The study presented in this paper evaluates cumulative traction energy, well-to-wheel greenhouse-gas emissions, and operating costs for modelled diesel, compressed natural gas (CNG) and super-capacitor electric buses operating on Belgrade's radial public transport line 27. A physics-based longitudinal-dynamics model was calibrated with second-by-second speed, altitude, and passenger-load data collected in field tests, then applied to two complete cycles (Republic Square ↔ Mirijevo 3). Results show that the e-bus required only 47.9 MJ per half-cycle, yielding energy savings of 71% relative to the diesel bus and 82% relative to the CNG bus. Corresponding unit energy demands were 4.74 MJ/km for electric, 16.23 MJ/km for diesel and 25.64 MJ/km for CNG buses. Despite Serbia's coal-dominated electricity mix, well-to-wheel CO₂ emissions from the e-bus remained the lowest at 0.73-0.74 kg/km, while tail-pipe emissions of CO, NOx and PM were eliminated entirely. Traction energy costs followed the same hierarchy 0.17 EUR/km for electric bus, 0.34-0.42 EUR/km for CNG) and 0.51-0.63 EUR/km for diesel buses. Comparative analysis confirmed that road gradient and stop density dominate energy demand. The findings demonstrate that electrification can deliver substantial energy and local-pollution benefits even on hilly, mixed-traffic routes, providing actionable evidence for fleet managers and policy-makers considering propulsion-technology transitions in comparable urban contexts.