###### Abstract  
New propulsion technologies and the development of electromobility increase the environmental efficiency of the transport sector. However, the current structure of car fleets with a large number of old cars with worse environmental parameters undermines the benefits of technological progress in the automotive industry. Older cars may require a more extensive service, involving a thorough overhaul, repair or even replacement of many parts. The result of using additional resources is a deterioration of environmental performance. This study considers various maintenance and repair scenarios and focuses on the use phase using the example of the popular Ford Focus passenger car model. The life cycle optimization model was used for environmental assessment, which determines the optimal duration of the car use phase, accounting for detailed service information and the type and environmental efficiency class of the different fuel versions. This model can be an effective tool for car fleet management and car replacement policy. Detailed life cycle inventories of 40 Ford Focus II diesel and petrol cars that represent all maintenance and repairs are the inputs to the life cycle optimization model. The inventory data were provided by the Ford Service Center in Szczecin (Poland), which regularly serviced the cars with a mileage of up to 200,000 km. Inventory at other stages of the cars' life cycles was modeled using Ecoinvent data. The results show that by considering these vehicle servicing aspects on the basis of more detailed data, impact assessments are better represented compared to other studies. Depending on the replacement policy, the contribution of vehicle maintenance and repair can account for almost half of the cumulative life cycle burdens. life cycle optimization model; life cycle assessment; vehicle maintenance; vehicle repair 2023  
Krzysztof D  
sequences of the best decisions that would guarantee the lowest cumulative cost during vehicle lifetimes. One of the biggest costs for every vehicle fleet is maintenance [4]. Older cars require more extensive service, which involves the thorough overhaul, repair or even replacement of components that prematurely failed. Vehicles with lower repair costs as they get older keep their value better than other cars. A proper strategy of preventive maintenance plays a pivotal role in attempts to maximize vehicle lifespan. More reliable cars can be used for longer to minimize the total operational costs. However, when one of the main components that was supposed to last the vehicle's lifetime fails, the repair cost can exceed the value of the car. Savings from amortization over a long car lifetime cannot make up for the high costs of repairs. In these cases, it is better to retire the vehicle and have it scrapped. It can be concluded that motor vehicle replacement decisions represent a trade-off between the purchase of a new, more efficient and less polluting motor vehicle versus continuing to use and maintain an inefficient, higher-polluting old car. However, environmental assessments based only on drive efficiency can lead to flawed conclusions and non-optimal results. The environmental efficiency of vehicles largely depends on the vehicle's technology. A study conducted by [PERSON] et al. [5] showed how important it is to take into consideration the impact of vehicle production and utilization, particularly when comparing the different vehicle technologies, in particular electric vehicles (EV) and internal combustion engine vehicles (ICEV). Half of the cumulative impact of an EV is linked to production, while for an ICEV most of the impact is linked to driving. In comparative assessments of vehicle environmental efficiency, the differences of drive/fuel technologies are best illustrated in an approach based on life cycle assessment. Apart from production, life cycle also covers the consequences of maintenance and component replacement, recovery and utilization of materials in cars that are scrapped.