12% discount rate was used to convert all estimated future costs to Net Present Value. After performing a life cycle cost analysis, it can be concluded that rigid pavement is the optimal choice of pavementfor developing countries like Bangladesh.

…………………………………………………………………………………………………….... Introduction:-
Road infrastructure development and maintenance require significant capital investment. New road construction costs nearly 50% of the annual budget for transportation agencies in many developed countries. In comparison,Maintenance and Rehabilitation (M&R) of the existing road network costs the remaining 50% budget [12]. Bangladesh is a developing country, and around 15-20% of its annual budget for roads is spent onM&R programs [3]. A sustainable road transport infrastructure that requires the least possible M&R cost will boost the social, economic & cultural development of a country. Transportation agencies worldwide are involving themselves 315 in finding the appropriate pavement type that requires fewer recurring costs but meets the ever-increasing demands of road users, including comfortability, speed & safety [11]. Whether the flexible pavements are economically superior to rigid pavements or not over a long time is a historical debate. Even experienced transportation agencies & experts have different opinions on this subject [19]. For suitable pavement type selection, transportation agencies globally have started using tools & techniques [4]. The Life Cycle Cost Analysis (LCCA) is one of the tested tools based on economic analysis principles for the suitability of different long-term rivalling investment options [13]. The sustainability of national highways can be achieved by reducing pavement life cycle cost to a minimum [8]. Developed countries are using LCCA as a reliable mechanism for the construction and maintenance of bridges and highways. But in developing countries, very little utilization of LCCA is found. Only a few research works have been performed on the application of LCCA in developing countries [9]. This research aims to select the economically viable pavement type for developing countries like Bangladesh.

Literature Review:-
In 1960, AASHTO "Red Book" first discussed the possible application of LCCA in pavement construction [21]. In the USA, state transportation agencies must conduct LCCA of any project to justify their planning & actions while using federal funds. The mandate for the application of LCCA for pavement, bridge, or tunnel construction projects at both metropolitan and state level was made by 1991, Intermodal Surface Transportation Efficiency Act (TEA) [20]. National Highway System Designation act of 1995 requiredLCCA evaluation of all national highway projects costing $25 million or moreundertaken by any state. The federal executive order 12893, signed in 1994, mandated federal agencies to apply a systematic evaluation of costs and benefits for taking any development action [14]. Though the 1998 TEA withdrew the requirement of LCCA for transportation, still Federal Highway Administration encourages highway projects to be evaluated by LCCA before its implementation. LCCA is currently being used as a supporting tool for taking decisionsat the projectlevel. But recently,the application of LCCA has been started atthe networklevel [6]. "LCCA is an analysis tool based on the principles of economic analysis for evaluating long-term economic efficiency among rivalling investment options. This analysis incorporates costs of agency (initial costs and future M&R costs), user, and other related costs over the design life of alternative investment options. It emphasizes finding the best value investment option" [20].
LCCA is applied to select pavement type andselect rehabilitation strategies of existing pavements [18]. The application of LCCA ensures the selection of the most cost-effective solution and illustrates the factors that influence cost-effectiveness. Different types of costs incorporated in LCCA have been discussed in AASHTO Pavement Design Guidelines [1]. Pavement LCCA mainly focuses on agency costs, user costs &society costs [2]. The agency costs have been further subdivided into initial construction costs and M&R costs. The initial construction costs include the costs of pavement design, acquisition of land & construction of pavement.The M&R costs incorporate the costs of preservation, reconstruction, restoration & rehabilitation.User costs include the costs of vehicle operation, traffic delay & accidents. Social costs represent all the costs related to environmental degradation of the area surrounding the pavement. People living nearby have to bear social costs sometimes even without using the pavement facilities.
The LCCA period of both flexible and rigid pavement had been taken 20 years for this research. According to AASHTO Design Guidelines [1], flexible pavements require overlay after every 10 years. But flexible pavement in Bangladesh reaches its terminal serviceability within 05 years of construction due to overloading traffic stream & tropical climatic conditions. So, after every 05 years, an overlay is recommended for flexible pavements instead of 10 years [10]. For rigid pavement, there is no need for overlay during its 20 years design period. Due to poor recordkeeping in Bangladesh, the determination of costs associated with pavement M&R activities is very complex. Even the transportation agencies find difficulty in differentiating maintenance activities. To overcome this information deficiency, the maintenance cost estimation for flexible & rigid pavements had been adopted from the "Maintenance 316 and Rehabilitation Needs Report of 2019 -2020 for RHD Paved Roads" by RHD, Bangladesh [17]. The estimated maintenancecosts have been presented in table 1 below:   [4]. Because of simplicity and ease of use, NPV had been used in this research. The NPV is the present discounted monetary value of expected net benefits [20]. In NPV, all the associated costs are converted to a single time cost [15]. Equation 1 had been used for NPV calculation of future investments: NPVof future investment= ∑ Initial Cost × 1+i n 1+d n ………..……………..………………………….….Equation (1) Where, i is the economic growth rate in percentage d is the discount rate in percentage & n is the year of expenditure To convert all the futurecosts to NPV, a 7% growth rate & a 12% discount rate for the fiscal year 2019-2020 had been considered according to the Bangladesh Planning Commission's direction [5].
Site selection for Data collection LCC comparison between flexible pavement and rigid pavement requires that both the roads should have the same geometric profile & same soil characteristics over which they are built. Both the pavements should also carry similar traffic loadings. Several roads under RHD had been observed to meet these requirements, and only theSylhet-Bholagajroad project had been chosen as the suitable site. The road is a 30 km Zilla road consisting of a 17km flexible pavement while the rest of 13 km is rigid pavement.

Data Collection
The detailed pavement design data of Sylhet-Bholagaj road was obtained from the Technical Services Wing of RHD. The pavement has a two-lane single carriageway, each having a lane width of 4.9m. The design traffic data was collected from Sylhet, RHD. The pavement was designed assuming a 7% traffic growth rate, and the design life     So, after life cycle cost analysis, it can easily be said that though the initial construction cost of rigid pavement is always higher than the flexible pavement irrespective of the Schedule of Rates used, due to low M&R cost, the LCC of rigid pavement is much lesser than flexible pavement throughout its 20 years design period. For a developing country like Bangladesh, due to resource scarcity, transportation agencies should find a cost-effective, sustainable solution, and rigid pavement meets both the requirement [10].

Conclusion:-
The initial construction cost comparison based on Schedule of Rates 2019 & 2015 has revealed that rigid pavement is 25 % and 47% more expensive to build than flexible pavement, respectively. Initial construction cost is primarily dependent on materials costs. As materials price varies on availability, one country's initial construction cost comparison result might be totally different from another country. Ironically, most of the time, transportation agencies in developing countries decide based on initial construction cost only. But the life cycle cost comparison based on Schedule of Rates 2019 & 2015 has revealed that rigid pavement is 32 % and 14% less expensivethan flexible pavementthroughout its design period, respectively. The flexible pavement needs costly overlay every 5 years, making it costlier than rigid pavement though the initial construction cost comparison result was completely reverse. Based on the output of life cycle cost comparison between flexible and rigid pavement presented in this research, it can be concluded that rigid pavement is the optimal choice of pavementfor developingcountries like Bangladesh with tropical climatic conditions.