The fossil-fueled public transportation which circulates at inner-city routes is an important focus area for carbon dioxide (CO2) emission researches. As the number of vehicles in the fleets and the cumulative distances covered by these fleets are considerably high, the understanding of effects such as cruising speeds, auxiliary loads, operating planning, and bus stop location choosing becomes more important on CO2 emissions. The European Commission has already set a framework to regulate pollutant emissions and is underway to monitor and regulate CO2 emissions with the use of the Vehicle Energy Calculation Tool (VECTO). VECTO is a vehicle simulation tool developed for the certification and monitoring of fuel consumption and CO2 emissions from heavy-duty vehicles. Trucks are already certified using VECTO since 2019, while work is ongoing for extending the tool and methodology to buses and coaches. In this context, a route in one of the longest bus transport systems − Istanbul Metrobus Rapid Bus Transport System − is modeled in VECTO environment. The model is validated with real driving fuel consumption and CO2 emission results of the buses. The obtained results showed a difference in the range of 1-5%. Further analyses indicated that VECTO could be used for assessing on-road CO2 emissions of conventional buses and assist urban transportation planning and potentially for other regulatory purposes in Turkey as well.