Improving transportation investment decisions through life cycle cost analysis: comparative LCCA of bridges

University essay from Luleå tekniska universitet/Samhällsbyggnad/Byggkonstruktion

Abstract: The aim and scope of the project is to study and apply Life Cycle Cost Analysis (LCCA) to standard bridges with a length of ca 20 m. Eleven bridges of reinforced concrete in northern Sweden have been studied with data from BaTMan, a Swedish bridge data base. Two alternative designs with timber (Glulam) and soil-steel (SuperCor) have also been studied. The concept of Present Value Method, Annuity Cost, and Societal Costs are described and the importance is discussed of parameters such as inflation and interest rates. In the analysis the following choices were made: interest rate 4 % and inflation rates for Maintenance, Repair and Rehabilitation (MR&R) 1,5%, for planning and design 2%, for dismantling 3% and for user's costs 5%. Methods are described for calculating user costs and for performing traffic analysis with a Swedish model called Sampers. Historical data and forecasts are presented.A sensitivity analysis is performed to understand how and how much the parameters involved in the analysis influence the final result. The life cycle costs for the eleven bridges vary between 4 and 20 Mkr and their annuity costs between 7 and 39 kkr. The lower costs refer to bridges with low initial investment (2,5 Mkr) and low traffic (20 vehicles/day), whereas the higher costs refer to bridges with high initial investment (11 Mkr) and high traffic (5000 vehicles/day). Of the life cycle costs, initial investments are 45 – 84%, user costs are 0,6 – 47%, maintenance, repair and rehabilitation (MR&R) are 4 – 14 %, dismantling are 1,4 – 5,6% and planning and design costs are 0,7 – 3,8%. Bridge designs with timber and soil-steel (SuperCor) are presented based on information collected from producers. LCCA has then been performed for three scenarios with different traffic volumes (100, 500 and 5000 vehicles per day in 2009), which reflect the situation in different Swedish regions. The estimated life cycle costs for the three scenarios are 2,3 Mkr, 2,4 Mkr and 4,4 Mkr for the soil-steel bridges and 2,5 Mkr, 2,7 Mkr and 4,7 Mkr for the timber bridges respectively. The annuity costs are 9 kkr, 9 kkr and 17 kkr for the soil-steel bridges and 10 kkr, 11 kkr and 19 kkr for the timber bridges respectively.The main conclusions from the project are that initial costs, user costs and life length have the highest influence on the life cycle costs and the annuity costs. Furthermore there exist no unique type of bridge that can be seen as the most cost efficient one. Rather, the economic efficiency depends on the location of the bridge and on the traffic volumes in that particular area. Future development is needed regarding data and stochastic and other models for forecasting of traffic, interest rates and inflation rates. Data bases need to be updated with initial costs, MR&R and life lengths for various bridge designs. Finally improved, user friendly software for LCCA would improve the beneficial use of this important concept for transportation investment decisions.