This paper presents some results obtained in the Infravation research project called 'Fast and effective solution for steel bridges life-time extension' (FASSTbridge). The aim of this project is to develop and demonstrate a reliable, preventive, cost-effective and sustainable solution for steel bridges fatigue life-time extension. Original sustainable preventive strengthening techniques will be tested to help postpone difficult, resource-consuming and costly retrofitting and repair interventions and demolitions of the steel and composite steel bridges stock. This paper addresses the definition of the needed data and the methodology for the realization of an actual cost-benefit analysis and a life cycle analysis of the CFRP solution compared with traditional techniques (use of steel plates) and considering the economic and environmental profit of the preventing policy.