## 3 Vehicle Replacement Optimization Model
### Environmental Profiles of Life Cycle Phases  
LCA aims to assess the environmental burdens of a total life cycle and to determine how they are distributed over successive life cycle stages. The assessment is made based on a thorough inventory of flows important for the environment and all processes at all phases of the life cycle. These flows include used resources, emissions and pollution released to the environment in each elementary process/activity over the whole life cycle. The sizes of such flows are calculated as functional units. In LCA, the functional unit is usually the number of driven kilometers for an average car age and the annual average mileage, data published in public reports [2]. Owing to that, LCA gives a cumulative assessment score in a total given time horizon, which for example can cover the whole phase of car use determined in a study. This result does not give any idea of how burdens are distributed over smaller intervals of life cycles. The application of LCA for environmental optimization replacement models, which provide a long-term prognosis in a long planning horizon given changes of the initial state, requires a different arrangement of life cycle inventory (LCI) that defines production, use, maintenance and disposal. This applies in particular to modifications of car design which affect vehicle environmental performance in terms of material content and wear, energy efficiency and emission class. Reliability and the gradual car condition getting worse over time are important parameters. The effect of the maintenance stage is dependent on the former and the latter.  
The above presented description of why oil exchange intervals in diesel cars become shortened by a factor of several times demonstrates that some technical improvements which are supposed to improve exhaust gas emission control may at the same time significantly increase the impact of the maintenance phase. The arrangement of time variable parameters should allow an assessment of impact over small time intervals, with resolution necessary in research and available, for example, for every age or car mileage.  
The replacement optimization used LCA data from an earlier project from [PERSON] et al. [6]. That paper presents the procedures of data collection and impact assessment at successive stages of the life cycle. A thorough inventory was appended for publication. LCA calculations were made for the Ford Focus passenger car, which is representative of the medium-sized European ICEV. The car was modeled in two fuel versions (petrol and diesel) to be able to assess the environmental performance of different car technologies. The LCA results cover 151,200 km driven in typical European conditions. This is mostly consistent with the average annual mileage and average age of cars in the EU.  
This study focuses on the assessment of the impact maintenance has and its consequences for vehicle replacement policy. Therefore, previous study maintenance scenarios, modeled based on confidential data, will be discussed at a higher level of detail. A publicly available inventory from Ecoinvent version v3.5 [40] was used to model the other stages of the life cycle. The main modeling assumptions and results are presented below and discussed.