For the transport agencies, it is critical to achieve carbon peaking and carbon neutrality goals in urban area via achieving low-carbon transformation in the energy consumption structure. However, as different agencies are greatly varied in energy structure, emission forms, functions and other aspects, the existing research, often based on macro model measurement, cannot fully reflect the difference and complexity of transportation energy consumption. This study is conducted on the basis of the data of urban transportation energy consumption and takes Nanjing as an example to measure the total amount of CO2 emissions of different urban transportations and discusses whether Nanjing can achieve the traffic carbon peak target by 2030. The results show that, firstly, the low-carbon transformation of urban transportation energy structure plays a decisive role for Nanjing to achieve the target mentioned above; secondly, the reduced intensity of private transportation has less impact on the time to achieve the carbon peak, but has a great impact on lowing the carbon peak value; lastly, the development of motor vehicle emission control technology can effectively reduce the carbon peak value, with less obvious impact on the time to achieve the carbon peak.