Comparison of real driving emissions from Euro VI buses with diesel and compressed natural gas fuels

•Emissions from Euro VI-C Diesel and Compressed Natural Gas (CNG) buses were compared.•Euro VI In Service Conformity (ISC) route requirements were chosen for testing both buses.•Both buses were tested in Madrid, Spain, city with approximately a 6.5 million population.•NOx and particles emitted along the route are mainly affected by the traffic under urban driving.•Both Diesel and CNG buses produced very low emissions compared to Euro VI C limits.