Clean and zero-emission urban buses: Compliance with EU regulations and fleet transition in Seville

The EU public transport sector is dominated by diesel and natural gas buses, but fleet structures are rapidly changing. EU climate laws drive two strategies: one for bus manufacturers and another for public transport operators (PTO), with different timelines. PTOs must progressively replace fleets with clean and zero-emission buses. This paper develops bus replacement strategies aligned with EU standards, focusing on cost minimization and CO 2 emission reduction. Three propulsion technologies (diesel, compressed natural gas, and electric) and two bus types (regular and articulated) are analyzed. The strategies consider acquisition, operational, and service costs, along with CO 2 emissions. The proposed approach, applied over a 10-year period, uses real-word data from Seville (Spain) PTO to meet EU standards for 2025–2035. Operational data allow precise energy demand estimation, considering propulsion, climatization air compressor, and auxiliaries. CO 2 emissions calculations show that CNG buses emit 24 % more CO 2 per km than diesel buses. Optimization results indicate that a CO 2 minimization strategy reduces emissions by 16.3 %, with only a 6.7 % cost increase compared to the minimal-cost strategy. • Optimizes urban bus fleet transition under EU regulations. • Assesses bus fleet renewal strategies for cost & CO2. • Real-world operational data drive energy & CO2 analysis. • Compares propulsion (Diesel, CNG, Electric) for fleet replacement.