## 3 Vehicle Replacement Optimization Model  
### Assumptions  
The study by [PERSON] et al. [9] challenges the age of the vehicle as a key factor in the decision on vehicle replacement. On the other hand, some other research indicates the potential environmental advantage of extending vehicle lifespan as a way of saving resources, energy and pollution that would otherwise have to be spent on manufacturing new cars [34; 35]. The environmental consequences, including more frequent service and failure, can undermine the advantage of extending the lifespan of older vehicles. A new, more energy efficient and more reliable car can be a better solution. To assess the compromise between extending the car use time and money spent on replacing an old vehicle, it is necessary to have a detailed life cycle inventory (LCI). LCI covers production, use, maintenance and environmental burden linked to vehicle utilization. The negative effect of maintenance is due to emissions, used resources, additional manufacturing processes, distribution of components and service procedures. There are many research studies that provide well-documented life cycle inventories, but they also differ in terms of data details [5]. [PERSON]'s and [PERSON]'s [39] inventory of the VW Golf A4 is probably the most fundamental and thorough LCI of a passenger car. The materials covered by the maintenance schedule include engine oil, coolant, brake fluid, window liquid, tires, filters, battery, wiper blades and spark plugs. The service interval was set at each 15,000 km. The inventory also covers 180 car wash stations and the replacement of a bumper. Data based on the Golf A4 LCI reflect the service actions recorded in Ecoinvent [40], which is the basis of many LCA studies. In most research, maintenance accounts for 2-3% of the total life cycle assessment, while in others it is thought to be negligible. The certified Ford Service Center in Szczecin (Poland) suggests that actually the range of maintenance operations is much wider than in the present public inventories. Realistic maintenance scenarios cover preventive maintenance, planned repairs and difficult-to-predict failures and damage sustained as a result of road accidents. They are also more adjusted to more advanced technology and higher EURO emission standards than those of the Golf A4. All cases of maintenance operations performed on Ford Focus cars (EURO 5) that were regularly serviced in the station were analyzed in terms of technological improvements and environmental efficiency. For example, it was confirmed that diesel cars intensively used in urban environment required oil exchanges every 4-6 thousand kilometers, whereas the producer recommends an interval of 15,000 km. Diesel cars must regularly regenerate diesel particulate filters (DPF) in a special procedure. It requires the driver to maintain an appropriate driving style, best outside the city, preferably on the highway. If the procedure is disrupted in city traffic when cars cover short distances, oil is diluted with the fuel that has not burned. The message telling the driver to change the oil is supposed to protect the engine from failure. It is clear that this kind of real-life scenario multiplies the negative effect of maintenance on the environment. Unplanned repairs and failures had similar adverse effects. This study used LCA to optimize the life cycle of a vehicle to minimize the effect on the environment. The optimization model the study introduced is a compromise between extending the life of an old car and replacing it with a new, more efficient and more reliable model in a given planning horizon. LCA results of environmental profiles, modes of operation, maintenance and utilization were used as input data. Our model is based on a very thorough service documentation of a large vehicle sample compared to other studies. The impact assessment was performed using the ecoinductor EI 99 characterization method for end-point indicators: human health, ecological quality and resource quality.