The level of public service significantly influences the quality of life for urban residents. To accurately measure this service level, it is advisable to utilize integrated indicators that consider a comprehensive set of public service parameters. The selection of these parameters should incorporate passenger opinions on their importance, an aspect not fully considered in existing service level assessment approaches. Our research on the significance of these service parameters has enabled the formation of a quantitative evaluation for each. This has facilitated the formalization of an integrated indicator of passenger service level, based on the importance values of each specific indicator. Considered parameters include the duration of the approach to a stop, the waiting time for a bus, the travel duration, and the level of bus occupancy. A developed stochastic model was used to predict the service level of urban routes depending on various transport service parameters. Using this model, we determined how the number of buses on a route impacts the transport service level. The results demonstrated that the number of buses significantly affects service level indicators. It was found that route parameters dictate the optimal number of buses, which ensures the maximum possible level of public service, considering available economic resources. The conducted research has allowed for the mathematical formalization of changes in the optimal number of buses.